summaryrefslogtreecommitdiff
path: root/condvar_check_need_init.c
blob: 1f6bba778cc9cf71ac4c2004dc7537b96bc15ead (plain)
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
86
87
88
89
90
91
92
93
94
/*
 * condvar_check_need_init.c
 *
 * Description:
 * This translation unit implements condition variables and their primitives.
 *
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads-win32 - POSIX Threads Library for Win32
 *      Copyright(C) 1998 John E. Bossom
 *      Copyright(C) 1999,2002 Pthreads-win32 contributors
 * 
 *      Contact Email: rpj@ise.canberra.edu.au
 * 
 *      The current list of contributors is contained
 *      in the file CONTRIBUTORS included with the source
 *      code distribution. The list can also be seen at the
 *      following World Wide Web location:
 *      http://sources.redhat.com/pthreads-win32/contributors.html
 * 
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation; either
 *      version 2 of the License, or (at your option) any later version.
 * 
 *      This library is distributed in the hope that it will be useful,
 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *      Lesser General Public License for more details.
 * 
 *      You should have received a copy of the GNU Lesser General Public
 *      License along with this library in the file COPYING.LIB;
 *      if not, write to the Free Software Foundation, Inc.,
 *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include "pthread.h"
#include "implement.h"


static INLINE int
ptw32_cond_check_need_init (pthread_cond_t *cond)
{
  int result = 0;

  /*
   * The following guarded test is specifically for statically
   * initialised condition variables (via PTHREAD_OBJECT_INITIALIZER).
   *
   * Note that by not providing this synchronisation we risk
   * introducing race conditions into applications which are
   * correctly written.
   *
   * Approach
   * --------
   * We know that static condition variables will not be PROCESS_SHARED
   * so we can serialise access to internal state using
   * Win32 Critical Sections rather than Win32 Mutexes.
   *
   * If using a single global lock slows applications down too much,
   * multiple global locks could be created and hashed on some random
   * value associated with each mutex, the pointer perhaps. At a guess,
   * a good value for the optimal number of global locks might be
   * the number of processors + 1.
   *
   */
  EnterCriticalSection(&ptw32_cond_test_init_lock);

  /*
   * We got here possibly under race
   * conditions. Check again inside the critical section.
   * If a static cv has been destroyed, the application can
   * re-initialise it only by calling pthread_cond_init()
   * explicitly.
   */
  if (*cond == PTHREAD_COND_INITIALIZER)
    {
      result = pthread_cond_init(cond, NULL);
    }
  else if (*cond == NULL)
    {
      /*
       * The cv has been destroyed while we were waiting to
       * initialise it, so the operation that caused the
       * auto-initialisation should fail.
       */
      result = EINVAL;
    }

  LeaveCriticalSection(&ptw32_cond_test_init_lock);

  return result;
}