IEEE Standards Interpretations for IEEE Std 1003.1c™-1995 IEEE Standard for Information Technology--Portable Operating System Interface (POSIX(R)) - System Application Program Interface (API) Amendment 2: Threads Extension (C Language)
Copyright © 1996 by the Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue New York, New York 10016-5997 USA All Rights Reserved.
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Interpretation Request #44
Topic: Threads Options Relevant Clauses: 220.127.116.11, 2.9.3
The POSIX spec lists in 18.104.22.168, page 4, the symbolic constants that define the implementation options required by conforming implementations. Only these four symbols are listed for threads: _POSIX_THREADS Threads option (in 2.9.3) _POSIX_THREAD_SAFE_FUNCTIONS Thread-Safe Functions option (in 2.9.3) _POSIX_THREAD_PRIO_INHERIT Priority inheritance option (in 2.9.3) _POSIX_THREAD_PRIORITY_SCHEDULING Thread Execution Scheduling option (in 2.9.3) It says that the remaining constants defined in 2.9.3 and 2.9.4 are useful for testing but are not required by a conforming implementation. Functions which are not implemented must be callable with the defined syntax, but can do nothing except return an error.
The following symbolic constants are not listed in 22.214.171.124 or 2.9.3 as required, but are included in the list of options in table 2.10, page 54. _POSIX_THREAD_ATTR_STACKADDR: thread stack address attribute functions _POSIX_THREAD_ATTR_STACKSIZE: thread stack size attribute functions _POSIX_THREAD_PRIO_PROTECT: thread priority protection functions _POSIX_THREAD_PROCESS_SHARED: process shared synchronization functions I interpret this to mean we can exclude implementing the 12 functions below (providing only a stub that returns the error ENOSYS) and still have a conforming implementation. _POSIX_THREAD_ATTR_STACKADDR pthread_attr_getstackaddr() pthread_attr_setstackaddr() _POSIX_THREAD_ATTR_STACKSIZE pthread_attr_getstacksize() pthread_attr_setstacksize() _POSIX_THREAD_PRIO_PROTECT pthread_mutexattr_setprioceiling() pthread_mutexattr_getprioceiling() pthread_mutex_getprioceiling() pthread_mutex_setprioceiling() _POSIX_THREAD_PROCESS_SHARED pthread_mutexattr_getpshared() pthread_mutexattr_setpshared() pthread_condattr_getpshared() pthread_condattr_setpshared() One point of confusion is the functions in the _POSIX_THREAD_PRIORITY_SCHEDULING option.
Subclause 126.96.36.199 indicates these are required for a conforming implementation; however, each of the functions is allowed to return the error ENOSYS if they are not implemented (Clause 13.5). All other functions which I've interpreted as being required cannot return this error. We would like to know the minimum set of options which are required for a POSIX Threads implementation to be conforming.
The interpretation request asks two questions. Responses are given for each. 1) (first line) What is the minimum functionality required to be conforming to IEEE 1003.1 1996: The standard is clear on page 3 lines 67 to 81 that a 9945-1 1996 conforming implementation shall support all the non-optional interfaces. 2) (second from last line) What is the minimum set of options which are required for POSIX Threads implementation to be conforming. The standard is clear in defining a set of options in the area of multithreading for implementations to possibly support. It does not define the notion of a 9945-1 1996 'threads' conforming implementation other than as the implementation choses to support one or more of the thread option as required by conforming applications. Application Environment Profiles (AEPs) are the vehicle for defining further conformance sets required for specific applications.
Rationale for Interpretation