pse51.txt

rtai-3.1-test3的源代码(Real-Time Application Interface )

Overview
========

The PSE51 emulation module on top of Xenomai aims at providing an (almost) POSIX
compatible API. In order to help porting applications from other PSE51
compatible APIS (like RTLinux) it will contain some non portable extensions to
the POSIX specification.

This layer already contains most basic features :
- threads,
- mutexes,
- semaphores,
- condition variables,
- basic support for old-fashioned signals (not realtime ones),
- cancellation, cancellation handlers
- thread specific data.



Known variations from the POSIX specification.
===============================================

Using the Xenomai PSE51 skin, you may observe some variations from the
interfaces and behaviours described in the POSIX specification. Here are the 
known ones :

- the skin header file does not define the _POSIX* compile-time constants ;
 
- nor does it defines the objects static initializers
  (PTHREAD_MUTEX_INITIALIZER, etc...) except for pthread_once_t ;

- manually setting the thread stack address in thread attributes is not
  supported ;

- thread attributes contain two non portable extensions : pthread_attr_set/getfp
  to control whether the thread to be created will use the FPU,
  pthread_attr_set/getname to choose the name of threads ;

- priority ceiling protocol is not supported, use priority inheritance instead ;

- reusing the same pointer as the parameter to several functions *_init should
  always return EBUSY instead of overwriting some memory area.

- simultaneous calls to pthread_join() specifying the same target thread simply
  locks all the callers until the target thread exits, is canceled or killed.

- thanks to xenomai kernel mutexes, most functions should be asynchronous signal
  safe.


Undefined behaviour.
=====================

Some special cases are not covered by the POSIX specification or described as
being "undefined", but some implementation decisions had to be made :

- trying to post a semaphore whose count is already SEM_VALUE_MAX returns
  EINVAL ;

- pthread_equal simply compares the two pthread_t, which are pointers, no
  attempts is made to verify whether the corresponding threads exist.



TODO List
==========

The PSE51 skin is still a work in progress, it lacks some features which will be 
added gradually :
- RTLinux non portable extensions ;
- CLOCK_REALTIME support (the only clock supported is CLOCK_MONOTONIC for now,
  which does not make any difference as long as clock_gettime does not get 
  called);
- rwlocks/barriers/message queues ;
- realtime signals ;
- timers.



Module parameters
=================

The following parameters can be passed at startup to the PSE51
API emulation module:

- "tick_hz_arg", clock tick period. Defaults to 100 Hz.