Thread: sig_atomic_t to avoid mutex/critical sections?

  1. #1
    Alessio Stella
    Join Date
    May 2008
    Italy, Bologna

    Question sig_atomic_t to avoid mutex/critical sections?

    If I use a sig_atomic_t x; data and with Linux pthreads I let them do only this:

    (2) or (separately)
    if (x==value) {do something (not with x)}
    (3) or (separately)
    other variable (not shared) = x;
    Can I be sure there is no race condition/unpredicted event/problem even if I do not use pthread_mutex_lock()/trylock()/unlock() to protect the shared sig_atomic_t x data?

    In a few words: is it correct to speed up a software using sig_atomic_t data instead of mutexed data to prevent malfunctioning on shared data with the fundamental condition that data are as little as 2-4 bytes and are accessed only in the very simple way above?

  2. #2
    Registered User Codeplug's Avatar
    Join Date
    Mar 2003
    sig_atomic_t doesn't really have anything to do with multi-threaded programming. The C standard says that any access to a global within a signal handler must be a write access and the type must be "volatile sig_atomic_t". The standard doesn't say much else on the subject.

    As for POSIX, it's fairly clear on memory synchronization requirements in section 4.10:

    The only way you can be sure of anything is to follow POSIX memory synchronization requirements.


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