PTHREAD_BARRIER_WAIT(3C) Standard C Library Functions

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)