projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 644eff0c | 1 | /* Copyright (C) 2003, 2004 Free Software Foundation, Inc. |
| a88c9263 UD |
2 | This file is part of the GNU C Library. |
| 3 | Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003. | |
| 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, write to the Free | |
| 17 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |
| 18 | 02111-1307 USA. */ | |
| 19 | ||
| 20 | #include <errno.h> | |
| 21 | #include <sysdep.h> | |
| 22 | #include <lowlevellock.h> | |
| 23 | #include <pthread.h> | |
| 24 | #include <pthreadP.h> | |
| 25 | ||
| 26 | ||
| 27 | /* Acquire read lock for RWLOCK. */ | |
| 28 | int | |
| 29 | __pthread_rwlock_rdlock (rwlock) | |
| 30 | pthread_rwlock_t *rwlock; | |
| 31 | { | |
| 32 | int result = 0; | |
| 33 | ||
| 34 | /* Make sure we are along. */ | |
| 35 | lll_mutex_lock (rwlock->__data.__lock); | |
| 36 | ||
| 37 | while (1) | |
| 38 | { | |
| 39 | /* Get the rwlock if there is no writer... */ | |
| 40 | if (rwlock->__data.__writer == 0 | |
| 41 | /* ...and if either no writer is waiting or we prefer readers. */ | |
| 42 | && (!rwlock->__data.__nr_writers_queued | |
| 43 | || rwlock->__data.__flags == 0)) | |
| 44 | { | |
| 45 | /* Increment the reader counter. Avoid overflow. */ | |
| 46 | if (__builtin_expect (++rwlock->__data.__nr_readers == 0, 0)) | |
| 47 | { | |
| 48 | /* Overflow on number of readers. */ | |
| 49 | --rwlock->__data.__nr_readers; | |
| 50 | result = EAGAIN; | |
| 51 | } | |
| 52 | ||
| 53 | break; | |
| 54 | } | |
| 55 | ||
| 56 | /* Make sure we are not holding the rwlock as a writer. This is | |
| 57 | a deadlock situation we recognize and report. */ | |
| 4ad0bbf4 UD |
58 | if (__builtin_expect (rwlock->__data.__writer |
| 59 | == THREAD_GETMEM (THREAD_SELF, tid), 0)) | |
| a88c9263 UD |
60 | { |
| 61 | result = EDEADLK; | |
| 62 | break; | |
| 63 | } | |
| 64 | ||
| 65 | /* Remember that we are a reader. */ | |
| 66 | if (__builtin_expect (++rwlock->__data.__nr_readers_queued == 0, 0)) | |
| 67 | { | |
| 68 | /* Overflow on number of queued readers. */ | |
| 69 | --rwlock->__data.__nr_readers_queued; | |
| 70 | result = EAGAIN; | |
| 71 | break; | |
| 72 | } | |
| 73 | ||
| 18a53579 UD |
74 | int waitval = rwlock->__data.__readers_wakeup; |
| 75 | ||
| a88c9263 UD |
76 | /* Free the lock. */ |
| 77 | lll_mutex_unlock (rwlock->__data.__lock); | |
| 78 | ||
| 79 | /* Wait for the writer to finish. */ | |
| 18a53579 | 80 | lll_futex_wait (&rwlock->__data.__readers_wakeup, waitval); |
| a88c9263 UD |
81 | |
| 82 | /* Get the lock. */ | |
| 83 | lll_mutex_lock (rwlock->__data.__lock); | |
| 644eff0c UD |
84 | |
| 85 | --rwlock->__data.__nr_readers_queued; | |
| a88c9263 UD |
86 | } |
| 87 | ||
| 88 | /* We are done, free the lock. */ | |
| 89 | lll_mutex_unlock (rwlock->__data.__lock); | |
| 90 | ||
| 91 | return result; | |
| 92 | } | |
| 93 | ||
| 94 | weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock) | |
| 95 | strong_alias (__pthread_rwlock_rdlock, __pthread_rwlock_rdlock_internal) |