Interpretations

Answering questions that may arise related to the meaning of portions of an IEEE standard concerning specific applications.

IEEE Standards Interpretations for IEEE Std 1003.1™-2001 IEEE Standard for Information Technology - Portable Operating System Interface (POSIX®)

Copyright © 2006 by the Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue New York, New York 10016-5997 USA All Rights Reserved.

Interpretations are issued to explain and clarify the intent of a standard and do not constitute an alteration to the original standard. In addition, interpretations are not intended to supply consulting information. Permission is hereby granted to download and print one copy of this document. Individuals seeking permission to reproduce and/or distribute this document in its entirety or portions of this document must contact the IEEE Standards Department for the appropriate license. Use of the information contained in this document is at your own risk.

IEEE Standards Department Copyrights and Permissions 445 Hoes Lane, Piscataway, New Jersey 08855-1331, USA

Interpretation Request #28
Topic: pthread_cond_wait deadlock situations Relevant Sections: XSH pthread_cond_wait

It is unclear what the expected behavior is in case of a recursive-type mutex which would be locked several times. In this case, there could be several interpretations: -> The internal counter of the mutex is decreased once, as if pthread_mutex_unlock had been called. In this case, the mutex is not released as requested line 33271. -> The internal counter of the mutex is decreased to zero, as if pthread_mutex_unlock had been called enougth times to release the mutex. -> It is illegal to call this function with a recursive mutex locked more than once.

According to which is the correct behavior (see below), here are the actions to take: -> line 33271 should be like: "These function atomically release mutex (the effects being the same as if pthread_mutex_unlock had been called) and cause..." -> In this case a new paragraph should be inserted after the line 33276: "In case of a mutex of type PTHREAD_MUTEX_RECURSIVE, if the mutex has been locked more than once by the calling thread, the mutex is released as if pthread_mutex_unlock was called enought times. When the thread will leave the pthread_cond_wait or pthread_cond_timedwait function, the mutex shall be re-acquired as if pthread_mutex_lock was called the same number of times as pthread_mutex_unlock was called." -> this should be added after line 33270: "In case of a mutex of type PTHREAD_MUTEX_RECURSIVE, if the mutex is locked several times, the function shall return an error."

Interpretation Response
The standard does not speak to this issue, and as such no conformance distinction can be made between alternative implementations based on this. This permits implementations to choose how to handle situations where an application might deadlock, some implementations might choose to detect and report that deadlock while others wouldn't.

Rationale for Interpretation
None.