NAME
pthread_barrier —
barrier
interface
LIBRARY
POSIX Threads Library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h>
int
pthread_barrier_init(
pthread_barrier_t
* restrict barrier,
const
pthread_barrierattr_t * restrict attr,
unsigned int count);
int
pthread_barrier_destroy(
pthread_barrier_t
*barrier);
int
pthread_barrier_wait(
pthread_barrier_t
*barrier);
int
pthread_barrierattr_getpshared(
const
pthread_barrierattr_t * __restrict attr,
int * __restrict pshared);
int
pthread_barrierattr_setpshared(
pthread_barrierattr_t
* attr,
int pshared);
DESCRIPTION
The
pthread_barrier_init() function creates a new barrier with
attributes
attr and
count. The
count parameter indicates the number of threads which
will participate in the barrier. The
pthread_barrierattr_init(3)
function may be used to specify the attributes supplied in
attr. If
attr is
NULL
, the default attributes are used. Barriers are
most commonly used in the decomposition of parallel loops.
The
pthread_barrier_destroy() function causes the resources
allocated to
barrier to be released. No threads should
be blocked on
barrier.
The
pthread_barrier_wait() function causes the current thread
to wait on the barrier specified. Once as many threads as specified by the
count parameter to the corresponding
pthread_barrier_init() call have called
pthread_barrier_wait(), all threads will wake up, return
from their respective
pthread_barrier_wait() calls and
continue execution.
The
pthread_barrierattr_getpshared() function shall obtain the
value of the process-shared attribute from the attributes object referenced by
attr. The
pthread_barrierattr_setpshared() function shall
set the process-shared attribute in an initialized attributes object
referenced by attr.
RETURN VALUES
If successful,
pthread_barrier_init() will return zero and put
the new barrier id into
barrier, otherwise an error
number will be returned to indicate the error.
If successful,
pthread_barrier_destroy() will return zero.
Otherwise an error value will be returned.
If successful,
pthread_barrier_wait() will return zero for all
waiting threads except for one. One thread will receive status
PTHREAD_BARRIER_SERIAL_THREAD
, which is intended to
indicate that this thread may be used to update shared data. It is the
responsibility of this thread to insure the visibility and atomicity of any
updates to shared data with respect to the other threads participating in the
barrier. In the case of failure, an error value will be returned.
If successful,
pthread_barrierattr_getpshared() shall return
zero and store the value of the process-shared attribute of attr into the
object referenced by the
pshared parameter. Otherwise,
an error number shall be returned to indicate the error.
If successful,
pthread_barrierattr_setpshared() shall return
zero; Otherwise, an error number shall be returned to indicate the error.
ERRORS
The
pthread_barrier_init() function may fail if:
-
-
- [
EINVAL
]
- The value specified by count is zero
or attr is invalid.
The
pthread_barrier_destroy() function may fail if:
-
-
- [
EBUSY
]
- The barrier still has active threads
associated with it.
-
-
- [
EINVAL
]
- The value specified by barrier is
invalid.
The
pthread_barrier_wait() function may fail if:
-
-
- [
EINVAL
]
- The value specified by barrier is
invalid.
The
pthread_barrierattr_setpshared() function and the
pthread_barrierattr_getpshared() function may fail if:
-
-
- [
EINVAL
]
- The value specified by attr is
invalid.
SEE ALSO
pthread_barrierattr(3),
pthread_cond(3),
pthread_mutex(3)
STANDARDS
These functions conform to
IEEE Std 1003.1-2001
(“POSIX.1”).
BUGS
The
pthread_barrierattr_getpshared() and
pthread_barrierattr_setpshared() functions are hidden by
default since only thread shared attributes are supported.