NAME

shmem_set_lock(3), shmem_clear_lock(3), shmem_test_lock(3) - Releases, locks, and tests a mutual exclusion memory lock.

SYNOPSIS

C or C++:

#include <mpp/shmem.h>
void shmem_clear_lock(volatile long *lock);
void shmem_set_lock(volatile long *lock);
int shmem_test_lock(volatile long *lock);

Fortran:

INCLUDE "mpp/shmem.fh"
INTEGER lock, SHMEM_TEST_LOCK
CALL SHMEM_CLEAR_LOCK(lock)
CALL SHMEM_SET_LOCK(lock)
I = SHMEM_TEST_LOCK(lock)

DESCRIPTION

The shmem_set_lock routine sets a mutual exclusion lock after waiting for the lock to be freed by any other PE currently holding the lock. Waiting PEs are assured of getting the lock in a first-come, first-served manner.

The shmem_clear_lock routine releases a lock previously set by shmem_set_lock after ensuring that all local and remote stores initiated in the critical region are complete.

The shmem_test_lock function sets a mutual exclusion lock only if it is currently cleared. By using this function, a PE can avoid blocking on a set lock. If the lock is currently set, the function returns without waiting. These routines are appropriate for protecting a critical region from simultaneous update by multiple PEs. They accept the following arguments:

lock

A symmetric data object that is a scalar variable or an array of length 1. This data object must be set to 0 on all processing elements (PEs) prior to the first use. lock must be of type integer. If you are using Fortran, it must be of default kind.

NOTES

The term symmetric data object is defined on intro_shmem(3).

RETURN VALUES

The shmem_test_lock function returns 0 if the lock was originally cleared and this call was able to set the lock. A value of 1 is returned if the lock had been set and the call returned without waiting to set the lock.

SEE ALSO

intro_shmem(3)