1 /* Copyright (C) 2003, 2007 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19 #include <errno.h>
20 #include <sysdep.h>
21 #include <lowlevellock.h>
22 #include <pthread.h>
23 #include <pthreadP.h>
24
25
26 /* Acquire write lock for RWLOCK. */
27 int
28 attribute_protected
__pthread_rwlock_wrlock(pthread_rwlock_t * rwlock)29 __pthread_rwlock_wrlock (
30 pthread_rwlock_t *rwlock)
31 {
32 int result = 0;
33
34 /* Make sure we are along. */
35 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
36
37 while (1)
38 {
39 /* Get the rwlock if there is no writer and no reader. */
40 if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
41 {
42 /* Mark self as writer. */
43 rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
44 break;
45 }
46
47 /* Make sure we are not holding the rwlock as a writer. This is
48 a deadlock situation we recognize and report. */
49 if (__builtin_expect (rwlock->__data.__writer
50 == THREAD_GETMEM (THREAD_SELF, tid), 0))
51 {
52 result = EDEADLK;
53 break;
54 }
55
56 /* Remember that we are a writer. */
57 if (++rwlock->__data.__nr_writers_queued == 0)
58 {
59 /* Overflow on number of queued writers. */
60 --rwlock->__data.__nr_writers_queued;
61 result = EAGAIN;
62 break;
63 }
64
65 int waitval = rwlock->__data.__writer_wakeup;
66
67 /* Free the lock. */
68 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
69
70 /* Wait for the writer or reader(s) to finish. */
71 lll_futex_wait (&rwlock->__data.__writer_wakeup, waitval,
72 rwlock->__data.__shared);
73
74 /* Get the lock. */
75 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
76
77 /* To start over again, remove the thread from the writer list. */
78 --rwlock->__data.__nr_writers_queued;
79 }
80
81 /* We are done, free the lock. */
82 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
83
84 return result;
85 }
86
87 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
88 strong_alias (__pthread_rwlock_wrlock, __pthread_rwlock_wrlock_internal)
89