1 | /* Unlock a rwlock. Generic version. |
2 | Copyright (C) 2000-2022 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 | |
21 | #include <pt-internal.h> |
22 | |
23 | /* Unlock *RWLOCK, rescheduling a waiting writer thread or, if there |
24 | are no threads waiting for a write lock, rescheduling the reader |
25 | threads. */ |
26 | int |
27 | __pthread_rwlock_unlock (pthread_rwlock_t *rwlock) |
28 | { |
29 | struct __pthread *wakeup; |
30 | |
31 | __pthread_spin_wait (&rwlock->__lock); |
32 | |
33 | assert (__pthread_spin_trylock (&rwlock->__held) == EBUSY); |
34 | |
35 | if (rwlock->__readers > 1) |
36 | /* There are other readers. */ |
37 | { |
38 | rwlock->__readers--; |
39 | __pthread_spin_unlock (&rwlock->__lock); |
40 | return 0; |
41 | } |
42 | |
43 | if (rwlock->__readers == 1) |
44 | /* Last reader. */ |
45 | rwlock->__readers = 0; |
46 | |
47 | |
48 | /* Wake someone else up. Try the writer queue first, then the |
49 | reader queue if that is empty. */ |
50 | |
51 | if (rwlock->__writerqueue) |
52 | { |
53 | wakeup = rwlock->__writerqueue; |
54 | __pthread_dequeue (wakeup); |
55 | |
56 | /* We do not unlock RWLOCK->held: we are transferring the ownership |
57 | to the thread that we are waking up. */ |
58 | |
59 | __pthread_spin_unlock (&rwlock->__lock); |
60 | __pthread_wakeup (wakeup); |
61 | |
62 | return 0; |
63 | } |
64 | |
65 | if (rwlock->__readerqueue) |
66 | { |
67 | unsigned n = 0; |
68 | |
69 | __pthread_queue_iterate (rwlock->__readerqueue, wakeup) |
70 | n++; |
71 | |
72 | { |
73 | struct __pthread *wakeups[n]; |
74 | unsigned i = 0; |
75 | |
76 | __pthread_dequeuing_iterate (rwlock->__readerqueue, wakeup) |
77 | wakeups[i++] = wakeup; |
78 | |
79 | rwlock->__readers += n; |
80 | rwlock->__readerqueue = 0; |
81 | |
82 | __pthread_spin_unlock (&rwlock->__lock); |
83 | |
84 | for (i = 0; i < n; i++) |
85 | __pthread_wakeup (wakeups[i]); |
86 | } |
87 | |
88 | return 0; |
89 | } |
90 | |
91 | |
92 | /* Noone is waiting. Just unlock it. */ |
93 | |
94 | __pthread_spin_unlock (&rwlock->__held); |
95 | __pthread_spin_unlock (&rwlock->__lock); |
96 | return 0; |
97 | } |
98 | weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock); |
99 | |