PTHREAD_BARRIER_WAIT(3C) Standard C Library Functions PTHREAD_BARRIER_WAIT(3C)

NAME

pthread_barrier_wait - synchronize at a barrier

SYNOPSIS

cc -mt [ flag... ] file... [ library... ]
#include <pthread.h>

int pthread_barrier_wait(pthread_barrier_t *barrier);

DESCRIPTION

The pthread_barrier_wait() function synchronizes participating threads at
the barrier referenced by barrier. The calling thread blocks 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 is
returned to one unspecified thread and 0 is returned to each of the
remaining threads. At this point, the barrier is reset to the state it
had as a result of the most recent pthread_barrier_init(3C) function that
referenced it.


The constant PTHREAD_BARRIER_SERIAL_THREAD is defined in <pthread.h> and
its value is 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 resumes 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 continues 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 does 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 is determined by the scheduling
policy.

RETURN VALUES

Upon successful completion, the pthread_barrier_wait() function returns
PTHREAD_BARRIER_SERIAL_THREAD for a single (arbitrary) thread
synchronized at the barrier and 0 for each of the other threads.
Otherwise, an error number is returned to indicate the error.

ERRORS

The pthread_barrier_wait() function will fail if:

EINVAL
The value specified by barrier does not refer to an initialized
barrier object.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

pthread_barrier_destroy(3C), attributes(7), standards(7)


January 30, 2004 PTHREAD_BARRIER_WAIT(3C)