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 #110
Topic:
raise vs asynchronous signal Relevant Sections: 2.2.2.10 , p14 l 120 PASC

Is the result of raise () (or kill() of self) a synchronous or asynchronous signal?

This is to bring work in scope for the Austin Group revision. The problem is that synchronous and asynchronous signals are not quite well defined, particularly in the case of raise(). The current wording is "a signal that is not attributable to a specific thread". Since all signals are generated by SOME thread, they are all attributable to a specific thread (just not neccessarily the one handling the signal). I believe the thrust of it is "attributable to the thread handling the signal". Right now, "synchronously generated signal" is being treated as a synonym for "execution fault signal", which it isn't, at least according to the definition of the word "synchronously", because raise() would also be synchronously generated. Suggested alternative wording: Asynchronously generated signal: "A signal that is not attributable to the actions of the thread handling the signal." and Synchronously generated signal: "A signal that is attributable to the thread which is handling it, and which is handled immediately upon its generation; that is, is not blocked or ignored. Note: timer and I/O completion signals are considered attributable to the timer or I/O system." Note... there are two intertwined issues here; please address both of them: 1) "attributable to a process" is trivially true; it's "the same thread" that's critical to fixing this. 2) "handled immediately". This certainly is the intent, but it could be circumvented. Doing a raise() of a signal known to be blocked is not an unreasonable programming technique, but it wouldn't be a synchronous signal. On the other hand, doing a raise() of an unblocked signal is synchronous with the program. (Or... rename the concept to "error signal" or something like that.) --

Interpretation Response
The answer to the question in the problem statement is "synchronous". The problem raised in the "solution" section is being referred to the sponsor.

Rationale for Interpretation
New definitions are required, those proposed will not work, this is referred to the sponsor. Forwarded to Interpretations group: 19 June 2000 Proposed resolution: 25 July 2000 Finalized Interpretation: 29 August 2000