| /* |
| Copyright 2005-2010 Intel Corporation. All Rights Reserved. |
| |
| This file is part of Threading Building Blocks. |
| |
| Threading Building Blocks is free software; you can redistribute it |
| and/or modify it under the terms of the GNU General Public License |
| version 2 as published by the Free Software Foundation. |
| |
| Threading Building Blocks 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. |
| |
| You should have received a copy of the GNU General Public License |
| along with Threading Building Blocks; if not, write to the Free Software |
| Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA |
| |
| As a special exception, you may use this file as part of a free software |
| library without restriction. Specifically, if other files instantiate |
| templates or use macros or inline functions from this file, or you compile |
| this file and link it with other files to produce an executable, this |
| file does not by itself cause the resulting executable to be covered by |
| the GNU General Public License. This exception does not however |
| invalidate any other reasons why the executable file might be covered by |
| the GNU General Public License. |
| */ |
| |
| #ifndef __TBB_spin_rw_mutex_H |
| #define __TBB_spin_rw_mutex_H |
| |
| #include "tbb/tbb_stddef.h" |
| |
| namespace tbb { |
| |
| //! Fast, unfair, spinning reader-writer lock with backoff and writer-preference |
| /** @ingroup synchronization */ |
| class spin_rw_mutex { |
| //! @cond INTERNAL |
| |
| //! Present so that 1.0 headers work with 1.1 dynamic library. |
| static void __TBB_EXPORTED_FUNC internal_itt_releasing(spin_rw_mutex *); |
| |
| //! Internal acquire write lock. |
| static bool __TBB_EXPORTED_FUNC internal_acquire_writer(spin_rw_mutex *); |
| |
| //! Out of line code for releasing a write lock. |
| /** This code is has debug checking and instrumentation for Intel(R) Thread Checker and Intel(R) Thread Profiler. */ |
| static void __TBB_EXPORTED_FUNC internal_release_writer(spin_rw_mutex *); |
| |
| //! Internal acquire read lock. |
| static void __TBB_EXPORTED_FUNC internal_acquire_reader(spin_rw_mutex *); |
| |
| //! Internal upgrade reader to become a writer. |
| static bool __TBB_EXPORTED_FUNC internal_upgrade(spin_rw_mutex *); |
| |
| //! Out of line code for downgrading a writer to a reader. |
| /** This code is has debug checking and instrumentation for Intel(R) Thread Checker and Intel(R) Thread Profiler. */ |
| static void __TBB_EXPORTED_FUNC internal_downgrade(spin_rw_mutex *); |
| |
| //! Internal release read lock. |
| static void __TBB_EXPORTED_FUNC internal_release_reader(spin_rw_mutex *); |
| |
| //! Internal try_acquire write lock. |
| static bool __TBB_EXPORTED_FUNC internal_try_acquire_writer(spin_rw_mutex *); |
| |
| //! Internal try_acquire read lock. |
| static bool __TBB_EXPORTED_FUNC internal_try_acquire_reader(spin_rw_mutex *); |
| |
| //! @endcond |
| public: |
| //! Construct unacquired mutex. |
| spin_rw_mutex() : state(0) {} |
| |
| #if TBB_DO_ASSERT |
| //! Destructor asserts if the mutex is acquired, i.e. state is zero. |
| ~spin_rw_mutex() { |
| __TBB_ASSERT( !state, "destruction of an acquired mutex"); |
| }; |
| #endif /* TBB_DO_ASSERT */ |
| |
| //! The scoped locking pattern |
| /** It helps to avoid the common problem of forgetting to release lock. |
| It also nicely provides the "node" for queuing locks. */ |
| class scoped_lock : private internal::no_copy { |
| public: |
| //! Construct lock that has not acquired a mutex. |
| /** Equivalent to zero-initialization of *this. */ |
| scoped_lock() : mutex(NULL) {} |
| |
| //! Acquire lock on given mutex. |
| /** Upon entry, *this should not be in the "have acquired a mutex" state. */ |
| scoped_lock( spin_rw_mutex& m, bool write = true ) : mutex(NULL) { |
| acquire(m, write); |
| } |
| |
| //! Release lock (if lock is held). |
| ~scoped_lock() { |
| if( mutex ) release(); |
| } |
| |
| //! Acquire lock on given mutex. |
| void acquire( spin_rw_mutex& m, bool write = true ) { |
| __TBB_ASSERT( !mutex, "holding mutex already" ); |
| is_writer = write; |
| mutex = &m; |
| if( write ) internal_acquire_writer(mutex); |
| else internal_acquire_reader(mutex); |
| } |
| |
| //! Upgrade reader to become a writer. |
| /** Returns true if the upgrade happened without re-acquiring the lock and false if opposite */ |
| bool upgrade_to_writer() { |
| __TBB_ASSERT( mutex, "lock is not acquired" ); |
| __TBB_ASSERT( !is_writer, "not a reader" ); |
| is_writer = true; |
| return internal_upgrade(mutex); |
| } |
| |
| //! Release lock. |
| void release() { |
| __TBB_ASSERT( mutex, "lock is not acquired" ); |
| spin_rw_mutex *m = mutex; |
| mutex = NULL; |
| if( is_writer ) { |
| #if TBB_DO_THREADING_TOOLS||TBB_DO_ASSERT |
| internal_release_writer(m); |
| #else |
| m->state = 0; |
| #endif /* TBB_DO_THREADING_TOOLS||TBB_DO_ASSERT */ |
| } else { |
| internal_release_reader(m); |
| } |
| }; |
| |
| //! Downgrade writer to become a reader. |
| bool downgrade_to_reader() { |
| #if TBB_DO_THREADING_TOOLS||TBB_DO_ASSERT |
| __TBB_ASSERT( mutex, "lock is not acquired" ); |
| __TBB_ASSERT( is_writer, "not a writer" ); |
| internal_downgrade(mutex); |
| #else |
| mutex->state = 4; // Bit 2 - reader, 00..00100 |
| #endif |
| is_writer = false; |
| |
| return true; |
| } |
| |
| //! Try acquire lock on given mutex. |
| bool try_acquire( spin_rw_mutex& m, bool write = true ) { |
| __TBB_ASSERT( !mutex, "holding mutex already" ); |
| bool result; |
| is_writer = write; |
| result = write? internal_try_acquire_writer(&m) |
| : internal_try_acquire_reader(&m); |
| if( result ) mutex = &m; |
| return result; |
| } |
| |
| private: |
| //! The pointer to the current mutex that is held, or NULL if no mutex is held. |
| spin_rw_mutex* mutex; |
| |
| //! True if holding a writer lock, false if holding a reader lock. |
| /** Not defined if not holding a lock. */ |
| bool is_writer; |
| }; |
| |
| private: |
| typedef uintptr_t state_t; |
| static const state_t WRITER = 1; |
| static const state_t WRITER_PENDING = 2; |
| static const state_t READERS = ~(WRITER | WRITER_PENDING); |
| static const state_t ONE_READER = 4; |
| static const state_t BUSY = WRITER | READERS; |
| /** Bit 0 = writer is holding lock |
| Bit 1 = request by a writer to acquire lock (hint to readers to wait) |
| Bit 2..N = number of readers holding lock */ |
| volatile state_t state; |
| }; |
| |
| } // namespace ThreadingBuildingBlocks |
| |
| #endif /* __TBB_spin_rw_mutex_H */ |