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8ba6ad703c
900778283a ("htl: make pthread_spin_lock really spin") made
pthread_spin_lock really spin and not block, but the current users of
__pthread_spin_lock were assuming that it blocks, i.e. they use it as a
lightweight mutex fitting in just one int.
__pthread_spin_wait provides that support back.
99 lines
2.5 KiB
C
99 lines
2.5 KiB
C
/* Unlock a rwlock. Generic version.
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Copyright (C) 2000-2020 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 <pt-internal.h>
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/* Unlock *RWLOCK, rescheduling a waiting writer thread or, if there
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are no threads waiting for a write lock, rescheduling the reader
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threads. */
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int
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__pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
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{
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struct __pthread *wakeup;
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__pthread_spin_wait (&rwlock->__lock);
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assert (__pthread_spin_trylock (&rwlock->__held) == EBUSY);
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if (rwlock->__readers > 1)
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/* There are other readers. */
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{
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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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if (rwlock->__readers == 1)
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/* Last reader. */
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rwlock->__readers = 0;
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/* Wake someone else up. Try the writer queue first, then the
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reader queue if that is empty. */
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if (rwlock->__writerqueue)
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{
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wakeup = rwlock->__writerqueue;
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__pthread_dequeue (wakeup);
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/* We do not unlock RWLOCK->held: we are transferring the ownership
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to the thread that we are waking up. */
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__pthread_spin_unlock (&rwlock->__lock);
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__pthread_wakeup (wakeup);
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return 0;
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}
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if (rwlock->__readerqueue)
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{
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unsigned n = 0;
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__pthread_queue_iterate (rwlock->__readerqueue, wakeup)
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n++;
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{
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struct __pthread *wakeups[n];
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unsigned i = 0;
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__pthread_dequeuing_iterate (rwlock->__readerqueue, wakeup)
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wakeups[i++] = wakeup;
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rwlock->__readers += n;
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rwlock->__readerqueue = 0;
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__pthread_spin_unlock (&rwlock->__lock);
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for (i = 0; i < n; i++)
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__pthread_wakeup (wakeups[i]);
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}
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return 0;
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}
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/* Noone is waiting. Just unlock it. */
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__pthread_spin_unlock (&rwlock->__held);
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__pthread_spin_unlock (&rwlock->__lock);
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return 0;
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}
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weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock);
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