1/* Copyright (C) 2003-2016 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 <futex-internal.h>
23#include <pthread.h>
24#include <pthreadP.h>
25#include <sys/time.h>
26#include <stdbool.h>
27
28
29/* Try to acquire write lock for RWLOCK or return after specfied time. */
30int
31pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
32 const struct timespec *abstime)
33{
34 int result = 0;
35 bool wake_readers = false;
36 int futex_shared =
37 rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
38
39 /* Make sure we are alone. */
40 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
41
42 while (1)
43 {
44 int err;
45
46 /* Get the rwlock if there is no writer and no reader. */
47 if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
48 {
49 /* Mark self as writer. */
50 rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
51 break;
52 }
53
54 /* Make sure we are not holding the rwlock as a writer. This is
55 a deadlock situation we recognize and report. */
56 if (__builtin_expect (rwlock->__data.__writer
57 == THREAD_GETMEM (THREAD_SELF, tid), 0))
58 {
59 result = EDEADLK;
60 break;
61 }
62
63 /* Make sure the passed in timeout value is valid. Ideally this
64 test would be executed once. But since it must not be
65 performed if we would not block at all simply moving the test
66 to the front is no option. Replicating all the code is
67 costly while this test is not. */
68 if (__builtin_expect (abstime->tv_nsec >= 1000000000
69 || abstime->tv_nsec < 0, 0))
70 {
71 result = EINVAL;
72 break;
73 }
74
75 /* Remember that we are a writer. */
76 if (++rwlock->__data.__nr_writers_queued == 0)
77 {
78 /* Overflow on number of queued writers. */
79 --rwlock->__data.__nr_writers_queued;
80 result = EAGAIN;
81 break;
82 }
83
84 int waitval = rwlock->__data.__writer_wakeup;
85
86 /* Free the lock. */
87 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
88
89 /* Wait for the writer or reader(s) to finish. We handle ETIMEDOUT
90 below; on other return values, we decide how to continue based on
91 the state of the rwlock. */
92 err = futex_abstimed_wait (&rwlock->__data.__writer_wakeup, waitval,
93 abstime, futex_shared);
94
95 /* Get the lock. */
96 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
97
98 /* To start over again, remove the thread from the writer list. */
99 --rwlock->__data.__nr_writers_queued;
100
101 /* Did the futex call time out? */
102 if (err == ETIMEDOUT)
103 {
104 result = ETIMEDOUT;
105 /* If we prefer writers, it can have happened that readers blocked
106 for us to acquire the lock first. If we have timed out, we need
107 to wake such readers if there are any, and if there is no writer
108 currently (otherwise, the writer will take care of wake-up).
109 Likewise, even if we prefer readers, we can be responsible for
110 wake-up (see pthread_rwlock_unlock) if no reader or writer has
111 acquired the lock. We have timed out and thus not consumed a
112 futex wake-up; therefore, if there is no other blocked writer
113 that would consume the wake-up and thus take over responsibility,
114 we need to wake blocked readers. */
115 if ((!PTHREAD_RWLOCK_PREFER_READER_P (rwlock)
116 || ((rwlock->__data.__nr_readers == 0)
117 && (rwlock->__data.__nr_writers_queued == 0)))
118 && (rwlock->__data.__nr_readers_queued > 0)
119 && (rwlock->__data.__writer == 0))
120 {
121 ++rwlock->__data.__readers_wakeup;
122 wake_readers = true;
123 }
124 break;
125 }
126 }
127
128 /* We are done, free the lock. */
129 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
130
131 /* Might be required after timeouts. */
132 if (wake_readers)
133 futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
134
135 return result;
136}
137