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bfff8b1b | 1 | /* Copyright (C) 2003-2017 Free Software Foundation, Inc. |
a88c9263 UD |
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 | |
59ba27a6 PE |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
a88c9263 UD |
18 | |
19 | #include <errno.h> | |
20 | #include <sysdep.h> | |
21 | #include <lowlevellock.h> | |
a2f0363f | 22 | #include <futex-internal.h> |
a88c9263 UD |
23 | #include <pthread.h> |
24 | #include <pthreadP.h> | |
6af246cf | 25 | #include <sys/time.h> |
3c9c61fe | 26 | #include <stdbool.h> |
a88c9263 UD |
27 | |
28 | ||
29 | /* Try to acquire write lock for RWLOCK or return after specfied time. */ | |
30 | int | |
f63f2bfd JM |
31 | pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock, |
32 | const struct timespec *abstime) | |
a88c9263 UD |
33 | { |
34 | int result = 0; | |
3c9c61fe | 35 | bool wake_readers = false; |
a2f0363f TR |
36 | int futex_shared = |
37 | rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED; | |
a88c9263 | 38 | |
c5be0f71 | 39 | /* Make sure we are alone. */ |
e51deae7 | 40 | lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 UD |
41 | |
42 | while (1) | |
43 | { | |
be095ffa UD |
44 | int err; |
45 | ||
a88c9263 | 46 | /* Get the rwlock if there is no writer and no reader. */ |
b80770b2 | 47 | if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0) |
a88c9263 UD |
48 | { |
49 | /* Mark self as writer. */ | |
4ad0bbf4 | 50 | rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid); |
a88c9263 UD |
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. */ | |
4ad0bbf4 UD |
56 | if (__builtin_expect (rwlock->__data.__writer |
57 | == THREAD_GETMEM (THREAD_SELF, tid), 0)) | |
a88c9263 UD |
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. */ | |
46f4c578 | 68 | if (__builtin_expect (abstime->tv_nsec >= 1000000000 |
f3a19754 | 69 | || abstime->tv_nsec < 0, 0)) |
a88c9263 UD |
70 | { |
71 | result = EINVAL; | |
72 | break; | |
73 | } | |
74 | ||
a88c9263 UD |
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 | ||
18a53579 UD |
84 | int waitval = rwlock->__data.__writer_wakeup; |
85 | ||
a88c9263 | 86 | /* Free the lock. */ |
e51deae7 | 87 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 | 88 | |
a2f0363f TR |
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); | |
a88c9263 UD |
94 | |
95 | /* Get the lock. */ | |
e51deae7 | 96 | lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 UD |
97 | |
98 | /* To start over again, remove the thread from the writer list. */ | |
99 | --rwlock->__data.__nr_writers_queued; | |
a88c9263 UD |
100 | |
101 | /* Did the futex call time out? */ | |
a2f0363f | 102 | if (err == ETIMEDOUT) |
a88c9263 UD |
103 | { |
104 | result = ETIMEDOUT; | |
3c9c61fe TR |
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 | |
b634486d TR |
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))) | |
3c9c61fe TR |
118 | && (rwlock->__data.__nr_readers_queued > 0) |
119 | && (rwlock->__data.__writer == 0)) | |
120 | { | |
121 | ++rwlock->__data.__readers_wakeup; | |
122 | wake_readers = true; | |
123 | } | |
a88c9263 UD |
124 | break; |
125 | } | |
126 | } | |
127 | ||
128 | /* We are done, free the lock. */ | |
e51deae7 | 129 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 | 130 | |
3c9c61fe TR |
131 | /* Might be required after timeouts. */ |
132 | if (wake_readers) | |
a2f0363f | 133 | futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared); |
3c9c61fe | 134 | |
a88c9263 UD |
135 | return result; |
136 | } |