diff options
Diffstat (limited to 'microkernel/mach')
| -rw-r--r-- | microkernel/mach/concepts.mdwn | 27 | ||||
| -rw-r--r-- | microkernel/mach/documentation.mdwn | 6 | ||||
| -rw-r--r-- | microkernel/mach/external_pager_mechanism.mdwn | 14 | ||||
| -rw-r--r-- | microkernel/mach/ipc.mdwn | 19 | ||||
| -rw-r--r-- | microkernel/mach/memory_object.mdwn | 31 | ||||
| -rw-r--r-- | microkernel/mach/message.mdwn | 31 | ||||
| -rw-r--r-- | microkernel/mach/mig.mdwn | 33 | ||||
| -rw-r--r-- | microkernel/mach/mig/documentation.mdwn | 14 | ||||
| -rw-r--r-- | microkernel/mach/mig/gnu_mig.mdwn | 12 | ||||
| -rw-r--r-- | microkernel/mach/port.mdwn | 114 | ||||
| -rw-r--r-- | microkernel/mach/rpc.mdwn | 16 | ||||
| -rw-r--r-- | microkernel/mach/task.mdwn | 23 | ||||
| -rw-r--r-- | microkernel/mach/thread.mdwn | 37 | ||||
| -rw-r--r-- | microkernel/mach/virtual_address_space.mdwn | 36 |
14 files changed, 328 insertions, 85 deletions
diff --git a/microkernel/mach/concepts.mdwn b/microkernel/mach/concepts.mdwn index 04dbb1c6..a9e8897d 100644 --- a/microkernel/mach/concepts.mdwn +++ b/microkernel/mach/concepts.mdwn @@ -1,6 +1,25 @@ -[[Mach]] is a first-generation [[microkernel]]. Mach's basic abstractions -include [[address_space]]s in the form of [[task]]s, execution contexts in the -form of [[thread]]s, [[IPC]], [[capabilities|capability]] in the form of [[port]]s, and -[[memory_object]]s, which enable Mach's [[external_pager_mechanism]]. +[[!meta copyright="Copyright © 2002, 2003, 2007, 2010 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]]."]]"""]] + +[[Mach]] is a first-generation [[microkernel]]. + +Mach's basic abstractions include [[virtual_address_space]]s in the form of +[[task]]s, execution contexts in the form of [[thread]]s, [[IPC]], +[[capabilities|capability]] in the form of [[port]]s, and [[memory_object]]s, +which enable Mach's [[external_pager_mechanism]]. + +Controlling [[task]]s, their [[virtual_address_space]], [[thread]]s, and other +system objects in Mach is implemented by using [[port]]s, as opposed to other +[[kernel]]s' [[system_call]] interface: almost all of the Mach API is +implemented by sending [[message]]s to [[port]]s. Device drivers that reside +in kernel space are controlled by ports, too. Mach's [[API]] is well-[[documented|documentation]]. diff --git a/microkernel/mach/documentation.mdwn b/microkernel/mach/documentation.mdwn index fc6e59c2..4c6702aa 100644 --- a/microkernel/mach/documentation.mdwn +++ b/microkernel/mach/documentation.mdwn @@ -6,8 +6,10 @@ 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + + * Mach's [[concepts]]. * [*Meet Mach* by James Scott](http://beefchunk.com/documentation/macosx-programming/Meet_Mach.pdf), diff --git a/microkernel/mach/external_pager_mechanism.mdwn b/microkernel/mach/external_pager_mechanism.mdwn index 2040f4ba..e169495a 100644 --- a/microkernel/mach/external_pager_mechanism.mdwn +++ b/microkernel/mach/external_pager_mechanism.mdwn @@ -9,18 +9,16 @@ 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]]."]]"""]] -Mach provides a so-called external pager [[mechanism]]. This +Mach provides a so-called *external pager [[mechanism]]*. This mechanism serves to separate *managing memory* from *managing -content*. Mach does the former while [[user_space]] [[task]]s do the +content*. Mach does the former while user-space processes do the latter. # Introduction -In Mach, a [[task]]'s [[address_space]] consists of references -to [[memory_object]]s. A memory object is [[designated|designation]] using -a [[port]] (a port is just a [[capability]]) and -implemented by a normal [[process]]. +In Mach, a [[task]]'s [[virtual_address_space]] consists of references to +[[memory_object]]s. To associate a memory object with a portion of a task's address space, `vm_map` is invoked on a capability designating @@ -29,7 +27,7 @@ and the offset at which to install it. (The first time a task maps an object, Mach sends an initialization message to the server including a control capability, which it uses to supply pages to the kernel.) This is essentially -the same as mapping a file into an address space on [[Unix]] +the same as mapping a file into an address space on [[UNIX]] using `mmap`. When a task [[faults|page_fault]], Mach checks to see if there is a memory @@ -86,7 +84,7 @@ structures to manage the mapping and then invokes the mappings in the client's address space and then replies to the `vm_map` RPC indicating success. -There is nothing stopping others from playing "the kernel." This is +There is nothing stopping others from playing *the kernel*. This is not a security problem: clients must [[trust]] the server from whom they obtain memory objects and also the servers with whom they share the object. Multiple memory managers are a reality that should be diff --git a/microkernel/mach/ipc.mdwn b/microkernel/mach/ipc.mdwn index aaf3ba23..1bb44b59 100644 --- a/microkernel/mach/ipc.mdwn +++ b/microkernel/mach/ipc.mdwn @@ -1,22 +1,21 @@ -[[!meta copyright="Copyright © 2007, 2008 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2007, 2008, 2010 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] -[[General_information|/ipc]] about IPC. +Read about the [[general concept of *inter-process communication* (IPC)|/ipc]]. -An IPC is sent by invoking a [[port]]. <!-- Isn't this wording a bit strange? -``IPC is sent'' --tschwinge --> +On Mach, an IPC is done by invoking a [[port]]. + +The two fundamental operations, to *send* and *receive* [[message]]s, are used +to implement a [[RPC]] system. [[Sequence_numbering]]. [The Unofficial GNU Mach IPC beginner's guide](http://www.nongnu.org/hurdextras/ipc_guide/ipc_guide.html) - -# See Also - -* [[RPC]] diff --git a/microkernel/mach/memory_object.mdwn b/microkernel/mach/memory_object.mdwn new file mode 100644 index 00000000..2342145c --- /dev/null +++ b/microkernel/mach/memory_object.mdwn @@ -0,0 +1,31 @@ +[[!meta copyright="Copyright © 2002, 2003, 2010 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]]."]]"""]] + +Mach's [[virtual_memory]] subsystem uses *memory objects* for supplying the +content of regions of virtual memory in an [[virtual_address_space]]. + +All of these objects are managed by *memory manager*s, that are also called +*pager*s. These can be implemented as user-space processes. + +Both the memory objects, and their managers are kernel objects, and are +accessed by [[port]]s. + +A system's physical memory is conceived as a *memory cache* that contains +*memory cache objects*. So when a [[thread]] accesses a page in its task's +address space, the memory object that includes this page is *cached* in the +memory cache. Memory objects are [[paged out and paged +in|external_pager_mechanism]] by the aforementioned memory managers. The +decision when they should be paged in or paged out is left to [[Mach]]. Each +memory object has an ordered list of memory managers that provide paging. The +last one tried is the *default memory manager* that resides in the microkernel, +in contrast to most of the others. The default memory manager is needed +because the microkernel can't wait infinitely for someone else to free the +memory cache: it just calls the next memory manager hoping it to succeed. diff --git a/microkernel/mach/message.mdwn b/microkernel/mach/message.mdwn new file mode 100644 index 00000000..ba47671e --- /dev/null +++ b/microkernel/mach/message.mdwn @@ -0,0 +1,31 @@ +[[!meta copyright="Copyright © 2002, 2003, 2010 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]]."]]"""]] + +*Messages* are collections of typed data, with a defined layout. + +They are used for [[IPC]], and are sent to and received from [[port]]s. + +These messages are not only opaque data. They can also contain [[port +rights|port]] to be passed to another [[task]]. Port rights are either +*copied* or *moved*. Notice that port receive right must be moved but not +copied because there can't be more than one task that holds the receive right +to a port. The receiving task creates new local port name to the port rights +it received. + +Some data in the message can be *out-of-line data*. In the message, these are +*references* to memory regions ([[memory_object]]s) that are *virtually +copied*. When the message is received in a task, these virtual copies become +part of the task by mapping them into the receiver's [[virtual_address_space]]. +Another key concept that is applied is using *copy-on-write*, which means that +data is not copied immediately, but only when it is changed. This is primarily +used to send large blocks of data efficiently, as it is too expensive to store +them in the kernel address space: extra copied need only be made at the moment +that the memory regions begin to diverge, by threads modifying them. diff --git a/microkernel/mach/mig.mdwn b/microkernel/mach/mig.mdwn index 4275a4b4..331b3bf4 100644 --- a/microkernel/mach/mig.mdwn +++ b/microkernel/mach/mig.mdwn @@ -1,21 +1,34 @@ -[[!meta copyright="Copyright © 2001, 2002, 2003, 2006, 2007, 2008 Free Software -Foundation, Inc."]] +[[!meta copyright="Copyright © 2001, 2002, 2003, 2006, 2007, 2008, 2010 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] -The Mach Interface Generator (MIG) is an [[IDL]] compiler. Based on an -interface definition, it creates stubs to [[invoke]] object methods -and to demultiplex incoming messages. These stubs conveniently hide -the details of Mach's [[IPC]] machinery and make it easy to implement -and use Mach [[interface]]s as [[remote_procedure_calls_(RPC)|rpc]]. +The *Mach Interface Generator* (*MIG*) is an [[IDL]] compiler. Based on an +interface definition, it creates stub code to [[invoke]] object methods and to +demultiplex incoming messages. These stub functions conveniently hide the +details of Mach's [[IPC]] and [[port]] machinery and make it easy to implement +and use Mach [[interface]]s as [[remote procedure calls (RPC)|rpc]]: by using +the stub functions, the client programs can call remote procedures more or less +like any other C function. + +These functions encode arguments into [[message]]s' format (*marshalling*), +wait for a result on a newly created [[reply port|port]], decode return +arguments from the reply message (*demarshalling*, or *unmarshalling*) and pass +them to the client program. Similar actions are provided in the skeletons that +are linked to server programs. + +MIG allows very precise semantics to be specified about what the arguments are +and how to be passed. + + + * [[Documentation]] -* [[Documentation]] # Implementations diff --git a/microkernel/mach/mig/documentation.mdwn b/microkernel/mach/mig/documentation.mdwn index be762960..7d4f1eca 100644 --- a/microkernel/mach/mig/documentation.mdwn +++ b/microkernel/mach/mig/documentation.mdwn @@ -1,13 +1,13 @@ -[[!meta copyright="Copyright © 2002, 2003, 2005, 2007, 2008, 2009 Free Software -Foundation, Inc."]] +[[!meta copyright="Copyright © 2002, 2003, 2005, 2007, 2008, 2009, 2010 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] This is a small collection of links to external documents describing the *Mach Interface Generator* used by GNU Mach. @@ -17,7 +17,7 @@ Interface Generator* used by GNU Mach. A tutorial which demonstrates the use of the C Threads library primitives in writing a multithreaded program and the use of the Mach Interface Generator -(MIG) to generate remote procedure calls for interprocess communication. Like +(MIG) to generate remote procedure calls for inter-process communication. Like its companion tutorial, it is based on the Mach 2.5 system. However, the concepts are applicable to Mach 3.0 user level programming. @@ -41,9 +41,9 @@ Slides to Rich Drave's talk on MIG, on November 21, 1991: Mig is an implementation of a subset of the Matchmaker **language**. "Matchmaker is a language for specifying and automating the generation of -multilingual interprocess communication interfaces. MIG is an interim +multilingual inter-process communication interfaces. MIG is an interim implementation of a subset of the Matchmaker language that generates C and C++ -remote procedure call interfaces for interprocess communication between Mach +remote procedure call interfaces for inter-process communication between Mach tasks." Richard P. Draves, Michael B. Jones, Mary R. Thompson, *MIG - THE MACH diff --git a/microkernel/mach/mig/gnu_mig.mdwn b/microkernel/mach/mig/gnu_mig.mdwn index 1bcbd545..0de1bd67 100644 --- a/microkernel/mach/mig/gnu_mig.mdwn +++ b/microkernel/mach/mig/gnu_mig.mdwn @@ -1,13 +1,13 @@ -[[!meta copyright="Copyright © 2001, 2006, 2008, 2009 Free Software Foundation, -Inc."]] +[[!meta copyright="Copyright © 2001, 2006, 2008, 2009, 2010 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] GNU MIG is the GNU distribution of the [[Mach_3.0_interface_generator_*MIG*|mig]], as maintained by the GNU Hurd @@ -20,5 +20,9 @@ software in the GNU system that uses Mach-based GNU MIG is fully compatible with [[OSF_MIG|mig]]. +Like its predecessor, it can only generate C code, that has to be compiled and +linked to client and server programs respectively ([[!taglink +open_issue_mig]]). + * [[Building]] - building (and obtaining) GNU MIG * [[Open Issues|tag/open_issue_mig]] diff --git a/microkernel/mach/port.mdwn b/microkernel/mach/port.mdwn index af4a0c8d..ba2e22c2 100644 --- a/microkernel/mach/port.mdwn +++ b/microkernel/mach/port.mdwn @@ -1,41 +1,85 @@ -[[!meta copyright="Copyright © 2007, 2008 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2002, 2003, 2007, 2008, 2010 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]]."]]"""]] - -Mach ports are [[capabilities|capability]]. - -A Mach port is a kernel queue. Each port has associated with -it a receive right and one or more send and send-once rights. -A queue can hold a number of messages. Once the queue is full, -the send blocks until their is space to enqueue the message -(this is interruptible via a timeout mechanism). - -A receive right designates a queue and authorizes the holder to -dequeue messages from the queue, and to create send and send-once -rights. - -Send and send-once rights designate a queue and authorize the -hold to enqueue messages (in the case of a send-once right, -a single message). Enqueuing a message is equivalent to -[[invoke|invoking]] a capability. - -Send and receive rights are named using local names. Each -task has associated with it a port [[address_space]]. A ports -are addressed via this table. Each task thus has its own -private [[naming_context]] for ports. - -Ports can be [[delegate]]d in an [[IPC]] message. When the -receiver dequeues the message, the right is made available -to it. - -A [[thread]] can only block receiving on a single port. To work -around this, the concept of a port set was introduced. A receive -right can be added to (at most) one port set. When a thread -receives from a port set, it dequeues from any of the ports that -has a message available. +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[Mach]] *port*s are [[capabilities|capability]], and are also essentially +similar to [[UNIX]] pipes. They are communication channels, implemented by +kernel queues. + +Each port has associated with it one *receive right* and one or more *send +right*s and *send-once right*s. That is, there is one receiver and one or more +senders -- a unidirectional communication channel. Only with the corresponding +port right, access to a port is possible; this is enforced by Mach. + +The kernel queue can hold a number of [[message]]s. Once the queue is full, +the send blocks until there is space to enqueue the message (this is +interruptible via a timeout mechanism). + +A receive right [[designates|designation]] a queue and authorizes the holder to +dequeue messages from the queue, and to create send and send-once rights. + +Send and send-once rights designate a queue and authorize the hold to enqueue +messages (in the case of a send-once right, a single message). Enqueuing a +message is equivalent to [[invoke|invoking]] a capability. + +Ports are automatically destroyed when there is no associated port right to +them. + +Mach knows what port rights belong to each task, but [[thread]]s that running +in the context of a task refer to ports by means of send and receive rights +that are named using local *port names*. These port names are plain integers, +like [[UNIX file descriptors|unix/file_descriptor]]. Only these local names +can be used by [[thread]]s for invoking operations on ports, threads do not +deal with port rights directly. + +For that, each task has associated with it a *port address_space*, or *port +name space*. All ports are addressed via this table. Each task thus has its +own private [[naming_context]] for port rights. + +So, the picture is that after obtaining a port send right, the client uses a +port name to send [[message]]s to the port, or exactly one message if it's a +send-once right. These messages are (probably) queued and when the server task +tries to receive messages by having a [[thread]] use its port receive right, it +gets the message(s). This is called [[IPC]]. + +Port rights themselvse can be [[delegate]]d in a [[message]], too. When the +receiver dequeues the message, the right is made available to it. + +The delivery of [[message]]s is reliable and strictly ordered. When a +[[thread]] sends messages *1* and *2*, it is guaranteed that the receiving +[[task]] will catch them in the same order. Of course, there can be +intermediate messages that are sent by other threads. + +Ports are objects that are implemented by the [[kernel]], and they are +kernel-protected resources. There is no way for a [[task]] to do anything with +a port unless it have corresponding port right. + +Due to this, ports are globally unique. This makes them ideal for constituting +system-wide *object references*. For example, the [[RPC]] system as used by +the GNU Hurd works by invoking *methods* on such object references. The +available methods are defined in [[hurd/interface]] files, and are processes by +the [[MIG]] tool. + +Invoking an operation on a port does not transfer the current execution control +to the receiver, but instead is an asynchronous operation. For this, and +especially in a [[RPC]] system, the sender may include a *reply port* using a +send-once right, and synchronize (block) on that one. + +A [[thread]] can only block receiving on a single port. To work around this, +the concept of a *port set* was introduced. A receive right can be added to +(at most) one port set. These port sets look like port receive rights, but +cannot be passed to other tasks, and there are additional operations for adding +and removing port receive rights. + +When a server process' thread receives from a port set, it dequeues exactly one +message from any of the ports that has a message available in its queue. + +This concept of port sets is also the facility that makes convenient +implementation of [[UNIX]]'s `select` [[system_call]] possible. diff --git a/microkernel/mach/rpc.mdwn b/microkernel/mach/rpc.mdwn index 72acfaa0..60275a86 100644 --- a/microkernel/mach/rpc.mdwn +++ b/microkernel/mach/rpc.mdwn @@ -1,15 +1,21 @@ -[[!meta copyright="Copyright © 2007, 2008 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2002, 2003, 2007, 2008, 2010 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]]."]]"""]] +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] -[[General_information|/rpc]] about RPC. +Read about the [[general concept of a *remote procedure call* (RPC)|/rpc]]. Uses Mach's [[IPC]] [[mechanism]]. -Stub code generated by [[MIG]]. +The [[port]] abstraction allows RPCs to be executed on another computer +transparently. This can be implemented with user [[task]]s, but there is an +implementation in the kernel possible, too, which is called *NORMA*, but is not +avilable in [[GNU Mach|gnumach]]. + +The RPC stub code generated by [[MIG]]. diff --git a/microkernel/mach/task.mdwn b/microkernel/mach/task.mdwn new file mode 100644 index 00000000..c03c6a14 --- /dev/null +++ b/microkernel/mach/task.mdwn @@ -0,0 +1,23 @@ +[[!meta copyright="Copyright © 2002, 2003, 2010 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]]."]]"""]] + +A Mach *task* is a collection of resources, a [[virtual_address_space]], and a +[[port name space|port]]. They depend on [[thread]]s for executing program +code: a task alone has no means to do so. + +Switching from one task to another one involves doing a *context switch*, which +is usually not a cheap operation, as it involves switching the hardware's idea +of the memory layout ([[virtual_address_space]]), amongst others. + +Mach tasks are distinct from [[UNIX processes|unix/process]] in that they +provide less facilities. In processes, there are [[unix/signal]]s, process / +group / session IDs, [[unix/file_descriptor]]s and many other things. Tasks +are used for resource allocation and sharing; they are *resource container*s. diff --git a/microkernel/mach/thread.mdwn b/microkernel/mach/thread.mdwn new file mode 100644 index 00000000..e27bb117 --- /dev/null +++ b/microkernel/mach/thread.mdwn @@ -0,0 +1,37 @@ +[[!meta copyright="Copyright © 2002, 2003, 2010 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]]."]]"""]] + +A Mach *thread* belongs to exactly one [[task]], and is the means of execution. +The task supplies the resources. + +Mach threads are implemented inside the [[kernel]], as opposed to other +systems' user-level thread packages. + +A thread (theoretically) runs concurrently with all the other threads of a +system. If the system provides several processors, they can be used for +simultaneously running either several threads of the same task, or several +threads of different tasks. <!-- This is called SMP; the processors use +*shared memory*. --> [[!tag open_issue_documentation]] <!-- This needs a new +page, also covering Mach's `processor_set`s, and non-SMP, but still +multiprocessor systems. --> (But this is currently not support in [[GNU +Mach|gnumach]].) + +It is easy for the kernel to switch execution from one thread to another one +inside the same task: essentially, it only involves exchanging a few processor +registers' state. + +Threads have scheduling parameters and maintain various statistics about +themselves. + +On GNU/Hurd, APIs for Mach threads and thereabouts are provided by the +[[hurd/libthreads]] (cthreads), and [[libpthread]] (POSIX Threads) packages. + +A task backing a thread is the basis for a [[UNIX process|unix/process]]. diff --git a/microkernel/mach/virtual_address_space.mdwn b/microkernel/mach/virtual_address_space.mdwn new file mode 100644 index 00000000..97bc5f6b --- /dev/null +++ b/microkernel/mach/virtual_address_space.mdwn @@ -0,0 +1,36 @@ +[[!meta copyright="Copyright © 2002, 2003, 2010 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]]."]]"""]] + +*Virtual address space*s in Mach define the valid virtual addresses that can be +used by [[thread]]s under execution in the [[task]] that owns that address +space. Each task has only one address space and each address space belongs to +only one task. So when we want to name an address space (for example, in the +Mach API) we name it by the task it belongs to. + +These address spaces are divided into *pages*. Each page has individual +properties like *access rights* (*read* / *write* / *execute*), *inheritance +attributes* (*no inheritance* / *copy* / *share*) and some other system +properties. Page manipulation is optimized to help moving large blocks of data +from one address space to another, for example when one thread provides data to +another thread -- *client / server* technology. + +Memory ranges of pages that can be controlled as a whole are called +*[[memory_object]]*s. + +*Wired pages* are those that cannot be [[paged out|external_pager_mechanism]]. +For example, Mach itself is a task with its own address space and threads, and +all of its pages are wired. + +*Precious pages* are those that must not be discarded silently when they are +clean and memory is needed. For example, a memory manager that shares memory +across a network could not restore a page if it is silently discarded because +it is unmodified. This is not valid for the well-known [[pager +managers|external_pager_mechanism]] that use disks as backing store. |