IEEE Standards Interpretations for IEEE Std 1003.1b™-1993 IEEE Standard for Information Technology - Portable Operating System Interfaces (POSIX(R)) - Part 1: System Application Program Interface (API) - Amendment 1: Realtime Extension [C language]
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Interpretation Request #6
Topic: semaphores Relevant Sections: 188.8.131.52, page 222, lines 110-118
What are the meanings of read and write permissions with respect to semaphores? Is there a method of opening an existing semaphore for O_RDONLY or O_RDWR or O_WRONLY? What is the effect of calling sem_wait, sem_trywait or sem_post on a semaphore which was created with read-only permission? Write-only permission? The standard does not specify a behavior if the semaphore was not created with both read and write permissions. Should the post and wait operations require both read/write access since this is both a read and write operation? There is no error return for this situation.
The standard is clear: only the the O_CREAT and O_EXCL flags have a defined interpretation. The other flags are unspecified and a strictly conforming application will not use them. Any usage or interpretations of the flags by an implementation would be an extension.
Rationale for Interpretation