spin_rw_mutex.h

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/*
    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_stddef.h"
#include "tbb_machine.h"
#include "tbb_profiling.h"

namespace tbb {

class spin_rw_mutex_v3;
typedef spin_rw_mutex_v3 spin_rw_mutex;


class spin_rw_mutex_v3 {

    bool __TBB_EXPORTED_METHOD internal_acquire_writer();


    void __TBB_EXPORTED_METHOD internal_release_writer();

    void __TBB_EXPORTED_METHOD internal_acquire_reader();

    bool __TBB_EXPORTED_METHOD internal_upgrade();


    void __TBB_EXPORTED_METHOD internal_downgrade();

    void __TBB_EXPORTED_METHOD internal_release_reader();

    bool __TBB_EXPORTED_METHOD internal_try_acquire_writer();

    bool __TBB_EXPORTED_METHOD internal_try_acquire_reader();

public:
    spin_rw_mutex_v3() : state(0) {
#if TBB_USE_THREADING_TOOLS
        internal_construct();
#endif
    }

#if TBB_USE_ASSERT

    ~spin_rw_mutex_v3() {
        __TBB_ASSERT( !state, "destruction of an acquired mutex");
    };
#endif /* TBB_USE_ASSERT */


    class scoped_lock : internal::no_copy {
    public:

        scoped_lock() : mutex(NULL), is_writer(false) {}

        scoped_lock( spin_rw_mutex& m, bool write = true ) : mutex(NULL) {
            acquire(m, write);
        }

        ~scoped_lock() {
            if( mutex ) release();
        }

        void acquire( spin_rw_mutex& m, bool write = true ) {
            __TBB_ASSERT( !mutex, "holding mutex already" );
            is_writer = write; 
            mutex = &m;
            if( write ) mutex->internal_acquire_writer();
            else        mutex->internal_acquire_reader();
        }


        bool upgrade_to_writer() {
            __TBB_ASSERT( mutex, "lock is not acquired" );
            __TBB_ASSERT( !is_writer, "not a reader" );
            is_writer = true; 
            return mutex->internal_upgrade();
        }

        void release() {
            __TBB_ASSERT( mutex, "lock is not acquired" );
            spin_rw_mutex *m = mutex; 
            mutex = NULL;
#if TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT
            if( is_writer ) m->internal_release_writer();
            else            m->internal_release_reader();
#else
            if( is_writer ) __TBB_AtomicAND( &m->state, READERS ); 
            else            __TBB_FetchAndAddWrelease( &m->state, -(intptr_t)ONE_READER);
#endif /* TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT */
        }

        bool downgrade_to_reader() {
#if TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT
            __TBB_ASSERT( mutex, "lock is not acquired" );
            __TBB_ASSERT( is_writer, "not a writer" );
            mutex->internal_downgrade();
#else
            __TBB_FetchAndAddW( &mutex->state, ((intptr_t)ONE_READER-WRITER));
#endif /* TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT */
            is_writer = false;

            return true;
        }

        bool try_acquire( spin_rw_mutex& m, bool write = true ) {
            __TBB_ASSERT( !mutex, "holding mutex already" );
            bool result;
            is_writer = write; 
            result = write? m.internal_try_acquire_writer()
                          : m.internal_try_acquire_reader();
            if( result ) 
                mutex = &m;
            return result;
        }

    private:
        spin_rw_mutex* mutex;


        bool is_writer;
    };

    // Mutex traits
    static const bool is_rw_mutex = true;
    static const bool is_recursive_mutex = false;
    static const bool is_fair_mutex = false;

    // ISO C++0x compatibility methods

    void lock() {internal_acquire_writer();}


    bool try_lock() {return internal_try_acquire_writer();}

    void unlock() {
#if TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT
        if( state&WRITER ) internal_release_writer();
        else               internal_release_reader();
#else
        if( state&WRITER ) __TBB_AtomicAND( &state, READERS ); 
        else               __TBB_FetchAndAddWrelease( &state, -(intptr_t)ONE_READER);
#endif /* TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT */
    }

    // Methods for reader locks that resemble ISO C++0x compatibility methods.

    void lock_read() {internal_acquire_reader();}


    bool try_lock_read() {return internal_try_acquire_reader();}

private:
    typedef intptr_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;

    state_t state;

    void __TBB_EXPORTED_METHOD internal_construct();
};

__TBB_DEFINE_PROFILING_SET_NAME(spin_rw_mutex)

} // namespace tbb

#endif /* __TBB_spin_rw_mutex_H */