1 /* Copyright (C) 2003-2013 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
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.
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.
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/>. */
21 #include <lowlevellock.h>
24 #include <stap-probe.h>
27 /* Acquire read lock for RWLOCK. */
29 __pthread_rwlock_rdlock (rwlock)
30 pthread_rwlock_t *rwlock;
34 LIBC_PROBE (rdlock_entry, 1, rwlock);
36 /* Make sure we are alone. */
37 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
41 /* Get the rwlock if there is no writer... */
42 if (rwlock->__data.__writer == 0
43 /* ...and if either no writer is waiting or we prefer readers. */
44 && (!rwlock->__data.__nr_writers_queued
45 || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
47 /* Increment the reader counter. Avoid overflow. */
48 if (__builtin_expect (++rwlock->__data.__nr_readers == 0, 0))
50 /* Overflow on number of readers. */
51 --rwlock->__data.__nr_readers;
55 LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
60 /* Make sure we are not holding the rwlock as a writer. This is
61 a deadlock situation we recognize and report. */
62 if (__builtin_expect (rwlock->__data.__writer
63 == THREAD_GETMEM (THREAD_SELF, tid), 0))
69 /* Remember that we are a reader. */
70 if (__builtin_expect (++rwlock->__data.__nr_readers_queued == 0, 0))
72 /* Overflow on number of queued readers. */
73 --rwlock->__data.__nr_readers_queued;
78 int waitval = rwlock->__data.__readers_wakeup;
81 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
83 /* Wait for the writer to finish. */
84 lll_futex_wait (&rwlock->__data.__readers_wakeup, waitval,
85 rwlock->__data.__shared);
88 lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
90 --rwlock->__data.__nr_readers_queued;
93 /* We are done, free the lock. */
94 lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
99 weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock)
100 hidden_def (__pthread_rwlock_rdlock)