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PTHREAD_ONCE(3) BSD Library Functions Manual PTHREAD_ONCE(3)
pthread_once -- dynamic package initialization
POSIX Threads Library (libpthread, -lpthread)
pthread_once(pthread_once_t *once_control, void (*init_routine)(void));
pthread_once_t once_control = PTHREAD_ONCE_INIT;
The first call to pthread_once() by any thread in a process, with a given once_control, will
call the init_routine() with no arguments. Subsequent calls to pthread_once() with the same
once_control will not call the init_routine(). On return from pthread_once(), it is guaran-
teed that init_routine() has completed. The once_control parameter is used to determine
whether the associated initialization routine has been called.
The function pthread_once() is not a cancellation point. However, if init_routine() is a
cancellation point and is cancelled, the effect on once_control is as if pthread_once() was
The constant PTHREAD_ONCE_INIT initializes the static once synchronization control structure
once_control to be used with pthread_once(). The behavior of pthread_once() is undefined if
once_control has automatic storage duration or is not initialized by PTHREAD_ONCE_INIT.
If successful, the pthread_once() function will return zero. Otherwise an error number
will be returned to indicate the error.
The function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
BSD July 9, 2010 BSD
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