From f23e31a673c4bc8b6c9260f640845b16860fc15f Mon Sep 17 00:00:00 2001 From: Jeremie Koenig Date: Tue, 24 May 2011 17:46:58 +0200 Subject: user/jkoenig: reorganize --- user/jkoenig/java/discussion.mdwn | 180 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 180 insertions(+) create mode 100644 user/jkoenig/java/discussion.mdwn (limited to 'user/jkoenig/java') diff --git a/user/jkoenig/java/discussion.mdwn b/user/jkoenig/java/discussion.mdwn new file mode 100644 index 00000000..0131d8d5 --- /dev/null +++ b/user/jkoenig/java/discussion.mdwn @@ -0,0 +1,180 @@ +[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +Some [[tschwinge]] comments regarding your proposal. Which is very good, if I +may say so again! :-) + +Of course, everyone is invited to contribute here! + +I want to give the following methodology a try, instead of only having +email/IRC discussions -- for the latter are again and again showing a tendency +to be dumped and deposited into their respective archives, and be forgotten +there. Of course, email/IRC discussions have their usefulness too, so we're +not going to replace them totally. For example, for conducting discussions +with a bunch of people (who may not even be following these pages here), email +(or, as applicable, the even more interactive IRC) will still be the medium of +choice. (And then, the executive summary should be posted here, or +incorporated into your proposal.) + +Also, if you disagree with this suggested procedure right away, or at some +later point begin to feel that this thing doesn't work out, or simply takes too +much time (I don't think so: writing emails takes time, too), just say so, and +we can reconsider. + +Of course, as this wiki is a passive medium rather than an active one as IRC +and email are, it is fine to send notices like: *I have updated the wiki page, +please have a look*. + +One idea is that your proposal evolves alongside with the ongoing work, and +represents (in more or less detail) what has been done and what will be done. +Also, we can hopefully use parts of it for documentation purposes, or as +recipes for similar work (enabling other programming languages on the Hurd, for +example). + +For this, I suggest the following procedure: as applicable, you can either +address any comments in here (for example, if they're wrong :-), or if they +require further discussion; think: *email discussion*), or you can address them +directly in your propoal and remove the comments from here at the same time +(think: *bug fix*). + +Generally, you can assume that for things I didn't comment on (within some +reasonable timeframe/upon asking me again) that I'm fine with them. Otherwise, +I might say: *I don't like this as is, but I'll need more time to think about +it.* + +There is also a possibility that parts of your proposal will be split off; in +cases where we think they're valuable to follow, but not at this time. (As you +know, your proposal is not really a trivial one, so it may just be too much for +one person's summer.) Such bits could be moved to [[open_issues]] pages, +either new ones or existing ones, as applicable. + + +# POSIX Threads Signal Semantics + + * Great! [[tschwinge]] had a brief look, and should have a deeper one. + + * If [[jkoenig]] thinks it's mature enough: should ask Samuel to test this + (that is, only the refactoring patches for starters?) on the buildds. + + * Then: should ask Roland to review. + + * Documentations bits should probably be moved to [[glibc/signal]]. + + +## libthreads (cthreads) Integration + + * [[tschwinge]] suggests to leave them as-is? + + +## [[libpthread]] integration + + * To be done. + + +# Java + + * [[tschwinge]] has to read about RMI and CORBA. + + +# Joe-E + + * For later. + + +# GCJ + + * [[tschwinge]] has the feeling that Java in GCC (that is, GCJ) is mostly + dead? (True?) + + * Thus perhaps not too much effort should be spent with it. + + If the POSIX threads signal semantics makes it going, then great, otherwise + we should get a feeling what else is missing. + + +# OpenJDK + + * All in all, [[tschwinge]] has the feeling that a working OpenJDK will be + more useful/powerful than GCJ. + + * We need to get a feeling how difficult such an OS port will be. + + * [[jkoenig]] suggests OpenJDK 6 -- should we directly go for version 7 + instead? + + * What are the differences (regarding the OS port) between the two + versions? Or this there something even more recent to be worked upon, + for new OS ports? + + * Perhaps the different versions' OS port specific stuff is not at + all very different, so that both v6 and v7 could be done? + + * They seem to have a rather heavy-weight process for such projects: confer + , + for example. Do we need this, too? + + +# Eclipse + +OK for testing -- but I'd very much hope that it *just works* as soon as we +provide the required Java platform. + + +# Java Bindings + + +## Design Principles + + * Generally ack. + + +### MIG + + * Hacking [[microkernel/mach/MIG]] shouldn't be too difficult. + + * (Unless you want to make MIG's own code (that is, not the generated + code, but MIG itself) look a bit more nice, too.) ;-) + + * There are also alternatives to MIG. If there is interest, the following + could be considered: + + * FLICK ([[!GNU_Savannah_task 5723]]). [[tschwinge]] has no idea yet if + there would be any benefits over MIG, like better modularity (for the + backends)? If we feel like it, we could spend a little bit of time on + this. + + * For [[microkernel/Viengoos]], Neal has written a RPC stub generator + entirely in C Preprocessor macros. While this is obviously not + directly applicable, perhaps we can get some ideas from it. + + * Anything else that would be worth having a look at? (What are other + microkernels using?) + + +### `mach_msg` + + * Seems like the right approach to [[tschwinge]], but hasn't digested all the + pecularities yet. Will definitely need more time. + + +# GSoC Site Discussion + + * Discussion items from + + should be copied here: + + * technical bits (obviously); + + * also the *why do we want Java bindings* reasoning; + + * CLISP findings should also be documented somewhere permanently. + + * We should probaby open up a *languages for Hurd* section on the web + pages ([[!taglink open_issue_documentation]]). -- cgit v1.2.3 From e24c06d392601c1c3a5ead08aea237a4bfa79d03 Mon Sep 17 00:00:00 2001 From: Jeremie Koenig Date: Wed, 15 Jun 2011 16:27:00 +0200 Subject: user/jkoenig: java status report --- user/jkoenig/java.mdwn | 738 ++++++---------------------------------- user/jkoenig/java/proposal.mdwn | 628 ++++++++++++++++++++++++++++++++++ 2 files changed, 740 insertions(+), 626 deletions(-) create mode 100644 user/jkoenig/java/proposal.mdwn (limited to 'user/jkoenig/java') diff --git a/user/jkoenig/java.mdwn b/user/jkoenig/java.mdwn index 4052f455..90f51028 100644 --- a/user/jkoenig/java.mdwn +++ b/user/jkoenig/java.mdwn @@ -1,628 +1,114 @@ +[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +# Improve Java on Hurd (GSoC 2011) + + +## Description + +The project consists in improving Java support on Hurd. +This includes porting OpenJDK, +creating low-level Java bindings for Mach and Hurd, +as well as creating Java libraries to help with translator development. + +For details, see my original [[proposal]]. + + +## Current status + + +### Apt repository + +Modified Debian packages are available in this repository: + + deb http://jk.fr.eu.org/debian experimental/ + deb-src http://jk.fr.eu.org/debian experimental/ + + +### Glibc signal code improvements + +I have submitted +[preliminary patches](http://lists.gnu.org/archive/html/bug-hurd/2011-05/msg00182.html) +for global signal dispositions, +which I'm currently testing. +I have since fixed a few thinks and implemented `SA_SIGINFO` +(which is required by OpenJDK.) +My latest code is available on +[github](http://github.com/jeremie-koenig/glibc/commits/master-beware-rebase), +and modified Debian packages +are available in my apt repository. + +One question is how the new symbols introduced by my patches +should be handled. +Weak symbols turned out to be impractical, +so I'm currently considering using a Debian-specific +symbol version in the interim period (`GLIBC_2.13_DEBIAN_7` so far). +The ultimate symbol version to be used will depend on +the time at which the patches get integrated upstream, +at which point we will alias the interim version +to the new one in debian packages. + +I have modified libc0.3 to include a `deb-symbols(5)` file +so that we get an accurate libc dependency in `hurd` and other packages +when the symbols in question are pulled in. + +Another issue which came up with OpenJDK is the expansion +by the dynamic linker of `$ORIGIN` in the `RPATH` header, +see below. + +#### Plans + +I will submit revised series for review later this week, +as well as matching Debian patches. +I expect only the last patch (implement global dispositions) will change, +and new ones will be added on top of it. + + +### Port OpenJDK + +As suggested by [[tschwinge]], I have targeted OpenJDK 7 at first. +I don't expect it will be too hard to backport my patches to OpenJDK 6. +I have succeeded in building a working JIT-less ("zero") version, +although the dynamic linker issue must be worked around. +Porting Hotspot (the original just-in-time compiler of OpenJDK) +should not be too hard. +If that fails we can fall back on Shark +(a portable alternative JIT which uses LLVM). + +The dynamic linker issue is as follows. +An executable-specific search path can be provided in the ELF RPATH header. +RPATH directories can include the special string `$ORIGIN`, +which is to be expanded to the directory the executable was loaded from. +OpenJDK's `java` command uses this feature to locate +the right `libjli.so` at runtime. +However, +on Hurd this information is not available to the dynamic linker +and as a consequence RPATH components which include `$ORIGIN` +are silently discarded. + +This can be worked around by defining +the `LD_ORIGIN_PATH` environment variable. +(which have I used to build and test OpenJDK so far.) + +#### Plans + +I intend to fix the RPATH issue +by building on [[pochu]]'s `file_exec_file_name()` patches. + +I have succeeded in building a Hotspot-enabled `libjvm.so`, +although the current toolchain issues +have so far prevented me from testing it. + + +### Java bindings for Mach + +(just started.) -# Java for Hurd (and vice versa) - -Contact information: - - * Full name: Jérémie Koenig - * Email: jk@jk.fr.eu.org - * IRC: jkoenig on Freenode and OFTC - -## Introductions - -I am a first year M.Sc. student -in Computer Science at University of Strasbourg (France). -My interests include capability-based security, -programming languages and formal methods -(in particular, object-capability languages and proof-carrying code). - -### Proposal summary - -This project would consist in improving Java support on Hurd. -The first part would consist in -fixing bugs and porting Java-related packages. -The second part would consist in -creating low-level Java bindings for the Hurd interfaces, -as well as libraries to make translator development easier. - -### Previous involvement - -I started contributing to Hurd last summer, -during which I participated to Google Summer of Code -as a student for the Debian project. -I worked on porting Debian-Installer to Hurd. -This project was mostly a success, -although we still have to use a special mirror for installation -with a few modified packages -and tweaked priorities -to work around some uninstallable packages -with Priority: standard. - -Shortly afterwards, -I rewrote the procfs translator -to fix some issues with memory leaks, -make it more reliable, -and improve compatibility with Linux-based tools -such as `procps` or `htop`. - -Although I have not had as much time -as I would have liked to dedicate to the Hurd -since that time, -I have continued to maintain the mirror in question, -and I have started to work -on implementing POSIX threads signal semantics in glibc. - -### Project-related skills and interests - -I have used Java mostly for university assignments. -This includes non-trivial projects -using threads and distributed programming frameworks -such as Java RMI or CORBA. -I have also used it to experiment with -Google App Engine -(web applications) -and Google Web Toolkit -(a compiler from Java to Javascript which helps with AJAX code), -and I have some limited experience with JNI -(the Java Native Interface, to link Java with C code). - -My knowledge of the Hurd and Debian GNU/Hurd is reasonable, -as the Debian-Installer and procfs projects -gave me the opportunity to fiddle with many parts of the system. - -Initially, -I started working on this project because I wanted to use -[Joe-E](http://code.google.com/p/joe-e/) -(a subset of Java) -to investigate the potential -[[applications of object-capability languages|objcap]] -in a Hurd context. -I also believe that improving Java support on Hurd -would be an important milestone. - -### Organisational matters - -I am subscribed to bug-hurd@g.o and -I do have a permanent internet connexion. - -I would be able to attend the regular IRC meetings, -and otherwise communicate with my mentor -through any means they would prefer -(though I expect email and IRC would be the most practical). -Since I'm already familiar with the Hurd, -I don't expect I would require too much time from them. - -My exams end on May 20 so I would be able to start coding -right at the beginning of the GSoC period. -Next year's term would probably begin around September 15, -so that would not be an issue either. -I expect I would work around 40 hours per week, -and my waking hours would be flexible. - -I don't have any other plans for the summer -and would not make any if my project were to be accepted. - -Full disclosure: -I also submitted a proposal to the Jikes RVM project -(which is a research-oriented Java Virtual Machine, -itself written in Java) -for implementing a new garbage collector into the MMTk subsystem. - -## Improve Java support - -### Justification - -Java is a popular language and platform used by many desktop and web -applications (mostly on the server side). As a consequence, competitive Java -support is important for any general-purpose operating system. -Better Java support would also be a prerequisite -for the second part of my proposal. - -### Current situation - -Java is currently supported on Hurd with the GNU Java suite: - - * [GCJ](http://gcc.gnu.org/java/), - the GNU Compiler for Java, is part of GCC and can compile Java - source code to Java bytecode, and both source code and bytecode to - native code; - * libgcj is the implementation of the Java runtime which GCJ uses. - It is based on [GNU Classpath](http://www.gnu.org/software/classpath/). - It includes a bytecode interpreter which enables - Java applications compiled to native code to dynamically load and execute - Java bytecode from class files. - * The gij command is a wrapper around the above-mentioned virtual machine - functionality of libgcj and can be used as a replacement for the java - command. - -However, GCJ does not work flawlessly on Hurd.r -For instance, some parts of libgcj relies on -the POSIX threads signal semantics, which are not yet implemented. -In particular, this makes ant hang waiting for child processes, -which makes some packages fail to build on Hurd -(“ant” is the “make” of the Java world). - -### Tasks - - * **Finish implementing POSIX thread semantics** in glibc (high priority). - According to POSIX, signal dispositions should be global to a process, - while signal blocking masks should be thread-specific. Signals sent to the - process as a whole are to be delivered to any thread which does not block - them. By contrast, Hurd has per-thread signal dispositions and signals - sent to a process are delivered to the main thread only. I have been - working on refactoring the glibc signal code and implementing the POSIX - semantics as a per-thread option. However, due to lack of time I have not - yet been able to test and debug my code properly. Finishing this work - would be my first task. - * **Fix further problems with GCJ on Hurd** (high priority). While I’m not - aware of any other problems with GCJ at the moment, I suspect some might - turn up as I progress with the other tasks. Fixing these problems would - also be a high-priority task. - * **Port OpenJDK 6** (medium priority). While GCJ is fine, it is not yet - 100% complete. It is also slower than OpenJDK on architectures where a - just-in-time compiler is available. Porting OpenJDK would therefore - improve Java support on Hurd in scope and quality. Besides, it would also - be a good way to test GCJ, which is used for bootstrapping by the Debian - OpenJDK packages. Also note that OpenJDK 6 is now the default Java - Runtime Environment on all released Linux-based Debian architectures; - bringing Hurd in line with this would probably be a good thing. - * **Port Eclipse and other Java applications** (low priority). Eclipse is a - popular, state-of-the-art IDE and tool suite used for Java and other - languages. It is a dependency of the Joe-E verifier (see part 3 of this - proposal). Porting Eclipse would be a good opportunity to test GCJ and - OpenJDK. - -### Deliverables - - * The glibc pthreads patch and any other fixes on the Hurd side - would be submitted upstream - * Patches against Debian source packages - required to make them build on Hurd would be submitted - to the [Debian bug tracking system](http://bugs.debian.org/). - - -## Create Java bindings for the Hurd interfaces - -### Justification - -Java is used for many applications and often taught to -introduce object-oriented programming. The fact that Java is a -garbage-collected language makes it easier to use, especially for the less -experienced programmers. Besides, its object-oriented nature is a -natural fit for the capability-based design of Hurd. -The JVM is also used as a target for many other languages, -all of which would benefit from the access provided by these bindings. - -Advantages over other garbage-collected, object-oriented languages include -performance, type safety and the possibility to compile a Java translator to -native code and -[link it statically](http://gcc.gnu.org/wiki/Statically_linking_libgcj) -using GCJ, should anyone want to use a -translator written in Java for booting. -Note that Java is -[being](http://www.linuxjournal.com/article/8757) -[used](http://oss.readytalk.com/avian/) -in this manner for embedded development. -Since GCJ can take bytecode as its input, -this expect this possibility would apply to any JVM-based language. - -Java bindings would lower the bar for newcomers -to begin experimenting with what makes Hurd unique -without being faced right away with the complexity of -low-level systems programming. - -### Tasks summary - - * Implement Java bindings for Mach - * Implement a libports-like library for Java - * Modify MIG to output Java code - * Implement libfoofs-like Java libraries - -### Design principles - -The principles I would use to guide the design -of these Java bindings would be the following ones: - - * The system should be hooked into at a low level, - to ensure that Java is a "first class citizen" - as far as the access to the Hurd's interfaces is concerned. - * At the same time, the memory safety of Java should be maintained - and extended to Mach primitives such as port names and - out-of-line memory regions. - * Higher-level interfaces should be provided as well - in order to make translator development - as easy as possible. - * A minimum amount of JNI code (ie. C code) should be used. - Most of the system should be built using Java itself - on top of a few low-level primitives. - * Hurd objects would map to Java objects. - * Using the same interfaces, - objects corresponding to local ports would be accessed directly, - and remote objects would be accessed over IPC. - -One approach used previously to interface programming languages with the Hurd -has been to create bindings for helper libraries such as libtrivfs. Instead, -for Java I would like to take a lower-level approach by providing access to -Mach primitives and extending MIG to generate Java code from the interface -description files. - -This approach would be initially more involved, and would introduces several -issues related to overcoming the "impedance mismatch" between Java and Mach. -However, once an initial implementation is done it would be easier to maintain -in the long run and we would be able to provide Java bindings for a large -percentage of the Hurd’s interfaces. - -### Bindings for Mach system calls - -In this low-level approach, my intention is to enable Java code to use Mach -system calls (in particular, mach_msg) more or less directly. This would -ensure full access to the system from Java code, but it raises a number of -issues: - - * the Java code must be able to manipulate Mach-level entities, such as port - rights or page-aligned buffers mapped outside of the garbage-collected - heap (for out-of-line transfers); - * putting together IPC messages requires control of the low-level - representation of data. - -In order to address these concerns, classes would be encapsulating these -low-level entities so that they can be referenced through normal, safe objects -from standard Java code. Bindings for Mach system calls can then be provided -in terms of these classes. Their implementation would use C code through the -Java Native Interface (JNI). - -More specifically, this functionality would be provided by the `org.gnu.mach` -package, which would contain at least the following classes: - - * `MachPort` would encapsulate a `mach_port_t`. (Some of) its constructors - would act as an interface for the `mach_port_allocate()` system call. - `MachPort` objects would also be instantiated from other parts of the JNI - C code to represent port rights received through IPC. The `deallocate()` - method would call `mach_port_deallocate()` and replace the encapsulated - port name with `MACH_PORT_DEAD`. We would recommend that users call it - when a port is no longer used, but the finalizer would also deallocate the - port when the `MachPort` object is garbage collected. - * `Buffer` would represent a page-aligned buffer allocated outside of the - Java heap, to be transferred (or having been received) as out-of-line - memory. The JNI code would would provide methods to read and write data at - an arbitrary offset (but within bounds) and would use `vm_allocate()` and - `vm_deallocate()` in the same spirit as for `MachPort` objects. - * `Message` would allow Java code to put together Mach messages. The - constructor would allocate a `byte[]` member array of a given size. - Additional methods would be provided to fill in or query the information - in the message header and additional data items, including `MachPort` and - `Buffer` objects which would be translated to the corresponding port names - and out-of-line pointers. - A global map from port names to the corresponding `MachPort` object - would probably be needed to ensure that there is a one-to-one - correspondence. - * `Syscall` would provide static JNI methods for performing system calls not - covered by the above classes, such as `mach_msg()` or - `mach_thread_self()`. These methods would accept or return `MachPort`, - `Buffer` and `Message` objects when appropriate. The associated C code - would access the contents of such objects directly in order to perform the - required unsafe operations, such as constructing `MachPort` and `Buffer` - objects directly from port names and C pointers. - -Note that careful consideration should be given to the interfaces of these -classes to avoid “safety leaks” which would compromise the safety guarantees -provided by Java. Potential problematic scenarios include the following -examples: - - * It must not be possible to write an integer at some position in a - `Message` object, and to read it back as a `MachPort` or `Buffer` object, - since this would allow unsafe access to arbitrary memory addresses and - mach port names. - * Providing the `mach_task_self()` system call would also provide access to - arbitrary addresses and ports by using the `vm_*` family of RPC operations - with the returned `MachPort` object. This means that the relevant task - operations should be provided by the `Syscall` class instead. - -Finally, access should be provided to the initial ports and file descriptors -in `_hurd_ports` and provided by the `getdport()` function, -for instance through static methods such as -`getCRDir()`, `getCWDir()`, `getProc()`, ... in a dedicated class such as -`org.gnu.hurd.InitPorts`. - -A realistic example of code based on such interfaces would be: - - import org.gnu.mach.MsgType; - import org.gnu.mach.MachPort; - import org.gnu.mach.Buffer; - import org.gnu.mach.Message; - import org.gnu.mach.Syscall; - import org.gnu.hurd.InitPorts; - - public class Hello - { - public static main(String argv[]) - /* Parent class for all Mach-related exceptions */ - throws org.gnu.mach.MachException - { - /* Allocate a reply port */ - MachPort reply = new MachPort(); - - /* Allocate an out-of-line buffer */ - Buffer data = new Buffer(MsgType.CHAR, 13); - data.writeString(0, "Hello, World!"); - - /* Craft an io_write message */ - Message msg = new Message(1024); - msg.setRemotePort(InitPorts.getdport(1)); - msg.setLocalPort(reply, Message.Type.MAKE_SEND_ONCE); - msg.setId(21000); - msg.addBuffer(data); - - /* Make the call, MACH_MSG_SEND | MACH_MSG_RECEIVE */ - Syscall.machMsg(msg, true, true, reply); - - /* Extract the returned value */ - msg.assertId(21100); - int retCode = msg.readInt(0); - int amount = msg.readInt(1); - } - } - -Should this paradigm prove insufficient, -more ideas could be borrowed from the -[`org.vmmagic`](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.151.5253&rep=rep1&type=pdf) -package used by [Jikes RVM](http://jikesrvm.org/), -a research Java virtual machine itself written in Java. - -### Generating Java stubs with MIG - -Once the basic machinery is in place to interface with Mach, Java programs -have more or less equal access to the system functionality without resorting -to more JNI code. However, as illustrated above, this access is far from -convenient. - -As a solution I would modify MIG to add the option to output Java code. MIG -would emit a Java interface, a client class able to implement the interface -given a Mach port send right, an a server class which would be able to handle -incoming messages. The class diagram below, although it is by no means -complete or exempt of any problem, illustrates the general idea: - -[[gsoc2011_classes.png]] - -This structure is somewhat reminiscent of -[Java RMI](http://en.wikipedia.org/wiki/Java_remote_method_invocation) -or similar systems, -which aim to provide more or less transparent access to remote objects. -The exact way the Java code would be generated still needs to be determined, -but basically: - - * An interface, corresponding to the header files generated by MIG, would - enumerate the operations listed in a given .defs files. Method names would - be transformed to adhere to Java conventions (for instance, - `some_random_identifier` would become `someRandomIdentifier`). - * A user class, corresponding to the `*User.c` files, - would implement this interface by doing RPC over a given MachPort object. - * A server class, corresponding to `*Server.c`, would be able to handle - incoming messages using a user-provided implementation of the interface. - (Possibly, a skeleton class providing methods which would raise - `NotImplementedException`s would be provided as well. - Users would derive from this class and override the relevant methods. - This would allow them not to implement some operations, - and would avoid pre-existing code from breaking when new operations are - introduced.) - -In order to help with the implementation of servers, some kind of library -would be needed to associate Mach receive rights with server objects and to -handle incoming messages on dedicated threads, in the spirit of libports. -This would probably require support for port sets at the level of the Mach -primitives described in the previous section. - -When possible, operations involving the transmission of send rights -of some kind would be expressed in terms of the MIG-generated interfaces -instead of `MachPort` objects. -Upon reception of a send right, -a `FooUser` object would be created -and associated with the corresponding `MachPort` object. -If the received send right corresponds to a local port -to which a server object has been associated, -this object would be used instead. -This way, -subsequent operations on the received send right -would be handled as direct method calls -instead of going through RPC mechanisms. - -Some issues will still need to be solved regarding how MIG will convert -interface description files to Java interfaces. For instance: - - * `.defs` files are not explicitly associated with a type. For instance in - the example above, MIG would have to somehow infer that io_t corresponds - to `this` in the `Io` interface. - * More generally, a correspondence between MIG and Java types would have - to be determined. Ideally this would be automated and not hardcoded - too much. - * Initially, reply port parameters would be ignored. However they may be - needed for some applications. - -So the details would need to be flushed out during the community bonding -period and as the implementation progresses. However I’m confident that a -satisfactory solution can be designed. - -Using these new features, the example above could be rewritten as: - - import org.gnu.hurd.InitPorts; - import org.gnu.hurd.Io; - import org.gnu.hurd.IoUser; - - class Hello { - static void main(String argv[]) throws ... - { - Io stdout = new IoUser(InitPorts.getdport(1)); - String hello = “Hello, World!\n”; - - int amount = stdout.write(hello.getBytes(), -1); - - /* (A retCode corresponding to an error - would be signalled as an exception.) */ - } - } - -An example of server implementation would be: - - import org.gnu.hurd.Io; - import java.util.Arrays; - - class HelloIo implements Io { - final byte[] contents = “Hello, World!\n”.getBytes(); - - int write(byte[] data, int offset) { - return SOME_ERROR_CODE; - } - - byte[] read(int offset, int amount) { - return Arrays.copyOfRange(contents, offset, - offset + amount - 1); - } - - /* ... */ - } - -A new server object could then be created with `new IoServer(new HelloIo())`, -and associated with some receive right at the level of the ports management -library. - -### Base classes for common types of translators - -Once MIG can target Java code, and a libports equivalent is available, -creating new translators in Java would be greatly facilitated. However, -we would probably want to introduce basic implementations of file system -translators in the spirit of libtrivfs or libnetfs. They could take the form -of base classes implementing the relevant MIG-generated interfaces which -would then be derived by users, -or could define a simpler interface -which would then be used by adapter classes -to implement the required ones. - -I would draw inspiration from libtrivfs and libnetfs -to design and implement similar solutions for Java. - -### Deliverables - - * A hurd-java package would contain the Java code developed - in the context of this project. - * The Java code would be documented using javadoc - and a tutorial for writing translators would be written as well. - * Modifications to MIG would be submitted upstream, - or a patched MIG package would be made available. - -The Java libraries resulting from this work, -including any MIG support classes -as well as the class files built from the MIG-generated code -for the Mach and Hurd interface definition files, -would be provided as single `hurd-java` package for -Debian GNU/Hurd. -This package would be separate from both Hurd and Mach, -so as not to impose unreasonable build dependencies on them. - -I expect I would be able to act as its maintainer in the foreseeable future, -either as an individual or as a part of the Hurd team. -Hopefully, -my code would be claimed by the Hurd project as their own, -and consequently the modifications to MIG -(which would at least conceptually depend on the Mach Java package) -could be integrated upstream. - -Since by design, -the Java code would use only a small number of stable interfaces, -it would not be subject to excessive amounts of bitrot. -Consequently, -maintenance would primarily consist in -fixing bugs as they are reported, -and adding new features as they are requested. -A large number of such requests -would mean the package is useful, -so I expect that the overall amount of work -would be correlated with the willingness of more people -to help with maintenance -should I become overwhelmed or get hit by a bus. - - -## Timeline - -The dates listed are deadlines for the associated tasks. - - * *Community bonding period.* - Discuss, refine and complete the design of the Java bindings - (in particular the MIG and "libports" parts) - * *May 23.* - Coding starts. - * *May 30.* - Finish implementing pthread signal semantics. - * *June 5.* - Port OpenJDK - * *June 12.* - Fix the remaining problems with GCJ and/or OpenJDK, - possibly port Eclipse or other big Java packages. - * *June 19.* - Create the bindings for Mach. - * *June 26.* - Work on some kind of basic Java libports - to handle receive rights. - * *July 3.* - Test, write some documentation and examples. - * *July 17 (two weeks).* - Add the Java target to MIG. - * *July 24.* - Test, write some documentation and examples. - * *August 7 (two weeks).* - Implement a modular libfoofs to help with translator development. - Try to write a basic but non-trivial translator - to evaluate the performance and ease of use of the result, - rectify any rough edges this would uncover. - * *August 22. (last two weeks)* - Polish the code and packaging, - finish writing the documentation. - - -## Conclusion - -This project is arguably ambitious. -However, I have been thinking about it for some time now -and I'm confident I would be able to accomplish most of it. - -In the event multiple language bindings projects -would be accepted, -some work could probably be done in common. -In particular, -[ArneBab](http://www.bddebian.com/~hurd-web/community/weblogs/ArneBab/2011-04-06-application-pyhurd/) -seems to favor a low-level approach for his Python bindings as I do for Java, -and I would be happy to discuss API design and coordinate MIG changes with him. -I would also have an extra month after the end of the GSoC period -before I go back to school, -which I would be able to use to finish the project -if there is some remaining work. -(Last year's rewrite of procfs was done during this period.) - -As for the project's benefits, -I believe that good support for Java -is a must-have for the Hurd. -Java bindings would also further the Hurd's agenda -of user freedom by extending this freedom to more people: -I expect the set of developers -who would be able to write Java code against a well-written libfoofs -is much larger than -those who master the intricacies of low-level systems C programming. -From a more strategic point of view, -this would also help recruit new contributors -by providing an easier path to learning the inner workings of the Hurd. - -Further developments -which would build on the results of this project -include my planned [[experiment with Joe-E|objcap]] -(which I would possibly take on as a university project next year). -Another possibility would be to reimplement some parts -of the Java standard library -directly in terms of the Hurd interfaces -instead of using the POSIX ones through glibc. -This would possibly improve the performance -of some Java applications (though probably not by much), -and would otherwise be a good project -for someone trying to get acquainted with Hurd. - -Overall, I believe this project would be fun, interesting and useful. -I hope that you will share this sentiment -and give me the opportunity to spend another summer working on Hurd. diff --git a/user/jkoenig/java/proposal.mdwn b/user/jkoenig/java/proposal.mdwn new file mode 100644 index 00000000..4052f455 --- /dev/null +++ b/user/jkoenig/java/proposal.mdwn @@ -0,0 +1,628 @@ + +# Java for Hurd (and vice versa) + +Contact information: + + * Full name: Jérémie Koenig + * Email: jk@jk.fr.eu.org + * IRC: jkoenig on Freenode and OFTC + +## Introductions + +I am a first year M.Sc. student +in Computer Science at University of Strasbourg (France). +My interests include capability-based security, +programming languages and formal methods +(in particular, object-capability languages and proof-carrying code). + +### Proposal summary + +This project would consist in improving Java support on Hurd. +The first part would consist in +fixing bugs and porting Java-related packages. +The second part would consist in +creating low-level Java bindings for the Hurd interfaces, +as well as libraries to make translator development easier. + +### Previous involvement + +I started contributing to Hurd last summer, +during which I participated to Google Summer of Code +as a student for the Debian project. +I worked on porting Debian-Installer to Hurd. +This project was mostly a success, +although we still have to use a special mirror for installation +with a few modified packages +and tweaked priorities +to work around some uninstallable packages +with Priority: standard. + +Shortly afterwards, +I rewrote the procfs translator +to fix some issues with memory leaks, +make it more reliable, +and improve compatibility with Linux-based tools +such as `procps` or `htop`. + +Although I have not had as much time +as I would have liked to dedicate to the Hurd +since that time, +I have continued to maintain the mirror in question, +and I have started to work +on implementing POSIX threads signal semantics in glibc. + +### Project-related skills and interests + +I have used Java mostly for university assignments. +This includes non-trivial projects +using threads and distributed programming frameworks +such as Java RMI or CORBA. +I have also used it to experiment with +Google App Engine +(web applications) +and Google Web Toolkit +(a compiler from Java to Javascript which helps with AJAX code), +and I have some limited experience with JNI +(the Java Native Interface, to link Java with C code). + +My knowledge of the Hurd and Debian GNU/Hurd is reasonable, +as the Debian-Installer and procfs projects +gave me the opportunity to fiddle with many parts of the system. + +Initially, +I started working on this project because I wanted to use +[Joe-E](http://code.google.com/p/joe-e/) +(a subset of Java) +to investigate the potential +[[applications of object-capability languages|objcap]] +in a Hurd context. +I also believe that improving Java support on Hurd +would be an important milestone. + +### Organisational matters + +I am subscribed to bug-hurd@g.o and +I do have a permanent internet connexion. + +I would be able to attend the regular IRC meetings, +and otherwise communicate with my mentor +through any means they would prefer +(though I expect email and IRC would be the most practical). +Since I'm already familiar with the Hurd, +I don't expect I would require too much time from them. + +My exams end on May 20 so I would be able to start coding +right at the beginning of the GSoC period. +Next year's term would probably begin around September 15, +so that would not be an issue either. +I expect I would work around 40 hours per week, +and my waking hours would be flexible. + +I don't have any other plans for the summer +and would not make any if my project were to be accepted. + +Full disclosure: +I also submitted a proposal to the Jikes RVM project +(which is a research-oriented Java Virtual Machine, +itself written in Java) +for implementing a new garbage collector into the MMTk subsystem. + +## Improve Java support + +### Justification + +Java is a popular language and platform used by many desktop and web +applications (mostly on the server side). As a consequence, competitive Java +support is important for any general-purpose operating system. +Better Java support would also be a prerequisite +for the second part of my proposal. + +### Current situation + +Java is currently supported on Hurd with the GNU Java suite: + + * [GCJ](http://gcc.gnu.org/java/), + the GNU Compiler for Java, is part of GCC and can compile Java + source code to Java bytecode, and both source code and bytecode to + native code; + * libgcj is the implementation of the Java runtime which GCJ uses. + It is based on [GNU Classpath](http://www.gnu.org/software/classpath/). + It includes a bytecode interpreter which enables + Java applications compiled to native code to dynamically load and execute + Java bytecode from class files. + * The gij command is a wrapper around the above-mentioned virtual machine + functionality of libgcj and can be used as a replacement for the java + command. + +However, GCJ does not work flawlessly on Hurd.r +For instance, some parts of libgcj relies on +the POSIX threads signal semantics, which are not yet implemented. +In particular, this makes ant hang waiting for child processes, +which makes some packages fail to build on Hurd +(“ant” is the “make” of the Java world). + +### Tasks + + * **Finish implementing POSIX thread semantics** in glibc (high priority). + According to POSIX, signal dispositions should be global to a process, + while signal blocking masks should be thread-specific. Signals sent to the + process as a whole are to be delivered to any thread which does not block + them. By contrast, Hurd has per-thread signal dispositions and signals + sent to a process are delivered to the main thread only. I have been + working on refactoring the glibc signal code and implementing the POSIX + semantics as a per-thread option. However, due to lack of time I have not + yet been able to test and debug my code properly. Finishing this work + would be my first task. + * **Fix further problems with GCJ on Hurd** (high priority). While I’m not + aware of any other problems with GCJ at the moment, I suspect some might + turn up as I progress with the other tasks. Fixing these problems would + also be a high-priority task. + * **Port OpenJDK 6** (medium priority). While GCJ is fine, it is not yet + 100% complete. It is also slower than OpenJDK on architectures where a + just-in-time compiler is available. Porting OpenJDK would therefore + improve Java support on Hurd in scope and quality. Besides, it would also + be a good way to test GCJ, which is used for bootstrapping by the Debian + OpenJDK packages. Also note that OpenJDK 6 is now the default Java + Runtime Environment on all released Linux-based Debian architectures; + bringing Hurd in line with this would probably be a good thing. + * **Port Eclipse and other Java applications** (low priority). Eclipse is a + popular, state-of-the-art IDE and tool suite used for Java and other + languages. It is a dependency of the Joe-E verifier (see part 3 of this + proposal). Porting Eclipse would be a good opportunity to test GCJ and + OpenJDK. + +### Deliverables + + * The glibc pthreads patch and any other fixes on the Hurd side + would be submitted upstream + * Patches against Debian source packages + required to make them build on Hurd would be submitted + to the [Debian bug tracking system](http://bugs.debian.org/). + + +## Create Java bindings for the Hurd interfaces + +### Justification + +Java is used for many applications and often taught to +introduce object-oriented programming. The fact that Java is a +garbage-collected language makes it easier to use, especially for the less +experienced programmers. Besides, its object-oriented nature is a +natural fit for the capability-based design of Hurd. +The JVM is also used as a target for many other languages, +all of which would benefit from the access provided by these bindings. + +Advantages over other garbage-collected, object-oriented languages include +performance, type safety and the possibility to compile a Java translator to +native code and +[link it statically](http://gcc.gnu.org/wiki/Statically_linking_libgcj) +using GCJ, should anyone want to use a +translator written in Java for booting. +Note that Java is +[being](http://www.linuxjournal.com/article/8757) +[used](http://oss.readytalk.com/avian/) +in this manner for embedded development. +Since GCJ can take bytecode as its input, +this expect this possibility would apply to any JVM-based language. + +Java bindings would lower the bar for newcomers +to begin experimenting with what makes Hurd unique +without being faced right away with the complexity of +low-level systems programming. + +### Tasks summary + + * Implement Java bindings for Mach + * Implement a libports-like library for Java + * Modify MIG to output Java code + * Implement libfoofs-like Java libraries + +### Design principles + +The principles I would use to guide the design +of these Java bindings would be the following ones: + + * The system should be hooked into at a low level, + to ensure that Java is a "first class citizen" + as far as the access to the Hurd's interfaces is concerned. + * At the same time, the memory safety of Java should be maintained + and extended to Mach primitives such as port names and + out-of-line memory regions. + * Higher-level interfaces should be provided as well + in order to make translator development + as easy as possible. + * A minimum amount of JNI code (ie. C code) should be used. + Most of the system should be built using Java itself + on top of a few low-level primitives. + * Hurd objects would map to Java objects. + * Using the same interfaces, + objects corresponding to local ports would be accessed directly, + and remote objects would be accessed over IPC. + +One approach used previously to interface programming languages with the Hurd +has been to create bindings for helper libraries such as libtrivfs. Instead, +for Java I would like to take a lower-level approach by providing access to +Mach primitives and extending MIG to generate Java code from the interface +description files. + +This approach would be initially more involved, and would introduces several +issues related to overcoming the "impedance mismatch" between Java and Mach. +However, once an initial implementation is done it would be easier to maintain +in the long run and we would be able to provide Java bindings for a large +percentage of the Hurd’s interfaces. + +### Bindings for Mach system calls + +In this low-level approach, my intention is to enable Java code to use Mach +system calls (in particular, mach_msg) more or less directly. This would +ensure full access to the system from Java code, but it raises a number of +issues: + + * the Java code must be able to manipulate Mach-level entities, such as port + rights or page-aligned buffers mapped outside of the garbage-collected + heap (for out-of-line transfers); + * putting together IPC messages requires control of the low-level + representation of data. + +In order to address these concerns, classes would be encapsulating these +low-level entities so that they can be referenced through normal, safe objects +from standard Java code. Bindings for Mach system calls can then be provided +in terms of these classes. Their implementation would use C code through the +Java Native Interface (JNI). + +More specifically, this functionality would be provided by the `org.gnu.mach` +package, which would contain at least the following classes: + + * `MachPort` would encapsulate a `mach_port_t`. (Some of) its constructors + would act as an interface for the `mach_port_allocate()` system call. + `MachPort` objects would also be instantiated from other parts of the JNI + C code to represent port rights received through IPC. The `deallocate()` + method would call `mach_port_deallocate()` and replace the encapsulated + port name with `MACH_PORT_DEAD`. We would recommend that users call it + when a port is no longer used, but the finalizer would also deallocate the + port when the `MachPort` object is garbage collected. + * `Buffer` would represent a page-aligned buffer allocated outside of the + Java heap, to be transferred (or having been received) as out-of-line + memory. The JNI code would would provide methods to read and write data at + an arbitrary offset (but within bounds) and would use `vm_allocate()` and + `vm_deallocate()` in the same spirit as for `MachPort` objects. + * `Message` would allow Java code to put together Mach messages. The + constructor would allocate a `byte[]` member array of a given size. + Additional methods would be provided to fill in or query the information + in the message header and additional data items, including `MachPort` and + `Buffer` objects which would be translated to the corresponding port names + and out-of-line pointers. + A global map from port names to the corresponding `MachPort` object + would probably be needed to ensure that there is a one-to-one + correspondence. + * `Syscall` would provide static JNI methods for performing system calls not + covered by the above classes, such as `mach_msg()` or + `mach_thread_self()`. These methods would accept or return `MachPort`, + `Buffer` and `Message` objects when appropriate. The associated C code + would access the contents of such objects directly in order to perform the + required unsafe operations, such as constructing `MachPort` and `Buffer` + objects directly from port names and C pointers. + +Note that careful consideration should be given to the interfaces of these +classes to avoid “safety leaks” which would compromise the safety guarantees +provided by Java. Potential problematic scenarios include the following +examples: + + * It must not be possible to write an integer at some position in a + `Message` object, and to read it back as a `MachPort` or `Buffer` object, + since this would allow unsafe access to arbitrary memory addresses and + mach port names. + * Providing the `mach_task_self()` system call would also provide access to + arbitrary addresses and ports by using the `vm_*` family of RPC operations + with the returned `MachPort` object. This means that the relevant task + operations should be provided by the `Syscall` class instead. + +Finally, access should be provided to the initial ports and file descriptors +in `_hurd_ports` and provided by the `getdport()` function, +for instance through static methods such as +`getCRDir()`, `getCWDir()`, `getProc()`, ... in a dedicated class such as +`org.gnu.hurd.InitPorts`. + +A realistic example of code based on such interfaces would be: + + import org.gnu.mach.MsgType; + import org.gnu.mach.MachPort; + import org.gnu.mach.Buffer; + import org.gnu.mach.Message; + import org.gnu.mach.Syscall; + import org.gnu.hurd.InitPorts; + + public class Hello + { + public static main(String argv[]) + /* Parent class for all Mach-related exceptions */ + throws org.gnu.mach.MachException + { + /* Allocate a reply port */ + MachPort reply = new MachPort(); + + /* Allocate an out-of-line buffer */ + Buffer data = new Buffer(MsgType.CHAR, 13); + data.writeString(0, "Hello, World!"); + + /* Craft an io_write message */ + Message msg = new Message(1024); + msg.setRemotePort(InitPorts.getdport(1)); + msg.setLocalPort(reply, Message.Type.MAKE_SEND_ONCE); + msg.setId(21000); + msg.addBuffer(data); + + /* Make the call, MACH_MSG_SEND | MACH_MSG_RECEIVE */ + Syscall.machMsg(msg, true, true, reply); + + /* Extract the returned value */ + msg.assertId(21100); + int retCode = msg.readInt(0); + int amount = msg.readInt(1); + } + } + +Should this paradigm prove insufficient, +more ideas could be borrowed from the +[`org.vmmagic`](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.151.5253&rep=rep1&type=pdf) +package used by [Jikes RVM](http://jikesrvm.org/), +a research Java virtual machine itself written in Java. + +### Generating Java stubs with MIG + +Once the basic machinery is in place to interface with Mach, Java programs +have more or less equal access to the system functionality without resorting +to more JNI code. However, as illustrated above, this access is far from +convenient. + +As a solution I would modify MIG to add the option to output Java code. MIG +would emit a Java interface, a client class able to implement the interface +given a Mach port send right, an a server class which would be able to handle +incoming messages. The class diagram below, although it is by no means +complete or exempt of any problem, illustrates the general idea: + +[[gsoc2011_classes.png]] + +This structure is somewhat reminiscent of +[Java RMI](http://en.wikipedia.org/wiki/Java_remote_method_invocation) +or similar systems, +which aim to provide more or less transparent access to remote objects. +The exact way the Java code would be generated still needs to be determined, +but basically: + + * An interface, corresponding to the header files generated by MIG, would + enumerate the operations listed in a given .defs files. Method names would + be transformed to adhere to Java conventions (for instance, + `some_random_identifier` would become `someRandomIdentifier`). + * A user class, corresponding to the `*User.c` files, + would implement this interface by doing RPC over a given MachPort object. + * A server class, corresponding to `*Server.c`, would be able to handle + incoming messages using a user-provided implementation of the interface. + (Possibly, a skeleton class providing methods which would raise + `NotImplementedException`s would be provided as well. + Users would derive from this class and override the relevant methods. + This would allow them not to implement some operations, + and would avoid pre-existing code from breaking when new operations are + introduced.) + +In order to help with the implementation of servers, some kind of library +would be needed to associate Mach receive rights with server objects and to +handle incoming messages on dedicated threads, in the spirit of libports. +This would probably require support for port sets at the level of the Mach +primitives described in the previous section. + +When possible, operations involving the transmission of send rights +of some kind would be expressed in terms of the MIG-generated interfaces +instead of `MachPort` objects. +Upon reception of a send right, +a `FooUser` object would be created +and associated with the corresponding `MachPort` object. +If the received send right corresponds to a local port +to which a server object has been associated, +this object would be used instead. +This way, +subsequent operations on the received send right +would be handled as direct method calls +instead of going through RPC mechanisms. + +Some issues will still need to be solved regarding how MIG will convert +interface description files to Java interfaces. For instance: + + * `.defs` files are not explicitly associated with a type. For instance in + the example above, MIG would have to somehow infer that io_t corresponds + to `this` in the `Io` interface. + * More generally, a correspondence between MIG and Java types would have + to be determined. Ideally this would be automated and not hardcoded + too much. + * Initially, reply port parameters would be ignored. However they may be + needed for some applications. + +So the details would need to be flushed out during the community bonding +period and as the implementation progresses. However I’m confident that a +satisfactory solution can be designed. + +Using these new features, the example above could be rewritten as: + + import org.gnu.hurd.InitPorts; + import org.gnu.hurd.Io; + import org.gnu.hurd.IoUser; + + class Hello { + static void main(String argv[]) throws ... + { + Io stdout = new IoUser(InitPorts.getdport(1)); + String hello = “Hello, World!\n”; + + int amount = stdout.write(hello.getBytes(), -1); + + /* (A retCode corresponding to an error + would be signalled as an exception.) */ + } + } + +An example of server implementation would be: + + import org.gnu.hurd.Io; + import java.util.Arrays; + + class HelloIo implements Io { + final byte[] contents = “Hello, World!\n”.getBytes(); + + int write(byte[] data, int offset) { + return SOME_ERROR_CODE; + } + + byte[] read(int offset, int amount) { + return Arrays.copyOfRange(contents, offset, + offset + amount - 1); + } + + /* ... */ + } + +A new server object could then be created with `new IoServer(new HelloIo())`, +and associated with some receive right at the level of the ports management +library. + +### Base classes for common types of translators + +Once MIG can target Java code, and a libports equivalent is available, +creating new translators in Java would be greatly facilitated. However, +we would probably want to introduce basic implementations of file system +translators in the spirit of libtrivfs or libnetfs. They could take the form +of base classes implementing the relevant MIG-generated interfaces which +would then be derived by users, +or could define a simpler interface +which would then be used by adapter classes +to implement the required ones. + +I would draw inspiration from libtrivfs and libnetfs +to design and implement similar solutions for Java. + +### Deliverables + + * A hurd-java package would contain the Java code developed + in the context of this project. + * The Java code would be documented using javadoc + and a tutorial for writing translators would be written as well. + * Modifications to MIG would be submitted upstream, + or a patched MIG package would be made available. + +The Java libraries resulting from this work, +including any MIG support classes +as well as the class files built from the MIG-generated code +for the Mach and Hurd interface definition files, +would be provided as single `hurd-java` package for +Debian GNU/Hurd. +This package would be separate from both Hurd and Mach, +so as not to impose unreasonable build dependencies on them. + +I expect I would be able to act as its maintainer in the foreseeable future, +either as an individual or as a part of the Hurd team. +Hopefully, +my code would be claimed by the Hurd project as their own, +and consequently the modifications to MIG +(which would at least conceptually depend on the Mach Java package) +could be integrated upstream. + +Since by design, +the Java code would use only a small number of stable interfaces, +it would not be subject to excessive amounts of bitrot. +Consequently, +maintenance would primarily consist in +fixing bugs as they are reported, +and adding new features as they are requested. +A large number of such requests +would mean the package is useful, +so I expect that the overall amount of work +would be correlated with the willingness of more people +to help with maintenance +should I become overwhelmed or get hit by a bus. + + +## Timeline + +The dates listed are deadlines for the associated tasks. + + * *Community bonding period.* + Discuss, refine and complete the design of the Java bindings + (in particular the MIG and "libports" parts) + * *May 23.* + Coding starts. + * *May 30.* + Finish implementing pthread signal semantics. + * *June 5.* + Port OpenJDK + * *June 12.* + Fix the remaining problems with GCJ and/or OpenJDK, + possibly port Eclipse or other big Java packages. + * *June 19.* + Create the bindings for Mach. + * *June 26.* + Work on some kind of basic Java libports + to handle receive rights. + * *July 3.* + Test, write some documentation and examples. + * *July 17 (two weeks).* + Add the Java target to MIG. + * *July 24.* + Test, write some documentation and examples. + * *August 7 (two weeks).* + Implement a modular libfoofs to help with translator development. + Try to write a basic but non-trivial translator + to evaluate the performance and ease of use of the result, + rectify any rough edges this would uncover. + * *August 22. (last two weeks)* + Polish the code and packaging, + finish writing the documentation. + + +## Conclusion + +This project is arguably ambitious. +However, I have been thinking about it for some time now +and I'm confident I would be able to accomplish most of it. + +In the event multiple language bindings projects +would be accepted, +some work could probably be done in common. +In particular, +[ArneBab](http://www.bddebian.com/~hurd-web/community/weblogs/ArneBab/2011-04-06-application-pyhurd/) +seems to favor a low-level approach for his Python bindings as I do for Java, +and I would be happy to discuss API design and coordinate MIG changes with him. +I would also have an extra month after the end of the GSoC period +before I go back to school, +which I would be able to use to finish the project +if there is some remaining work. +(Last year's rewrite of procfs was done during this period.) + +As for the project's benefits, +I believe that good support for Java +is a must-have for the Hurd. +Java bindings would also further the Hurd's agenda +of user freedom by extending this freedom to more people: +I expect the set of developers +who would be able to write Java code against a well-written libfoofs +is much larger than +those who master the intricacies of low-level systems C programming. +From a more strategic point of view, +this would also help recruit new contributors +by providing an easier path to learning the inner workings of the Hurd. + +Further developments +which would build on the results of this project +include my planned [[experiment with Joe-E|objcap]] +(which I would possibly take on as a university project next year). +Another possibility would be to reimplement some parts +of the Java standard library +directly in terms of the Hurd interfaces +instead of using the POSIX ones through glibc. +This would possibly improve the performance +of some Java applications (though probably not by much), +and would otherwise be a good project +for someone trying to get acquainted with Hurd. + +Overall, I believe this project would be fun, interesting and useful. +I hope that you will share this sentiment +and give me the opportunity to spend another summer working on Hurd. + -- cgit v1.2.3 From 97ef5d15ef5e44806b92da486c5f06311db14727 Mon Sep 17 00:00:00 2001 From: Thomas Schwinge Date: Wed, 15 Jun 2011 19:01:24 +0200 Subject: user/jkoenig/java: Integrate most of the action items from the discussion page. --- user/jkoenig/java.mdwn | 91 +++++++++++++++++++++++++++++++- user/jkoenig/java/discussion.mdwn | 108 -------------------------------------- 2 files changed, 90 insertions(+), 109 deletions(-) (limited to 'user/jkoenig/java') diff --git a/user/jkoenig/java.mdwn b/user/jkoenig/java.mdwn index 90f51028..fcd316b7 100644 --- a/user/jkoenig/java.mdwn +++ b/user/jkoenig/java.mdwn @@ -38,7 +38,7 @@ I have submitted [preliminary patches](http://lists.gnu.org/archive/html/bug-hurd/2011-05/msg00182.html) for global signal dispositions, which I'm currently testing. -I have since fixed a few thinks and implemented `SA_SIGINFO` +I have since fixed a few things and implemented `SA_SIGINFO` (which is required by OpenJDK.) My latest code is available on [github](http://github.com/jeremie-koenig/glibc/commits/master-beware-rebase), @@ -56,6 +56,7 @@ at which point we will alias the interim version to the new one in debian packages. I have modified libc0.3 to include a `deb-symbols(5)` file +(alternatively see ) so that we get an accurate libc dependency in `hurd` and other packages when the symbols in question are pulled in. @@ -71,6 +72,28 @@ I expect only the last patch (implement global dispositions) will change, and new ones will be added on top of it. +##### Open Items + + * Test patches: in progress, [[jkoenig]], Svante. More volunteers welcome, + of course. + + * If [[jkoenig]] thinks it's mature enough: should ask Samuel to test this + (that is, only the refactoring patches for starters?) on the buildds. + + * Get patches reviewed (Roland?), and integrated into official sources: [!] + [[tschwinge]]. + + * Documentations bits (from [[proposal]] and elsewhere) should probably be + moved either into the appropriate glibc or Hurd documentation + files/reference manuals, or to [[glibc/signal]]. + + * libthreads (cthreads) integration. + + * [[tschwinge]] suggests to leave them as-is? + + * [[libpthread]] integration. + + ### Port OpenJDK As suggested by [[tschwinge]], I have targeted OpenJDK 7 at first. @@ -107,8 +130,74 @@ although the current toolchain issues have so far prevented me from testing it. +##### Open Items + + * They seem to have a rather heavy-weight process for such projects: confer + , + for example. Do we need this, too? + + * Eclipse + + OK for testing -- but I'd very much hope that it *just works* as soon as we + provide the required Java platform. But it may perhaps have some + Linux-specifics (needlessly?) in its basement. Is it available for Debian + GNU/kFreeBSD already? + + ### Java bindings for Mach + +#### Plans + (just started.) +##### Open Items + + * [[tschwinge]] has to read about RMI and CORBA. + + * MIG + + * Hacking [[microkernel/mach/MIG]] shouldn't be too difficult. + + * (Unless you want to make MIG's own code (that is, not the generated + code, but MIG itself) look a bit more nice, too.) ;-) + + * There are also alternatives to MIG. If there is interest, the following + could be considered: + + * FLICK ([[!GNU_Savannah_task 5723]]). [[tschwinge]] has no idea yet if + there would be any benefits over MIG, like better modularity (for the + backends)? If we feel like it, we could spend a little bit of time on + this. + + * For [[microkernel/Viengoos]], Neal has written a RPC stub generator + entirely in C Preprocessor macros. While this is obviously not + directly applicable, perhaps we can get some ideas from it. + + * Anything else that would be worth having a look at? (What are other + microkernels using?) + + * `mach_msg` + + * Seems like the right approach to [[tschwinge]], but he hasn't digested + all the pecularities yet. Will definitely need more time. + + +## Postponed + +Might get back to these as time/interest permits. + + +### GCJ + + * [[tschwinge]] has the feeling that Java in GCC (that is, GCJ) is mostly + dead? (True?) + + * Thus perhaps not too much effort should be spent with it. + + If the POSIX threads signal semantics makes it going, then great, otherwise + we should get a feeling what else is missing. + + +### Joe-E. diff --git a/user/jkoenig/java/discussion.mdwn b/user/jkoenig/java/discussion.mdwn index 0131d8d5..266a7bcc 100644 --- a/user/jkoenig/java/discussion.mdwn +++ b/user/jkoenig/java/discussion.mdwn @@ -56,114 +56,6 @@ one person's summer.) Such bits could be moved to [[open_issues]] pages, either new ones or existing ones, as applicable. -# POSIX Threads Signal Semantics - - * Great! [[tschwinge]] had a brief look, and should have a deeper one. - - * If [[jkoenig]] thinks it's mature enough: should ask Samuel to test this - (that is, only the refactoring patches for starters?) on the buildds. - - * Then: should ask Roland to review. - - * Documentations bits should probably be moved to [[glibc/signal]]. - - -## libthreads (cthreads) Integration - - * [[tschwinge]] suggests to leave them as-is? - - -## [[libpthread]] integration - - * To be done. - - -# Java - - * [[tschwinge]] has to read about RMI and CORBA. - - -# Joe-E - - * For later. - - -# GCJ - - * [[tschwinge]] has the feeling that Java in GCC (that is, GCJ) is mostly - dead? (True?) - - * Thus perhaps not too much effort should be spent with it. - - If the POSIX threads signal semantics makes it going, then great, otherwise - we should get a feeling what else is missing. - - -# OpenJDK - - * All in all, [[tschwinge]] has the feeling that a working OpenJDK will be - more useful/powerful than GCJ. - - * We need to get a feeling how difficult such an OS port will be. - - * [[jkoenig]] suggests OpenJDK 6 -- should we directly go for version 7 - instead? - - * What are the differences (regarding the OS port) between the two - versions? Or this there something even more recent to be worked upon, - for new OS ports? - - * Perhaps the different versions' OS port specific stuff is not at - all very different, so that both v6 and v7 could be done? - - * They seem to have a rather heavy-weight process for such projects: confer - , - for example. Do we need this, too? - - -# Eclipse - -OK for testing -- but I'd very much hope that it *just works* as soon as we -provide the required Java platform. - - -# Java Bindings - - -## Design Principles - - * Generally ack. - - -### MIG - - * Hacking [[microkernel/mach/MIG]] shouldn't be too difficult. - - * (Unless you want to make MIG's own code (that is, not the generated - code, but MIG itself) look a bit more nice, too.) ;-) - - * There are also alternatives to MIG. If there is interest, the following - could be considered: - - * FLICK ([[!GNU_Savannah_task 5723]]). [[tschwinge]] has no idea yet if - there would be any benefits over MIG, like better modularity (for the - backends)? If we feel like it, we could spend a little bit of time on - this. - - * For [[microkernel/Viengoos]], Neal has written a RPC stub generator - entirely in C Preprocessor macros. While this is obviously not - directly applicable, perhaps we can get some ideas from it. - - * Anything else that would be worth having a look at? (What are other - microkernels using?) - - -### `mach_msg` - - * Seems like the right approach to [[tschwinge]], but hasn't digested all the - pecularities yet. Will definitely need more time. - - # GSoC Site Discussion * Discussion items from -- cgit v1.2.3 From f2cbce0dc26005f74aeb5ca1011f4923bc3aaaba Mon Sep 17 00:00:00 2001 From: Thomas Schwinge Date: Fri, 8 Jul 2011 22:35:03 +0200 Subject: user/jkoenig/java/java-access-bridge: New. --- user/jkoenig/java.mdwn | 2 + user/jkoenig/java/java-access-bridge.mdwn | 78 +++++++++++++++++++++++++++++++ 2 files changed, 80 insertions(+) create mode 100644 user/jkoenig/java/java-access-bridge.mdwn (limited to 'user/jkoenig/java') diff --git a/user/jkoenig/java.mdwn b/user/jkoenig/java.mdwn index fe391582..7df1dd73 100644 --- a/user/jkoenig/java.mdwn +++ b/user/jkoenig/java.mdwn @@ -219,6 +219,8 @@ have so far prevented me from testing it. and the like only, so for now the goal should be to lose some functionality by removing/avoiding this dependency. + * [[java-access-bridge]] (not critical; JVM appears to work without) + * They seem to have a rather heavy-weight process for such projects: confer , for example. Do we need this, too? diff --git a/user/jkoenig/java/java-access-bridge.mdwn b/user/jkoenig/java/java-access-bridge.mdwn new file mode 100644 index 00000000..6f860709 --- /dev/null +++ b/user/jkoenig/java/java-access-bridge.mdwn @@ -0,0 +1,78 @@ +[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_porting]] + +Debian's *openjdk-7-jre* package depends on *libaccess-bridge-java-jni* (source +package: *java-access-bridge*). + +The latter one has *openjdk-6-jdk* as a build dependency, but that can be +hacked around: + + # ln -s java-7-openjdk /usr/lib/jvm/java-6-openjdk + +Trying to build it: + + $ LD_LIBRARY_PATH=/usr/lib/jvm/java-7-openjdk/jre/lib/i386/jli dpkg-buildpackage -b -uc -d + [...] + make[3]: Entering directory `/media/erich/home/thomas/tmp/libaccess-bridge-java-jni/java-access-bridge-1.26.2/idlgen' + /usr/lib/jvm/java-6-openjdk/bin/idlj \ + -pkgPrefix Bonobo org.GNOME \ + -pkgPrefix Accessibility org.GNOME \ + -emitAll -i /usr/share/idl/bonobo-activation-2.0 -i /usr/share/idl/at-spi-1.0 -i /usr/share/idl/bonobo-2.0 \ + -fallTie /usr/share/idl/at-spi-1.0/Accessibility.idl + /usr/share/idl/at-spi-1.0/Accessibility_Collection.idl (line 66): WARNING: Identifier `object' collides with a keyword; use an escaped identifier to ensure future compatibility. + boolean isAncestorOf (in Accessible object); + ^ + /usr/share/idl/at-spi-1.0/Accessibility_Component.idl (line 83): WARNING: Identifier `Component' collides with a keyword; use an escaped identifier to ensure future compatibility. + interface Component : Bonobo::Unknown { + ^ + Exception in thread "main" java.lang.AssertionError: Platform not recognized + at sun.nio.fs.DefaultFileSystemProvider.create(DefaultFileSystemProvider.java:71) + at java.nio.file.FileSystems$DefaultFileSystemHolder.getDefaultProvider(FileSystems.java:108) + at java.nio.file.FileSystems$DefaultFileSystemHolder.access$000(FileSystems.java:89) + at java.nio.file.FileSystems$DefaultFileSystemHolder$1.run(FileSystems.java:98) + at java.nio.file.FileSystems$DefaultFileSystemHolder$1.run(FileSystems.java:96) + at java.security.AccessController.doPrivileged(Native Method) + at java.nio.file.FileSystems$DefaultFileSystemHolder.defaultFileSystem(FileSystems.java:95) + at java.nio.file.FileSystems$DefaultFileSystemHolder.(FileSystems.java:90) + at java.nio.file.FileSystems.getDefault(FileSystems.java:176) + at sun.util.calendar.ZoneInfoFile$1.run(ZoneInfoFile.java:489) + at sun.util.calendar.ZoneInfoFile$1.run(ZoneInfoFile.java:480) + at java.security.AccessController.doPrivileged(Native Method) + at sun.util.calendar.ZoneInfoFile.(ZoneInfoFile.java:479) + at sun.util.calendar.ZoneInfo.getTimeZone(ZoneInfo.java:658) + at java.util.TimeZone.getTimeZone(TimeZone.java:559) + at java.util.TimeZone.setDefaultZone(TimeZone.java:656) + at java.util.TimeZone.getDefaultRef(TimeZone.java:623) + at java.util.TimeZone.getDefault(TimeZone.java:610) + at java.text.SimpleDateFormat.initializeCalendar(SimpleDateFormat.java:682) + at java.text.SimpleDateFormat.(SimpleDateFormat.java:619) + at java.text.DateFormat.get(DateFormat.java:772) + at java.text.DateFormat.getDateTimeInstance(DateFormat.java:547) + at com.sun.tools.corba.se.idl.toJavaPortable.Util.writeProlog(Util.java:1139) + at com.sun.tools.corba.se.idl.toJavaPortable.Skeleton.writeHeading(Skeleton.java:145) + at com.sun.tools.corba.se.idl.toJavaPortable.Skeleton.generate(Skeleton.java:102) + at com.sun.tools.corba.se.idl.toJavaPortable.InterfaceGen.generateSkeleton(InterfaceGen.java:159) + at com.sun.tools.corba.se.idl.toJavaPortable.InterfaceGen.generate(InterfaceGen.java:108) + at com.sun.tools.corba.se.idl.InterfaceEntry.generate(InterfaceEntry.java:110) + at com.sun.tools.corba.se.idl.toJavaPortable.ModuleGen.generate(ModuleGen.java:75) + at com.sun.tools.corba.se.idl.ModuleEntry.generate(ModuleEntry.java:83) + at com.sun.tools.corba.se.idl.Compile.generate(Compile.java:324) + at com.sun.tools.corba.se.idl.toJavaPortable.Compile.start(Compile.java:169) + at com.sun.tools.corba.se.idl.toJavaPortable.Compile.main(Compile.java:146) + make[3]: *** [org/GNOME/Accessibility/Accessible.java] Error 1 + make[3]: Leaving directory `/media/erich/home/thomas/tmp/libaccess-bridge-java-jni/java-access-bridge-1.26.2/idlgen' + make[2]: *** [all-recursive] Error 1 + make[2]: Leaving directory `/media/erich/home/thomas/tmp/libaccess-bridge-java-jni/java-access-bridge-1.26.2/idlgen' + make[1]: *** [all-recursive] Error 1 + make[1]: Leaving directory `/media/erich/home/thomas/tmp/libaccess-bridge-java-jni/java-access-bridge-1.26.2' + make: *** [debian/stamp-makefile-build] Error 2 + dpkg-buildpackage: error: debian/rules build gave error exit status 2 -- cgit v1.2.3 From 9f5e3555f8812ebe4447b7a5519988b4b61275bc Mon Sep 17 00:00:00 2001 From: Thomas Schwinge Date: Fri, 15 Jul 2011 22:47:52 +0200 Subject: user/jkoenig/java/discussion: IRC discussion, 2011-07-13. --- user/jkoenig/java/discussion.mdwn | 454 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 454 insertions(+) (limited to 'user/jkoenig/java') diff --git a/user/jkoenig/java/discussion.mdwn b/user/jkoenig/java/discussion.mdwn index 266a7bcc..f16d7678 100644 --- a/user/jkoenig/java/discussion.mdwn +++ b/user/jkoenig/java/discussion.mdwn @@ -8,6 +8,11 @@ Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled [[GNU Free Documentation License|/fdl]]."]]"""]] +[[!toc]] + + +# General + Some [[tschwinge]] comments regarding your proposal. Which is very good, if I may say so again! :-) @@ -70,3 +75,452 @@ either new ones or existing ones, as applicable. * We should probaby open up a *languages for Hurd* section on the web pages ([[!taglink open_issue_documentation]]). + + +# IRC, freenode, #hurd, 2011-07-13 + +[[!tag open_issue_documentation]] + + Yes, I guess so. Maybe start investigating mig because it may + have repercussions on what the best approach would be for some aspects of + the Mach bindings. + I still think that making MIG emit Java code is not too + difficult, once you have the required Java infrastructure (like what + you're writing at the moment). + On the other hand, if there's another approach that you'd like + to use, I'm not trying to force using MIG. + i still have a problem understanding your approach + at which level are your bindings located ? + I expect mig it will be the easiest route, but of course possibly + it won't. + jkoenig: Yeah, be give some high-level to low-level overview? + ok, so + at the very core, low-level, we have a very thin amount of JNI + code to access (proper) system calls. + by "proper" I mean things like mach_task_self, mach_msg and + mach_reply_port, which are actually system calls rather than RPCs to the + kernel. + right + at this level, we manipulate port names as integers, and the + message buffers for mach_msg are raw ByteBuffers (from the java.nio + package) + actually, so-called /direct/ ByteBuffers, which are backed by + memory allocated outside of the Java heap, rather than as a byte[] array + we can retreive the pointer from the JNI code and use the buffer + directly. + (so, good for performance and it's also portable.) + ok + i'm more interested in the higher level bindings :) + ok so, higher up. + design goal from my proposal: "the memory safety of Java should + be maintained and extended to Mach primitives such as port names and + out-of-line memory regions" + so integer port names are not "safe" in the sense that they can + be forged and misused in all kinds of way + which is why I have a layer of Java code whose job is to wrap + this kind of low-level Mach stuff into safe abstractions + and ideally the user should only use these safe abstractions. + (Not to restrict the programmer, but to help him write correct + code.) + right. + so you can't use mach RPCs directly + tschwinge, also to actually restrict them, in a Joe-E / + object-capability context, but that's not the primary concern right now + ;-) + or you force your wrappers to have these abstractions as input + braunr, well, actually at this level you still have Mach RPC + but for instance, port names are encapsulated into "MachPort" + objects which ensure they are handled correcly + As I understand it, you use these abstractions to prepare a + usual mach_msg message, and then invoke mach_msg. + ok + and message buffers are wrapped into "MachMsg" objects which both + help you write the messages into the ByteBuffer and prevent you from + doing funky stuff + and ensure the ports which you send/receive/pseudo-receive after + an error/... are deallocated as required, etc. + what's the interface to use IPC ? + Is MIG doing that, too, I think? (And antrik once found some + error there, which is still to be reviewed...) + braunr, so basically as a user you would be free to use either + one of these layers, or to use MIG-generated classes which would + construct and exchange messages for you using the second (safe) layer. + ok, let's just finish with the low level layer before going + further please + tschwinge, MIG does some type checking on the received message + and saves you the trouble of constructing/parsing them yourself, but I'm + not sure about how mach_msg errors are handled + what are the main methods of MachMsg for example ? + braunr, you may want to have a look at + http://jk.fr.eu.org/hurd-java/doc/html/classorg_1_1gnu_1_1mach_1_1MachMsg.html + right, sorry + grabbed the code at work and forgot here + and also + https://github.com/jeremie-koenig/hurd-java/blob/master/HelloMach.java + which uses it + but roughly, you'd use setRemotePort, setLocalPort, setId to + write your message's header + then use one of the putFoo() methods to add data items to the + message + ok, the mapping with the low level C interface is very clear + that's good for me + the putFoo() methods would write the appropriate type + descriptors, then the actual data. + we can go on with the MiG part if you want :) + right, + so here you may want to look at the UML class diagram from + http://www.bddebian.com/~hurd-web/user/jkoenig/java/proposal/ + so in the C case, mig generates 3 files + a header file which has the prototypes of the mig-generated + stubs, + a *User.c which has their actual implementation + and a *Server.c which handles demultiplexing the incoming + messages and helps with implementing servers. + so we would do something along these lines, more or less: + mig would generate the code for a Java interface in lieu of the + *.h file. + a generated FooUser class would implement this interface by doing + RPC + (so basically you would pass a MachPort object to the + constructor, and then you could use the resulting object to do RPC with + whatever is on the other end) + and the generated FooServer class would do the opposite, + ok + issues with threads ? + you would pass an object implementing the Foo interface to the + constructor, + i'm guessing the demux part may have to create threads, right ? + and the resulting object would handle messages by using the + object you passed. + braunr, right, so that would be more a libports kind of code, + the libports-like library, i see + to which you could pass Server objects (for instance the + FooServer above), and it would handle incoming messages. + how is message content mapped to a java interface ? + this would be determined from the .defs files and MIG would + generate the appropriate code, hopefully. + so the demux part would handle rpc integer identifiers ? + right. + but hm + also mapping .defs files to Java interfaces might prove to be + tricky. data types conversion and all + tschwinge: my mamory is rather hazy. IIRC the issue was that the + MIG-generated stubs deallocate out-of-line port arrays after the + implementation returns, before returning to the dispatcher + i'll just overlook this specific implementation detail + but we could use some annotation-based system if we need to + provide more information to generate the java code. + but the Hurd (or rather glibc) RPC handling also automatically + deallocates everything if an error occurs + so I changed the MIG code to deallocate only when no error occurs + jkoenig: ok, we'll talk about that when there is more progress and + you have a better view of the problem + at that time I was pretty sure that this is a correctly working + solution, but it always seemed questionable conceptually... however, I + wasn't able to come up with a better one, and nobody else commented on it + antrik: shouldn't the hurd be changed not to deallocate something + it didn't allocate in the first place ? + braunr: no, the server has to deallocate stuff before returning to + the client. the request message is destroyed before returning the reply. + jkoenig, braunr: That's what I had in mind where MIG might be a + bit awkward. Then we can indeed either add annotations to the .defs + files, or reproduce them in some other format. That's some work, but + it's mostly a one-time work. + After all, the RPC interface is a binary one, and there may be + more than one API for creating these messages, etc. + jkoenig: actually, at least in the Hurd, server-side and + client-side headers are separate -- so MIG actually creates four files + tschwinge, wrt to annotations I was more thinking about Java + ones, such as: @MIGDefsFile("mach/task.defs") @MIGCType("task_t") public + interface Task { } + antrik, oh, ok, it makes sense. + jkoenig: anything else ? + braunr, nothing that I can think of + ok + tschwinge: I think it would be a *very* bad idea to introduce + redundancy regarding RPC definitions + thanks for the tour :) + (the _request.defs/_reply.defs mess is bad enough...) + did I speak about the "Unsafe" pseudo-exception? that's + interesting :-) + jkoenig: Also, virtual memory abstractions? + jkoenig: you didn't + antrik: Well, then we could create some other super-format. + But that's just a detail IMO. + ok, so wrt virtual memory, a page we received can be wrapped with + some JNI help into a (direct) ByteBuffer object. + deallocating sent pages will be tricky, though. + antrik: To put it this way: for me the .defs files are just one + way of expressing the RPC interfaces' contracts. (At the same time, they + happen to be the actual reference for these, too. But the specification + itself could just as well be a textual one.) + on approach I've been thinking about would be to "wrap" the + ByteBuffer object into an object which has the sole reference to it, so + that when it's deallocated the reference can be replaced with "null", and + further attempts to access the buffer would throw exceptions. + sounds reasonable + but that's still in flux in my head, we may end up needing our + own implementation of ByteBuffer-like objects. + The problem being that there is no mechanism to ``revoke'' an + object once a reference to it has been shared. + right. + A wrapper is one possibility indeed. + tschwinge: they are called interface *definitions* for a reason + :-) + This is a very similar problem as with capabilities when there + is no revoke operation for these, too. + antrik: Yes, because they define MIG's input. :-P + Isn't that what is called a membrane in the capability world? + I do not say that we have to consider the format of the .defs to + be set in stone; but I do insist on using a canonical machine-parsable + source for all language bindings + attenuation + tschwinge, you mean the revokable proxy contruct ? (It's the same + principle indeed) + A common design pattern in object-capability systems: given + one reference of an object, create another reference for a proxy object + with certain security restrictions, such as only permitting read-only + access or allowing revocation. The proxy object performs security checks + on messages that it receives and passes on any that are allowed. Deep + attenuation refers to the case where the same attenuation is applied + transitively to any + objects obtained via the original attenuated object, + typically by use of a "membrane". + http://en.wikipedia.org/wiki/Object-capability_model + Yes. + Good. I understood something. ;-) + antrik: OKAY! :-P + jkoenig: And hopefully the JVM will optimize away all the + additional indirection... :-D + jkoenig: Is there anything more to say about the VM layer? + tschwinge, "hopefully", yes :-) + Like, the data that I'm sharing -- is it untyped, isn't it? + tschwinge, you mean that within the received/sent pages ? + Yes. + But that'S how it is, indeed. + well actually the type descriptor should indicate what they + contain. + I cannot trust anything I receive from externally. + it's most often used for MACH_MSG_TYPE_CHAR items I guess, and it + will be type checked when retreive + Yeah, and that then just *is* arbitrary data, like a block read + from a disk file. + you would have something like: ByteBuffer + MachMsg.getBuffer(MachMsg.Type expected), and MachMsg would check the + type descriptor against that which you specified + Or a packet transmitted over the network. + OK, yes. + jkoenig: in theory ints should be used quite often too. the whole + purpose of the type descriptors is to allow byte order swapping when + messages are passed between hosts with different architecture... + tschwinge, right, except for out-of-line port arrays, which need + to be handled differently obviously. + (which is totally irrelevat for our purposes -- especially since + the actual network IPC code doesn't exist anymore ;-) ) + antrik, oh, interesting + Yes, that was one original idea. + actually my litmus test for what the bindings should be, is you + should be able to implement such a proxy in Java :-) + antrik: And hey, you now have processors that can switch + between different modes during runtime... :-) + (although arguably that's a little bit ambitious) + tschwinge: there should be bits in page tables to indicate the + endianness to use on a page .. :) + Hehe! + jkoenig: Don't worry -- you're already known for ambitious + projects. One more can't hurt. + Also, actually the word size is not something that I've been able + to abstract so far, so I'll be hardcoding little-endian 32 bits for now. + why is that ? + some of the Hurd RPC break the idea anyways BTW + the org.vmmagic package (from Jikes RVM and JNode) could help + with that, but GCJ does not support it unfortunately (not sure about + OpenJDK) + braunr, Java does not allow us to define new unboxed types + jkoenig: does it have its own definition of the word size ? + braunr, nope. + (although, maybe, and also we could use JNI to query it) + even if virtual, i'd expect a machine to have such a defnition + braunr, maybe it has, but basically in Java nothing depends on + the word size + 'int' is 32 bits, 'long' is 64 and that's it. + oh right, i remember most types are fixed size, right ? + right. + if not all + now Jikes RVM's "org.vmmagic" provides an interface to defined + new unboxed types which can depend on the actual word size, but Jikes RVM + is its own JVM so obviously they can use and provide whatever extensions + they need :-) + (but maybe they've implemented them in OpenJDK for bootstrap + purposes, I'm not sure) + I'm missing this detail: where does the word size come into + play here? + anyway, I _could_ indiscriminately use 'long' for port names, and + sparkle the code with word size tests but that would be very clumsy + jkoenig: port names are actually ints :/ + tschwinge, the actual format of the message header and type + descriptors, for instance. + jkoenig: ok, got your point + braunr, by 'long' I mean 64-bits integers (which they are on + 64-bits machines I think?) + :) + jkoenig: port names are as large as the word size + but in C at least, they're int, not long + it doesn't change many things, but you get lots of warnings if you + try with a long :) + What is the reason that port names are an + architecture-dependent word size's width, and not simply 32 bit? + "4 billions of port names should be enough for everyone" :-) + tschwinge: an optimization is to use them as pointers in the + kernel + tschwinge: the machine's native word size is what it can process + most efficiently, and what should be used for most normal + operations... it makes sense to define stuff as int, except for network + communication + jkoenig: Well, yeah, but if you want to communicate with a + peer, you have to agree on the maximum number anyway (not for port names, + though, which are local). + antrik: int isn't the word size everywhere + antrik: the most common type matching the word size is long, at + least on ILP32/LP64 data models + braunr: that's just because some idiots assumed int would always + be 32 bits, and consequently when 64 architectures came up the compiler + guys chickened out ;-) + without int, you wouldn't have a 32 bits type + that's not true for all architectures and/or operating systems + though AFAIK + or a 16 bits one + antrik: windows guys got even more scared, so windows 64 is LLP64 + BTW, I haven't checked, but it's quite possible that 32 bit + numbers are actually preferable even on AMD64... + jkoenig: So, back on track. :-) + jkoenig: You didn't find anything yet in Mach's VM interfaces + as well a MemoryObject, etc., that can't be used/implemented in the Java + world? + antrik: they consume less memory, but don't have much effect on + performance + tschwinge, once we have the basic system calls and the + corresponding abstractions in place, I don't think anything else + fundamentally problematic could possibly show up + braunr: if you really *need* a type of a certain bit size, you + should use stdint types. so not having a 16 or 32 bit type in the + short/int/long canon is *not* an excuse + jkoenig: That speaks for the Mach designers! + antrik: right + tschwinge, on trick is that for instance, mach_task_self would + still be unsafe even if it returned a nicely wrapped Task object, because + you could still wreck your own address space and threads with it. So we + would need the "attenuation" pattern mentionned above to provide a safe + one. + (which would disallow thinks such as the port/thread/vm calls) + jkoenig: you mentioned the unsafe pseudo exception earlier + braunr, right, so the issue is with distinguishing safe from + unsafe methods + braunr: BTW, the Windows guys actually broke a lot of stuff by + fixing long at 32 bits -- this way long doesn't match size_t and pointer + types anymore, which was an assumption that was true for pretty much any + system so far... + jkoenig: Yes. (And again hope for the JVM to optim...) + antrik: that's right :) + antrik: that's LLP64 + antrik: long long and pointers + braunr, so basically the idea is that unsafe methods are declared + as "throws Unsafe" + the effect is that if you use such a method you must either + "throw Unsafe" yourself, + or if you're building a safe abstraction on top of Unsafe + methods, you'll "catch" the "exception" in question to tell the compiler + that it's okay. + it's more or less inspired from the "semantic regimes" idea from + the org.vmmagic paper which is referenced in my original proposal, + only implementing by hijacking the exception checking machinery, + which has a behaviour similar to what we want. + ok + but hmm this seems pretty normal, what's the tricky part ? :) + braunr: The idea is that the programmer explicitly has to + acknowledge if he'S using an unsafe interface. + tschwinge: sounds pretty normal too + braunr, the trick is that you would not usually declare + exceptions which are never actually thrown (and actually since the + compiler does not know it's never thrown, I need to work around it in a + few places) + oh, ok + jkoenig: that's interesting indeed + braunr, the org.vmmagic paper provides an example which uses some + annotations called @UncheckedMemoryAccess and @AssertSafe to the same + effect (which is kind of cleaner), but it would be a headache to + implement without help from the compiler I think (as far as I can tell + the annotation processor would have to inspect the bytecode) + but hm + what's the true problem about this ? + (the paper advocates "high-level low-level programming" and is a + very interesting read I think, + http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.151.5253&rep=rep1&type=pdf, + for what it's worth) + what's wrong if you just declare your methods unsafe and don't + alter anything else ? + Yes, I read it and it is interesting. Unfortunately, it seems + I forgot most of it again... + braunr, declare? alter? + you mean just tag them with an annotation? + just stating a method "throws Unsafe" + braunr, well some compiler will output a warning because they can + tell there's no way the method is going to throw such an exception. + and then some other compiler will complain that my + @SuppressWarnings("unused") does not serve any purpose to them :-) + also, when initializing final fields, I need to work around the + fact that the compiler thinks "Unsafe" might be thrown. + see for instance MachPort.DEAD + jkoenig: ok + braunr, but I'm more than willing to accept this in exchange for + a clear, compiler-enforced materialization of the border between safe an + unsafe code. + actually another question I have is the amount of static typing I + should add to the safe version, for instance should I subclass MachPort + into MachSendRight, MachReceiveRight and so on. I don't want to depart + from the C inteface too much but it could be useful. + jkoenig: can't answer that :) + jkoenig: keep them in mind for later i think + jkoenig: What's the safety concern w.r.t. having MachPort (not) + final? + tschwinge, actually I'm partly wrong in that we only need name() + and a couple other methods to be final + jkoenig: That's what I was thinking. :-) + I though I'm missing something here. + tschwinge, the idea is that the user (ie., the adversary :-) + could extend MachPort and inject their own fake port name into messages + by overriding name() or clear() + Yeah, but if these are final, that's not possible. + right. + And that *should* be enough, I think. + Unless I'm missing something. + I don't think so. Also I hope it is, because as mentionned above + there might be some value in subclassing MachPort. + Yep. + incidentally, declaring the class or the method final will allow + the JVM to inline them I think. + It will help the JVM, yes. It can also figure that out without + final, though. (And may have to de-optimize the code again in case there + are additional classes loaded during run-time.) + jkoenig: The reference counting in MachPort. I think I'm + beginning to understand this. + oh ok + tschwinge, yes the javadoc is maybe a bit obscure so far. + but basically you don't want the port name you acquire to become + invalid before you're done using it. + But how is this different from the C world? + here my goal is to provide some guarantees if you use only safe + methods + like, you can't forge a port name and things like that + so basically it should never be possible to include an invalid + port name in a message if you use only safe methods. + Ah, I see! + Now that does make sense. + but the mechanism in itself is similar to the Hurd port cells and + user_link structures + It's again ``only'' helping the programmer. + right, no object-capability ulterior motives :-) + another assumption which the javadoc does not state yet it that + basically there should be exactly one MachPort object for each mach-level + port name reference (in the sense of mach_port_mod_refs) + Yes, I figured out that bit. -- cgit v1.2.3