1 /* Copyright (C) 2003, 2004, 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 /* Try to acquire write lock for RWLOCK or return after specfied time. */
27 int
pthread_rwlock_timedwrlock(pthread_rwlock_t * rwlock,const struct timespec * abstime)28 pthread_rwlock_timedwrlock (
29 pthread_rwlock_t *rwlock,
30 const struct timespec *abstime)
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 int err;
40
41 /* Get the rwlock if there is no writer and no reader. */
42 if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
43 {
44 /* Mark self as writer. */
45 rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
46 break;
47 }
48
49 /* Make sure we are not holding the rwlock as a writer. This is
50 a deadlock situation we recognize and report. */
51 if (__builtin_expect (rwlock->__data.__writer
52 == THREAD_GETMEM (THREAD_SELF, tid), 0))
53 {
54 result = EDEADLK;
55 break;
56 }
57
58 /* Make sure the passed in timeout value is valid. Ideally this
59 test would be executed once. But since it must not be
60 performed if we would not block at all simply moving the test
61 to the front is no option. Replicating all the code is
62 costly while this test is not. */
63 if (__builtin_expect (abstime->tv_nsec >= 1000000000
64 || abstime->tv_nsec < 0, 0))
65 {
66 result = EINVAL;
67 break;
68 }
69
70 /* Get the current time. So far we support only one clock. */
71 struct timeval tv;
72 (void) gettimeofday (&tv, NULL);
73
74 /* Convert the absolute timeout value to a relative timeout. */
75 struct timespec rt;
76 rt.tv_sec = abstime->tv_sec - tv.tv_sec;
77 rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
78 if (rt.tv_nsec < 0)
79 {
80 rt.tv_nsec += 1000000000;
81 --rt.tv_sec;
82 }
83 /* Did we already time out? */
84 if (rt.tv_sec < 0)
85 {
86 result = ETIMEDOUT;
87 break;
88 }
89
90 /* Remember that we are a writer. */
91 if (++rwlock->__data.__nr_writers_queued == 0)
92 {
93 /* Overflow on number of queued writers. */
94 --rwlock->__data.__nr_writers_queued;
95 result = EAGAIN;
96 break;
97 }
98
99 int waitval = rwlock->__data.__writer_wakeup;
100
101 /* Free the lock. */
102 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
103
104 /* Wait for the writer or reader(s) to finish. */
105 err = lll_futex_timed_wait (&rwlock->__data.__writer_wakeup,
106 waitval, &rt, rwlock->__data.__shared);
107
108 /* Get the lock. */
109 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
110
111 /* To start over again, remove the thread from the writer list. */
112 --rwlock->__data.__nr_writers_queued;
113
114 /* Did the futex call time out? */
115 if (err == -ETIMEDOUT)
116 {
117 result = ETIMEDOUT;
118 break;
119 }
120 }
121
122 /* We are done, free the lock. */
123 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
124
125 return result;
126 }
127