PTHREAD_BARRIER(3)

NAME
pthread_barrier_destroy, pthread_barrier_init, pthread_barrier_wait - destroy, initialize or wait on a barrier object

LIBRARY
libpthread

SYNOPSIS
#include <pthread.h>
int
pthread_barrier_destroy(pthread_barrier_t *barrier);
int
pthread_barrier_init(pthread_barrier_t *barrier, const pthread_barrierattr_t *attr, unsigned count);
int
pthread_barrier_wait(pthread_barrier_t *barrier);

DESCRIPTION
The pthread_barrier_init() function will initialize barrier with attributes specified in attr, or if it is NULL, with default attributes. The number of threads that must call pthread_barrier_wait() before any of the waiting threads can be released is specified by count. The pthread_barrier_destroy() function will destroy barrier and release any resources that may have been allocated on its behalf.

The pthread_barrier_wait() function will synchronize calling threads at barrier. The threads will be blocked from making further progress until a sufficient number of threads calls this function. The number of threads that must call it before any of them will be released is determined by the count argument to pthread_barrier_init(). Once the threads have been released the barrier will be reset.

IMPLEMENTATION NOTES
In both libkse and libthr the PTHREAD_BARRIER_SERIAL_THREAD return value will always be returned by the last thread to reach the barrier.

RETURN VALUES
If successful, both pthread_barrier_destroy() and pthread_barrier_init() will return zero. Otherwise, an error number will be returned to indicate the error. If the call to pthread_barrier_wait() is successful, all but one of the threads will return zero. That one thread will return PTHREAD_BARRIER_SERIAL_THREAD. Otherwise, an error number will be returned to indicate the error.

None of these functions will return EINTR.

ERRORS
The pthread_barrier_destroy() function will fail if:

[EBUSY]
    An attempt was made to destroy barrier while it was in use.

The pthread_barrier_destroy() and pthread_barrier_wait() functions may fail if:

[EINVAL]
    The value specified by barrier is invalid.

The pthread_barrier_init() function will fail if:

[EAGAIN]
    The system lacks resources, other than memory, to initialize barrier.

[EINVAL]
    The count argument is less than 1.

[ENOMEM]
    Insufficient memory to initialize barrier.

SEE ALSO
pthread_barrierattr(3)

HISTORY
The pthread_barrier_destroy(), pthread_barrier_init() and pthread_barrier_wait() functions first appeared in libkse in FreeBSD 5.2, and in libthr in FreeBSD 5.3.