1 /* Copyright (C) 2003,2004,2007,2011 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>
26 /* Acquire read lock for RWLOCK. */
28 __pthread_rwlock_rdlock (rwlock
)
29 pthread_rwlock_t
*rwlock
;
33 /* Make sure we are alone. */
34 lll_lock (rwlock
->__data
.__lock
, rwlock
->__data
.__shared
);
38 /* Get the rwlock if there is no writer... */
39 if (rwlock
->__data
.__writer
== 0
40 /* ...and if either no writer is waiting or we prefer readers. */
41 && (!rwlock
->__data
.__nr_writers_queued
42 || PTHREAD_RWLOCK_PREFER_READER_P (rwlock
)))
44 /* Increment the reader counter. Avoid overflow. */
45 if (__builtin_expect (++rwlock
->__data
.__nr_readers
== 0, 0))
47 /* Overflow on number of readers. */
48 --rwlock
->__data
.__nr_readers
;
55 /* Make sure we are not holding the rwlock as a writer. This is
56 a deadlock situation we recognize and report. */
57 if (__builtin_expect (rwlock
->__data
.__writer
58 == THREAD_GETMEM (THREAD_SELF
, tid
), 0))
64 /* Remember that we are a reader. */
65 if (__builtin_expect (++rwlock
->__data
.__nr_readers_queued
== 0, 0))
67 /* Overflow on number of queued readers. */
68 --rwlock
->__data
.__nr_readers_queued
;
73 int waitval
= rwlock
->__data
.__readers_wakeup
;
76 lll_unlock (rwlock
->__data
.__lock
, rwlock
->__data
.__shared
);
78 /* Wait for the writer to finish. */
79 lll_futex_wait (&rwlock
->__data
.__readers_wakeup
, waitval
,
80 rwlock
->__data
.__shared
);
83 lll_lock (rwlock
->__data
.__lock
, rwlock
->__data
.__shared
);
85 --rwlock
->__data
.__nr_readers_queued
;
88 /* We are done, free the lock. */
89 lll_unlock (rwlock
->__data
.__lock
, rwlock
->__data
.__shared
);
94 weak_alias (__pthread_rwlock_rdlock
, pthread_rwlock_rdlock
)
95 strong_alias (__pthread_rwlock_rdlock
, __pthread_rwlock_rdlock_internal
)