Interpretations

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

IEEE Standards Interpretation for IEEE Std 1003.1™-1990 IEEE Standard for Information Technology--Portable Operating System Interfaces (POSIX®)

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Interpretation Request #119
Topic:
sigtimedwait and EAGAIN error Relevant Sections: page 90, clause 3.3.84, ll 1295-1296 PASC

Austin Group XSHd1 ERN 345 stated the following problem (to be clear these are the words of the originator of the ERN): ETIMEDOUT is used for pthread_cond_timedwait() in exactly the same context. Normally EAGAIN is reserved for use when some resource limit temporarily causes failure of an API, while ETIMEDOUT is specified for a user-specified timeout. Also, all of the realtime amendments in progress use ETIMEDOUT for this. I believe there is either an interp request or an unresolved objection against .1a calling for this to be made consistent. Action: Consider changing this to ETIMEDOUT unless the potential for breakage is too great.

The standard is clear in its requirement for EAGAIN. The issue is whether the standard has a defect. In hindsight ETIMEDOUT would seem a more appropriate error, however would that break applications?

Interpretation Response
The standard clearly states the requirements ,and conforming implementations must conform to this. To change this would break backwards compatibility. No change is required.

Rationale for Interpretation
There is very little reason one would use sigtimedwait() without intending to check for timeout, so we would expect most users of this interface to be broken by the proposed change. Whilst consistency is desirable, there appears to be no way to make a change without breaking source compatibility. Forwarded to Interpretations group: 29 Nov 2000 Proposed resolution: 15 Feb 2001 Finalized: 15 Mar 2001