1/* Try to 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
22#include <pt-internal.h>
23
24/* Try to acquire RWLOCK. */
25int
26pthread_rwlock_tryrdlock (struct __pthread_rwlock *rwlock)
27{
28 __pthread_spin_wait (&rwlock->__lock);
29 if (__pthread_spin_trylock (&rwlock->__held) == 0)
30 /* Successfully acquired the lock. */
31 {
32 assert (rwlock->__readerqueue == 0);
33 assert (rwlock->__writerqueue == 0);
34 assert (rwlock->__readers == 0);
35
36 rwlock->__readers = 1;
37 __pthread_spin_unlock (&rwlock->__lock);
38 return 0;
39 }
40 else
41 /* Lock is held, but is held by a reader? */
42 if (rwlock->__readers > 0)
43 {
44 assert (rwlock->__readerqueue == 0);
45 rwlock->__readers++;
46 __pthread_spin_unlock (&rwlock->__lock);
47 return 0;
48 }
49
50 /* The lock is busy. */
51
52 __pthread_spin_unlock (&rwlock->__lock);
53
54 return EBUSY;
55}
56

source code of glibc/sysdeps/htl/pt-rwlock-tryrdlock.c