/* Unlock a rwlock. Generic version. Copyright (C) 2000,02 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 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 Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with the GNU C Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include #include /* Unlock *RWLOCK, rescheduling a waiting writer thread or, if there are no threads waiting for a write lock, rescheduling the reader threads. */ int pthread_rwlock_unlock (pthread_rwlock_t *rwlock) { struct __pthread *wakeup; __pthread_spin_lock (&rwlock->__lock); assert (__pthread_spin_trylock (&rwlock->__held) == EBUSY); if (rwlock->readers > 1) /* There are other readers. */ { rwlock->readers --; __pthread_spin_unlock (&rwlock->__lock); return 0; } if (rwlock->readers == 1) /* Last reader. */ rwlock->readers = 0; /* Wake someone else up. Try the writer queue first, then the reader queue if that is empty. */ if (rwlock->writerqueue) { wakeup = rwlock->writerqueue; __pthread_dequeue (wakeup); /* We do not unlock RWLOCK->held: we are transferring the ownership to the thread that we are waking up. */ __pthread_spin_unlock (&rwlock->__lock); __pthread_wakeup (wakeup); return 0; } if (rwlock->readerqueue) { __pthread_queue_iterate (rwlock->readerqueue, wakeup) rwlock->readers ++; wakeup = rwlock->readerqueue; rwlock->readerqueue = 0; __pthread_spin_unlock (&rwlock->__lock); /* We can safely walk the list of waiting threads without holding the lock since it is now decoupled from the rwlock. */ __pthread_dequeuing_iterate (wakeup, wakeup) __pthread_wakeup (wakeup); return 0; } /* Noone is waiting. Just unlock it. */ __pthread_spin_unlock (&rwlock->__held); __pthread_spin_unlock (&rwlock->__lock); return 0; }