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135 lines
3.8 KiB
C
135 lines
3.8 KiB
C
/* Acquire a rwlock for reading. Generic version.
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Copyright (C) 2002-2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <pthread.h>
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#include <assert.h>
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#include <time.h>
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#include <pt-internal.h>
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/* Acquire the rwlock *RWLOCK for reading blocking until *ABSTIME if
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it is already held. As a GNU extension, if TIMESPEC is NULL then
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wait forever. */
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int
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__pthread_rwlock_timedrdlock_internal (struct __pthread_rwlock *rwlock,
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clockid_t clockid,
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const struct timespec *abstime)
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{
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error_t err;
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int drain;
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struct __pthread *self;
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__pthread_spin_wait (&rwlock->__lock);
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if (__pthread_spin_trylock (&rwlock->__held) == 0)
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/* Successfully acquired the lock. */
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{
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assert (rwlock->__readerqueue == 0);
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assert (rwlock->__writerqueue == 0);
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assert (rwlock->__readers == 0);
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rwlock->__readers = 1;
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__pthread_spin_unlock (&rwlock->__lock);
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return 0;
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}
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else
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/* Lock is held, but is held by a reader? */
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if (rwlock->__readers > 0)
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/* Just add ourself to number of readers. */
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{
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assert (rwlock->__readerqueue == 0);
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rwlock->__readers++;
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__pthread_spin_unlock (&rwlock->__lock);
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return 0;
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}
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/* The lock is busy. */
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/* Better be blocked by a writer. */
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assert (rwlock->__readers == 0);
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if (abstime != NULL && ! valid_nanoseconds (abstime->tv_nsec))
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{
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__pthread_spin_unlock (&rwlock->__lock);
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return EINVAL;
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}
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self = _pthread_self ();
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/* Add ourself to the queue. */
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__pthread_enqueue (&rwlock->__readerqueue, self);
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__pthread_spin_unlock (&rwlock->__lock);
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/* Block the thread. */
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if (abstime != NULL)
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err = __pthread_timedblock (self, abstime, clockid);
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else
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{
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err = 0;
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__pthread_block (self);
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}
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__pthread_spin_wait (&rwlock->__lock);
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if (self->prevp == NULL)
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/* Another thread removed us from the queue, which means a wakeup message
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has been sent. It was either consumed while we were blocking, or
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queued after we timed out and before we acquired the rwlock lock, in
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which case the message queue must be drained. */
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drain = err ? 1 : 0;
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else
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{
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/* We're still in the queue. No one attempted to wake us up, i.e. we
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timed out. */
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__pthread_dequeue (self);
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drain = 0;
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}
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__pthread_spin_unlock (&rwlock->__lock);
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if (drain)
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__pthread_block (self);
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if (err)
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{
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assert (err == ETIMEDOUT);
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return err;
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}
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/* The reader count has already been increment by whoever woke us
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up. */
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assert (rwlock->__readers > 0);
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return 0;
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}
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int
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__pthread_rwlock_timedrdlock (struct __pthread_rwlock *rwlock,
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const struct timespec *abstime)
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{
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return __pthread_rwlock_timedrdlock_internal (rwlock, CLOCK_REALTIME, abstime);
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}
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weak_alias (__pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock)
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int
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__pthread_rwlock_clockrdlock (struct __pthread_rwlock *rwlock,
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clockid_t clockid,
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const struct timespec *abstime)
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{
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return __pthread_rwlock_timedrdlock_internal (rwlock, clockid, abstime);
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}
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weak_alias (__pthread_rwlock_clockrdlock, pthread_rwlock_clockrdlock)
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