1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
|
.. _shmem_set_lock:
shmem_set_lock
==============
.. include_body
:ref:`shmem_set_lock`\ (3), :ref:`shmem_clear_lock`\ (3), :ref:`shmem_test_lock`\ (3) -
Releases, locks, and tests a mutual exclusion memory lock.
SYNOPSIS
--------
C or C++:
.. code-block:: 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:
.. code-block:: 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 :ref:`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 :ref:`shmem_clear_lock` routine releases a lock previously set by
:ref:`shmem_set_lock` after ensuring that all local and remote stores initiated
in the critical region are complete.
The :ref:`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 :ref:`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.
.. seealso::
*intro_shmem*\ (3)
|
