1 | /* Acquire a rwlock for reading. Generic version. |
2 | Copyright (C) 2002-2022 Free Software Foundation, Inc. |
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 |
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 | <https://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <pthread.h> |
20 | #include <assert.h> |
21 | #include <time.h> |
22 | |
23 | #include <pt-internal.h> |
24 | |
25 | /* Acquire the rwlock *RWLOCK for reading blocking until *ABSTIME if |
26 | it is already held. As a GNU extension, if TIMESPEC is NULL then |
27 | wait forever. */ |
28 | int |
29 | __pthread_rwlock_timedrdlock_internal (struct __pthread_rwlock *rwlock, |
30 | clockid_t clockid, |
31 | const struct timespec *abstime) |
32 | { |
33 | error_t err; |
34 | int drain; |
35 | struct __pthread *self; |
36 | |
37 | __pthread_spin_wait (&rwlock->__lock); |
38 | if (__pthread_spin_trylock (&rwlock->__held) == 0) |
39 | /* Successfully acquired the lock. */ |
40 | { |
41 | assert (rwlock->__readerqueue == 0); |
42 | assert (rwlock->__writerqueue == 0); |
43 | assert (rwlock->__readers == 0); |
44 | |
45 | rwlock->__readers = 1; |
46 | __pthread_spin_unlock (&rwlock->__lock); |
47 | return 0; |
48 | } |
49 | else |
50 | /* Lock is held, but is held by a reader? */ |
51 | if (rwlock->__readers > 0) |
52 | /* Just add ourself to number of readers. */ |
53 | { |
54 | assert (rwlock->__readerqueue == 0); |
55 | rwlock->__readers++; |
56 | __pthread_spin_unlock (&rwlock->__lock); |
57 | return 0; |
58 | } |
59 | |
60 | /* The lock is busy. */ |
61 | |
62 | /* Better be blocked by a writer. */ |
63 | assert (rwlock->__readers == 0); |
64 | |
65 | if (abstime != NULL && ! valid_nanoseconds (ns: abstime->tv_nsec)) |
66 | { |
67 | __pthread_spin_unlock (&rwlock->__lock); |
68 | return EINVAL; |
69 | } |
70 | |
71 | self = _pthread_self (); |
72 | |
73 | /* Add ourself to the queue. */ |
74 | __pthread_enqueue (&rwlock->__readerqueue, self); |
75 | __pthread_spin_unlock (&rwlock->__lock); |
76 | |
77 | /* Block the thread. */ |
78 | if (abstime != NULL) |
79 | err = __pthread_timedblock (self, abstime, clockid); |
80 | else |
81 | { |
82 | err = 0; |
83 | __pthread_block (self); |
84 | } |
85 | |
86 | __pthread_spin_wait (&rwlock->__lock); |
87 | if (self->prevp == NULL) |
88 | /* Another thread removed us from the queue, which means a wakeup message |
89 | has been sent. It was either consumed while we were blocking, or |
90 | queued after we timed out and before we acquired the rwlock lock, in |
91 | which case the message queue must be drained. */ |
92 | drain = err ? 1 : 0; |
93 | else |
94 | { |
95 | /* We're still in the queue. Noone attempted to wake us up, i.e. we |
96 | timed out. */ |
97 | __pthread_dequeue (self); |
98 | drain = 0; |
99 | } |
100 | __pthread_spin_unlock (&rwlock->__lock); |
101 | |
102 | if (drain) |
103 | __pthread_block (self); |
104 | |
105 | if (err) |
106 | { |
107 | assert (err == ETIMEDOUT); |
108 | return err; |
109 | } |
110 | |
111 | /* The reader count has already been increment by whoever woke us |
112 | up. */ |
113 | |
114 | assert (rwlock->__readers > 0); |
115 | |
116 | return 0; |
117 | } |
118 | |
119 | int |
120 | __pthread_rwlock_timedrdlock (struct __pthread_rwlock *rwlock, |
121 | const struct timespec *abstime) |
122 | { |
123 | return __pthread_rwlock_timedrdlock_internal (rwlock, CLOCK_REALTIME, abstime); |
124 | } |
125 | weak_alias (__pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock) |
126 | |
127 | int |
128 | __pthread_rwlock_clockrdlock (struct __pthread_rwlock *rwlock, |
129 | clockid_t clockid, |
130 | const struct timespec *abstime) |
131 | { |
132 | return __pthread_rwlock_timedrdlock_internal (rwlock, clockid, abstime); |
133 | } |
134 | weak_alias (__pthread_rwlock_clockrdlock, pthread_rwlock_clockrdlock) |
135 | |