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. 345 East 47th Street New York, New York 10017 USA All Rights Reserved.
These are interpretations of IEEE Std 1003.1c-1995.
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Interpretation Request #8
Topic: pthread_key_create() Relevant Clauses: 220.127.116.11
There seems to be an editorial error in IEEE Std 1003.1c-1995 regarding pthread_key_create() The pthread_key_create section, 18.104.22.168 of IEEE Std 1003.1c-1995, is very unclear. As written today it easily leads one to believe that it is required that the destructor function be called until the thread-specific value becomes NULL, or until PTHREAD_DESTRUCTOR_ITERATIONS iterations have occured, whichever comes first. If you read the draft POSIX 1003.1c standard revisions, it's clear what the intent was. Between draft standards a sentence was lost which said "Before each destructor is called, the thread's value for the corresponding key is set to NULL". The re-iteration exists so that if the destructor uses keys, they will be destroyed in a re-call to the destructor. Was this omission an editorial error?
The standard states that the destructor is called with the current associated value as its only argument and it is repeatedly called until PTHREAD_DESTRUCTOR_ITERATIONS or the value associated with the key becomes null. Conforming implementations must conform to this. However, concerns have been raised that the intent of the working and balloting groups was somewhat different and that the associated value should automatically set to NULL before the destructor is called in order to prevent infinite loops. This is needed since the destructor function does not have a way to determine which key that caused it to be invoked and thus does not have a way to null the value. The committee feels that this is a problem and it is being referred to the sponsor for consideration.
Rationale for Interpretation