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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libitm/] [config/] [posix/] [rwlock.h] - Rev 866
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/* Copyright (C) 2009, 2011 Free Software Foundation, Inc. Contributed by Richard Henderson <rth@redhat.com>. This file is part of the GNU Transactional Memory Library (libitm). Libitm is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. Libitm 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 General Public License for more details. Under Section 7 of GPL version 3, you are granted additional permissions described in the GCC Runtime Library Exception, version 3.1, as published by the Free Software Foundation. You should have received a copy of the GNU General Public License and a copy of the GCC Runtime Library Exception along with this program; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see <http://www.gnu.org/licenses/>. */ #ifndef GTM_RWLOCK_H #define GTM_RWLOCK_H #include <pthread.h> #include "local_atomic" namespace GTM HIDDEN { struct gtm_thread; // This datastructure is the blocking, mutex-based side of the Dekker-style // reader-writer lock used to provide mutual exclusion between active and // serial transactions. It has similarities to POSIX pthread_rwlock_t except // that we also provide for upgrading a reader->writer lock, with a // positive indication of failure (another writer acquired the lock // before we were able to acquire). While the writer flag (a_writer below) is // global and protected by the mutex, there are per-transaction reader flags, // which are stored in a transaction's shared state. // See libitm's documentation for further details. // // In this implementation, writers are given highest priority access but // read-to-write upgrades do not have a higher priority than writers. class gtm_rwlock { pthread_mutex_t mutex; // Held if manipulating any field. pthread_cond_t c_readers; // Readers wait here pthread_cond_t c_writers; // Writers wait here for writers pthread_cond_t c_confirmed_writers; // Writers wait here for readers static const unsigned a_writer = 1; // An active writer. static const unsigned w_writer = 2; // The w_writers field != 0 static const unsigned w_reader = 4; // The w_readers field != 0 std::atomic<unsigned int> summary; // Bitmask of the above. unsigned int a_readers; // Nr active readers as observed by a writer unsigned int w_readers; // Nr waiting readers unsigned int w_writers; // Nr waiting writers public: gtm_rwlock(); ~gtm_rwlock(); void read_lock (gtm_thread *tx); void read_unlock (gtm_thread *tx); void write_lock (); void write_unlock (); bool write_upgrade (gtm_thread *tx); void write_upgrade_finish (gtm_thread *tx); protected: bool write_lock_generic (gtm_thread *tx); }; } // namespace GTM #endif // GTM_RWLOCK_H
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