1/*
2 * pthread_rwlock_trywrlock.c
3 *
4 * Description:
5 * This translation unit implements read/write lock primitives.
6 *
7 * --------------------------------------------------------------------------
8 *
9 *      Pthreads-win32 - POSIX Threads Library for Win32
10 *      Copyright(C) 1998 John E. Bossom
11 *      Copyright(C) 1999,2005 Pthreads-win32 contributors
12 *
13 *      Contact Email: rpj@callisto.canberra.edu.au
14 *
15 *      The current list of contributors is contained
16 *      in the file CONTRIBUTORS included with the source
17 *      code distribution. The list can also be seen at the
18 *      following World Wide Web location:
19 *      http://sources.redhat.com/pthreads-win32/contributors.html
20 *
21 *      This library is free software; you can redistribute it and/or
22 *      modify it under the terms of the GNU Lesser General Public
23 *      License as published by the Free Software Foundation; either
24 *      version 2 of the License, or (at your option) any later version.
25 *
26 *      This library is distributed in the hope that it will be useful,
27 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
28 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
29 *      Lesser General Public License for more details.
30 *
31 *      You should have received a copy of the GNU Lesser General Public
32 *      License along with this library in the file COPYING.LIB;
33 *      if not, write to the Free Software Foundation, Inc.,
34 *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
35 */
36
37#include <limits.h>
38
39#include "pthread.h"
40#include "implement.h"
41
42int
43pthread_rwlock_trywrlock (pthread_rwlock_t * rwlock)
44{
45  int result, result1;
46  pthread_rwlock_t rwl;
47
48  if (rwlock == NULL || *rwlock == NULL)
49    {
50      return EINVAL;
51    }
52
53  /*
54   * We do a quick check to see if we need to do more work
55   * to initialise a static rwlock. We check
56   * again inside the guarded section of ptw32_rwlock_check_need_init()
57   * to avoid race conditions.
58   */
59  if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
60    {
61      result = ptw32_rwlock_check_need_init (rwlock);
62
63      if (result != 0 && result != EBUSY)
64	{
65	  return result;
66	}
67    }
68
69  rwl = *rwlock;
70
71  if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
72    {
73      return EINVAL;
74    }
75
76  if ((result = pthread_mutex_trylock (&(rwl->mtxExclusiveAccess))) != 0)
77    {
78      return result;
79    }
80
81  if ((result =
82       pthread_mutex_trylock (&(rwl->mtxSharedAccessCompleted))) != 0)
83    {
84      result1 = pthread_mutex_unlock (&(rwl->mtxExclusiveAccess));
85      return ((result1 != 0) ? result1 : result);
86    }
87
88  if (rwl->nExclusiveAccessCount == 0)
89    {
90      if (rwl->nCompletedSharedAccessCount > 0)
91	{
92	  rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
93	  rwl->nCompletedSharedAccessCount = 0;
94	}
95
96      if (rwl->nSharedAccessCount > 0)
97	{
98	  if ((result =
99	       pthread_mutex_unlock (&(rwl->mtxSharedAccessCompleted))) != 0)
100	    {
101	      (void) pthread_mutex_unlock (&(rwl->mtxExclusiveAccess));
102	      return result;
103	    }
104
105	  if ((result =
106	       pthread_mutex_unlock (&(rwl->mtxExclusiveAccess))) == 0)
107	    {
108	      result = EBUSY;
109	    }
110	}
111      else
112	{
113	  rwl->nExclusiveAccessCount = 1;
114	}
115    }
116  else
117    {
118      result = EBUSY;
119    }
120
121  return result;
122}
123