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Diffstat (limited to 'microkernel/mach/port.mdwn')
| -rw-r--r-- | microkernel/mach/port.mdwn | 24 |
1 files changed, 14 insertions, 10 deletions
diff --git a/microkernel/mach/port.mdwn b/microkernel/mach/port.mdwn index 7f02628d..26b55456 100644 --- a/microkernel/mach/port.mdwn +++ b/microkernel/mach/port.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2002, 2003, 2007, 2008, 2010 Free Software +[[!meta copyright="Copyright © 2002, 2003, 2007, 2008, 2010, 2011 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable @@ -10,8 +10,8 @@ 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. +similar to [[UNIX]] pipes. They are unforgeable 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 @@ -39,7 +39,7 @@ 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 +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. @@ -58,20 +58,24 @@ The delivery of [[message]]s is reliable and strictly ordered. When a 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. +kernel-protected resources: they are unforgeable, and 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. +system-wide *object references*. (Fruther reading: +{{$capability#wikipedia_object-capability_model}}.) 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. + +# Port Set + 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 |