The pthread_barrier_wait() function shall synchronize participating
threads at the barrier referenced by barrier. The calling thread shall
block until the required number of threads have called
pthread_barrier_wait() specifying the barrier.
When the required number of threads have called pthread_barrier_wait()
specifying the barrier, the constant PTHREAD_BARRIER_SERIAL_THREAD shall be
returned to one unspecified thread and zero shall be returned to each of the
remaining threads. At this point, the barrier shall be reset to the state it
had as a result of the most recent pthread_barrier_init() function that
The constant PTHREAD_BARRIER_SERIAL_THREAD is defined in
<pthread.h> and its value shall be distinct from any other value
returned by pthread_barrier_wait().
The results are undefined if this function is called with an uninitialized
If a signal is delivered to a thread blocked on a barrier, upon return from the
signal handler the thread shall resume waiting at the barrier if the barrier
wait has not completed (that is, if the required number of threads have not
arrived at the barrier during the execution of the signal handler); otherwise,
the thread shall continue as normal from the completed barrier wait. Until the
thread in the signal handler returns from it, it is unspecified whether other
threads may proceed past the barrier once they have all reached it.
A thread that has blocked on a barrier shall not prevent any unblocked thread
that is eligible to use the same processing resources from eventually making
forward progress in its execution. Eligibility for processing resources shall
be determined by the scheduling policy.
Upon successful completion, the pthread_barrier_wait() function shall
return PTHREAD_BARRIER_SERIAL_THREAD for a single (arbitrary) thread
synchronized at the barrier and zero for each of the other threads. Otherwise,
an error number shall be returned to indicate the error.
Applications using this function may be subject to priority inversion, as
discussed in the Base Definitions volume of
IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.
The pthread_barrier_wait() function is part of the Barriers option and
need not be provided on all implementations.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html