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33574c17 | 1 | /* Acquire a rwlock for reading. Generic version. |
04277e02 | 2 | Copyright (C) 2002-2019 Free Software Foundation, Inc. |
33574c17 ST |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
ad2b41bf ST |
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. | |
33574c17 ST |
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 | |
ad2b41bf | 13 | Lesser General Public License for more details. |
33574c17 | 14 | |
ad2b41bf ST |
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/>. */ | |
33574c17 ST |
18 | |
19 | #include <pthread.h> | |
20 | #include <assert.h> | |
21 | ||
22 | #include <pt-internal.h> | |
23 | ||
24 | /* Acquire the rwlock *RWLOCK for reading blocking until *ABSTIME if | |
25 | it is already held. As a GNU extension, if TIMESPEC is NULL then | |
26 | wait forever. */ | |
27 | int | |
28 | __pthread_rwlock_timedrdlock_internal (struct __pthread_rwlock *rwlock, | |
29 | const struct timespec *abstime) | |
30 | { | |
31 | error_t err; | |
32 | int drain; | |
33 | struct __pthread *self; | |
34 | ||
35 | __pthread_spin_lock (&rwlock->__lock); | |
36 | if (__pthread_spin_trylock (&rwlock->__held) == 0) | |
37 | /* Successfully acquired the lock. */ | |
38 | { | |
39 | assert (rwlock->__readerqueue == 0); | |
40 | assert (rwlock->__writerqueue == 0); | |
41 | assert (rwlock->__readers == 0); | |
42 | ||
43 | rwlock->__readers = 1; | |
44 | __pthread_spin_unlock (&rwlock->__lock); | |
45 | return 0; | |
46 | } | |
47 | else | |
48 | /* Lock is held, but is held by a reader? */ | |
49 | if (rwlock->__readers > 0) | |
50 | /* Just add ourself to number of readers. */ | |
51 | { | |
52 | assert (rwlock->__readerqueue == 0); | |
53 | rwlock->__readers++; | |
54 | __pthread_spin_unlock (&rwlock->__lock); | |
55 | return 0; | |
56 | } | |
57 | ||
58 | /* The lock is busy. */ | |
59 | ||
60 | /* Better be blocked by a writer. */ | |
61 | assert (rwlock->__readers == 0); | |
62 | ||
63 | if (abstime != NULL && (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)) | |
64 | return EINVAL; | |
65 | ||
66 | self = _pthread_self (); | |
67 | ||
68 | /* Add ourself to the queue. */ | |
69 | __pthread_enqueue (&rwlock->__readerqueue, self); | |
70 | __pthread_spin_unlock (&rwlock->__lock); | |
71 | ||
72 | /* Block the thread. */ | |
73 | if (abstime != NULL) | |
74 | err = __pthread_timedblock (self, abstime, CLOCK_REALTIME); | |
75 | else | |
76 | { | |
77 | err = 0; | |
78 | __pthread_block (self); | |
79 | } | |
80 | ||
81 | __pthread_spin_lock (&rwlock->__lock); | |
82 | if (self->prevp == NULL) | |
83 | /* Another thread removed us from the queue, which means a wakeup message | |
84 | has been sent. It was either consumed while we were blocking, or | |
85 | queued after we timed out and before we acquired the rwlock lock, in | |
86 | which case the message queue must be drained. */ | |
87 | drain = err ? 1 : 0; | |
88 | else | |
89 | { | |
90 | /* We're still in the queue. Noone attempted to wake us up, i.e. we | |
91 | timed out. */ | |
92 | __pthread_dequeue (self); | |
93 | drain = 0; | |
94 | } | |
95 | __pthread_spin_unlock (&rwlock->__lock); | |
96 | ||
97 | if (drain) | |
98 | __pthread_block (self); | |
99 | ||
100 | if (err) | |
101 | { | |
102 | assert (err == ETIMEDOUT); | |
103 | return err; | |
104 | } | |
105 | ||
106 | /* The reader count has already been increment by whoever woke us | |
107 | up. */ | |
108 | ||
109 | assert (rwlock->__readers > 0); | |
110 | ||
111 | return 0; | |
112 | } | |
113 | ||
114 | int | |
115 | __pthread_rwlock_timedrdlock (struct __pthread_rwlock *rwlock, | |
116 | const struct timespec *abstime) | |
117 | { | |
118 | return __pthread_rwlock_timedrdlock_internal (rwlock, abstime); | |
119 | } | |
120 | weak_alias (__pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock) |