diff options
Diffstat (limited to 'nptl/pthread_rwlock_timedrdlock.c')
| -rw-r--r-- | nptl/pthread_rwlock_timedrdlock.c | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/nptl/pthread_rwlock_timedrdlock.c b/nptl/pthread_rwlock_timedrdlock.c new file mode 100644 index 0000000000..80ea83a3dd --- /dev/null +++ b/nptl/pthread_rwlock_timedrdlock.c @@ -0,0 +1,137 @@ +/* Copyright (C) 2003, 2004 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +#include <errno.h> +#include <sysdep.h> +#include <lowlevellock.h> +#include <pthread.h> +#include <pthreadP.h> + + +/* Try to acquire read lock for RWLOCK or return after specfied time. */ +int +pthread_rwlock_timedrdlock (rwlock, abstime) + pthread_rwlock_t *rwlock; + const struct timespec *abstime; +{ + int result = 0; + + /* Make sure we are along. */ + lll_mutex_lock(rwlock->__data.__lock); + + while (1) + { + int err; + + /* Get the rwlock if there is no writer... */ + if (rwlock->__data.__writer == 0 + /* ...and if either no writer is waiting or we prefer readers. */ + && (!rwlock->__data.__nr_writers_queued + || rwlock->__data.__flags == 0)) + { + /* Increment the reader counter. Avoid overflow. */ + if (++rwlock->__data.__nr_readers == 0) + { + /* Overflow on number of readers. */ + --rwlock->__data.__nr_readers; + result = EAGAIN; + } + + break; + } + + /* Make sure we are not holding the rwlock as a writer. This is + a deadlock situation we recognize and report. */ + if (__builtin_expect (rwlock->__data.__writer + == THREAD_GETMEM (THREAD_SELF, tid), 0)) + { + result = EDEADLK; + break; + } + + /* Make sure the passed in timeout value is valid. Ideally this + test would be executed once. But since it must not be + performed if we would not block at all simply moving the test + to the front is no option. Replicating all the code is + costly while this test is not. */ + if (__builtin_expect (abstime->tv_nsec >= 1000000000 + || abstime->tv_nsec < 0, 0)) + { + result = EINVAL; + break; + } + + /* Get the current time. So far we support only one clock. */ + struct timeval tv; + (void) gettimeofday (&tv, NULL); + + /* Convert the absolute timeout value to a relative timeout. */ + struct timespec rt; + rt.tv_sec = abstime->tv_sec - tv.tv_sec; + rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000; + if (rt.tv_nsec < 0) + { + rt.tv_nsec += 1000000000; + --rt.tv_sec; + } + /* Did we already time out? */ + if (rt.tv_sec < 0) + { + /* Yep, return with an appropriate error. */ + result = ETIMEDOUT; + break; + } + + /* Remember that we are a reader. */ + if (++rwlock->__data.__nr_readers_queued == 0) + { + /* Overflow on number of queued readers. */ + --rwlock->__data.__nr_readers_queued; + result = EAGAIN; + break; + } + + int waitval = rwlock->__data.__readers_wakeup; + + /* Free the lock. */ + lll_mutex_unlock (rwlock->__data.__lock); + + /* Wait for the writer to finish. */ + err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup, + waitval, &rt); + + /* Get the lock. */ + lll_mutex_lock (rwlock->__data.__lock); + + --rwlock->__data.__nr_readers_queued; + + /* Did the futex call time out? */ + if (err == -ETIMEDOUT) + { + /* Yep, report it. */ + result = ETIMEDOUT; + break; + } + } + + /* We are done, free the lock. */ + lll_mutex_unlock (rwlock->__data.__lock); + + return result; +} |