PTHREAD_BARRIER_WAIT(P) POSIX Programmer's Manual PTHREAD_BARRIER_WAIT(P)
pthread_barrier_wait - synchronize at a barrier (ADVANCED REALTIME THREADS)
int pthread_barrier_wait(pthread_barrier_t *barrier);
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 bar-
rier, 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_bar-
rier_init() function that referenced it.
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 barrier.
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 com-
pleted (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
A thread that has blocked on a barrier shall not prevent any unblocked thread that is eli-
gible to use the same processing resources from eventually making forward progress in its
execution. Eligibility for processing resources shall be determined by the scheduling
Upon successful completion, the pthread_barrier_wait() function shall return PTHREAD_BAR-
RIER_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 pthread_barrier_wait() function may fail if:
EINVAL The value specified by barrier does not refer to an initialized barrier object.
This function shall not return an error code of [EINTR].
The following sections are informative.
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 pro-
vided on all implementations.
pthread_barrier_destroy() , the Base Definitions volume of IEEE Std 1003.1-2001,
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_BARRIER_WAIT(P)