Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of boost. Click here for the latest Boost documentation.

boost/thread/detail/read_write_lock.hpp

// Copyright (C)  2002-2003
// David Moore
//
// Original scoped_lock implementation
// Copyright (C) 2001
// William E. Kempf
//
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without fee,
// provided that the above copyright notice appear in all copies and
// that both that copyright notice and this permission notice appear
// in supporting documentation.  David Moore makes no representations
// about the suitability of this software for any purpose.
// It is provided "as is" without express or implied warranty.

#ifndef BOOST_READ_WRITE_LOCK_JDM031002_HPP
#define BOOST_READ_WRITE_LOCK_JDM031002_HPP

#include <boost/thread/detail/config.hpp>

#include <boost/utility.hpp>
#include <boost/thread/exceptions.hpp>
#include <boost/thread/detail/lock.hpp>

namespace boost {

struct xtime;

namespace read_write_lock_state {
    enum read_write_lock_state_enum
    {
        unlocked=0,
        read_locked=1,
        write_locked=2
    };
} //namespace read_write_lock_state

namespace detail {
namespace thread {

template <typename Mutex>
class read_write_lock_ops : private noncopyable
{
private:

    read_write_lock_ops() { }
    ~read_write_lock_ops() { }

public:

    typedef Mutex mutex_type;

    static void write_lock(Mutex& m)
    {
        m.do_write_lock();
    }
    static void read_lock(Mutex& m)
    {
        m.do_read_lock();
    }
    static void write_unlock(Mutex& m)
    {
        m.do_write_unlock();
    }
    static void read_unlock(Mutex &m)
    {
        m.do_read_unlock();
    }
    static bool try_write_lock(Mutex &m)
    {
        return m.do_try_write_lock();
    }
    static bool try_read_lock(Mutex &m)
    {
        return m.do_try_read_lock();
    }

    static bool timed_write_lock(Mutex &m,const xtime &xt)
    {
        return m.do_timed_write_lock(xt);
    }
    static bool timed_read_lock(Mutex &m,const xtime &xt)
    {
        return m.do_timed_read_lock(xt);
    }

    static void demote(Mutex & m)
    {
        m.do_demote_to_read_lock();
    }
    static bool try_demote(Mutex & m)
    {
        return m.do_try_demote_to_read_lock();
    }
    static bool timed_demote(Mutex & m,const xtime &xt)
    {
        return m.do_timed_demote_to_read_lock(xt);
    }

    static void promote(Mutex & m)
    {
        m.do_promote_to_write_lock();
    }
    static bool try_promote(Mutex & m)
    {
        return m.do_try_promote_to_write_lock();
    }
    static bool timed_promote(Mutex & m,const xtime &xt)
    {
        return m.do_timed_promote_to_write_lock(xt);
    }
};

template <typename ReadWriteMutex>
class scoped_read_write_lock : private noncopyable
{
public:

    typedef ReadWriteMutex mutex_type;

    scoped_read_write_lock(
        ReadWriteMutex& mx,
        read_write_lock_state::read_write_lock_state_enum initial_state)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initial_state == read_write_lock_state::read_locked)
            read_lock();
        else if (initial_state == read_write_lock_state::write_locked)
            write_lock();
    }

    ~scoped_read_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void read_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::read_lock(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    void write_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::write_lock(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    void unlock()
    {
        if (m_state == read_write_lock_state::unlocked) throw lock_error();
        if (m_state == read_write_lock_state::read_locked)
            read_write_lock_ops<ReadWriteMutex>::read_unlock(m_mutex);
        else //(m_state == read_write_lock_state::write_locked)
            read_write_lock_ops<ReadWriteMutex>::write_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }

    void demote(void)
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::demote(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    void promote(void)
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::promote(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    //If allow_unlock = true, set_lock always succeedes and
    //the function result indicates whether an unlock was required.
    //If allow_unlock = false, set_lock may fail;
    //the function result indicates whether it succeeded.
    bool set_lock(read_write_lock_state::read_write_lock_state_enum ls, bool allow_unlock = true)
    {
        bool result = !allow_unlock;

        if (m_state != ls)
        {
            if (m_state == read_write_lock_state::unlocked)
            {
                if (ls == read_write_lock_state::read_locked)
                    read_lock();
                else //(ls == read_write_lock_state::write_locked)
                    write_lock();
            }
            else //(m_state == read_write_lock_state::read_locked || m_state == read_write_lock_state::write_locked)
            {
                if (ls == read_write_lock_state::read_locked)
                    demote();
                else if (ls == read_write_lock_state::write_locked)
                {
                    if (allow_unlock)
                    {
                        result = true;
                        unlock();
                        write_lock();
                    }
                    else
                        result = false;
                }
                else //(ls == read_write_lock_state::unlocked)
                    unlock();
            }
        }

        return result;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }
  
    bool read_locked() const
    {
        return m_state == read_write_lock_state::read_locked;
    }
  
    bool write_locked() const
    {
        return m_state != read_write_lock_state::write_locked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

    read_write_lock_state::read_write_lock_state_enum state() const
    {
        return m_state;
    }
    
private:

    ReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename ReadWriteMutex>
class scoped_read_lock : private noncopyable
{
public:

    typedef ReadWriteMutex mutex_type;

    explicit scoped_read_lock(
        ReadWriteMutex& mx,
        bool initially_locked = true)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initially_locked)
            lock();
    }

    ~scoped_read_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::read_lock(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    void unlock()
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::read_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }
    
private:

    ReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename ReadWriteMutex>
class scoped_write_lock : private noncopyable
{
public:

    typedef ReadWriteMutex mutex_type;

    explicit scoped_write_lock(
        ReadWriteMutex& mx,
        bool initially_locked = true)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initially_locked)
            lock();
    }

    ~scoped_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::write_lock(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    void unlock()
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        read_write_lock_ops<ReadWriteMutex>::write_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }
    
private:

    ReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename TryReadWriteMutex>
class scoped_try_read_write_lock : private noncopyable
{
public:

    typedef TryReadWriteMutex mutex_type;
    
    scoped_try_read_write_lock(
        TryReadWriteMutex& mx,
        read_write_lock_state::read_write_lock_state_enum initial_state)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initial_state == read_write_lock_state::read_locked)
            read_lock();
        else if (initial_state == read_write_lock_state::write_locked)
            write_lock();
    }

    ~scoped_try_read_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void read_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::read_lock(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    bool try_read_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TryReadWriteMutex>::try_read_lock(m_mutex))
        {
            m_state = read_write_lock_state::read_locked;
            return true;
        }
        return false;
    }
   
    void write_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::write_lock(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    bool try_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TryReadWriteMutex>::try_write_lock(m_mutex))
        {
            m_state = read_write_lock_state::write_locked;
            return true;
        }
        return false;
    }

    void unlock()
    {
        if (m_state == read_write_lock_state::unlocked) throw lock_error();
        if (m_state == read_write_lock_state::read_locked)
            read_write_lock_ops<TryReadWriteMutex>::read_unlock(m_mutex);
        else //(m_state == read_write_lock_state::write_locked)
            read_write_lock_ops<TryReadWriteMutex>::write_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }

    void demote(void)
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::demote(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    bool try_demote(void)
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        return read_write_lock_ops<TryReadWriteMutex>::try_demote(m_mutex) ? (m_state = read_write_lock_state::read_locked, true) : false;
    }

    void promote(void)
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::promote(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    bool try_promote(void)
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        return read_write_lock_ops<TryReadWriteMutex>::try_promote(m_mutex) ? (m_state = read_write_lock_state::write_locked, true) : false;
    }

    //If allow_unlock = true, set_lock always succeedes and
    //the function result indicates whether an unlock was required.
    //If allow_unlock = false, set_lock may fail;
    //the function result indicates whether it succeeded.
    bool set_lock(read_write_lock_state::read_write_lock_state_enum ls, bool allow_unlock = true)
    {
        bool result = !allow_unlock;

        if (m_state != ls)
        {
            if (m_state == read_write_lock_state::unlocked)
            {
                if (ls == read_write_lock_state::read_locked)
                    read_lock();
                else //(ls == read_write_lock_state::write_locked)
                    write_lock();
            }
            else //(m_state == read_write_lock_state::read_locked || m_state == read_write_lock_state::write_locked)
            {
                if (ls == read_write_lock_state::read_locked)
                    demote();
                else if (ls == read_write_lock_state::write_locked)
                {
                    if (!try_promote())
                    {
                        if (allow_unlock)
                        {
                            result = true;
                            unlock();
                            write_lock();
                        }
                        else
                            result = false;
                    }
                }
                else //(ls == read_write_lock_state::unlocked)
                    unlock();
            }
        }

        return result;
    }

    bool try_set_lock(read_write_lock_state::read_write_lock_state_enum ls)
    {
        if (m_state != ls)
        {
            if (m_state == read_write_lock_state::unlocked)
            {
                if (ls == read_write_lock_state::read_locked)
                    return try_read_lock();
                else // (ls == read_write_lock_state::write_locked)
                    return try_write_lock();
            }
            else //(m_state == read_write_lock_state::read_locked || m_state == read_write_lock_state::write_locked)
            {
                if (ls == read_write_lock_state::read_locked)
                    return try_demote();
                else if (ls == read_write_lock_state::write_locked)
                    return try_promote();
                else //(ls == read_write_lock_state::unlocked)
                    return unlock(), true;
            }
        }
        else //(m_state == ls) 
            return true;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }
  
    bool read_locked() const
    {
        return m_state == read_write_lock_state::read_locked;
    }
  
    bool write_locked() const
    {
        return m_state != read_write_lock_state::write_locked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

    read_write_lock_state::read_write_lock_state_enum state() const
    {
        return m_state;
    }

private:

    TryReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename TryReadWriteMutex>
class scoped_try_read_lock : private noncopyable
{
public:

    typedef TryReadWriteMutex mutex_type;
    
    explicit scoped_try_read_lock(
        TryReadWriteMutex& mx,
        bool initially_locked = true)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initially_locked)
            lock();
    }

    ~scoped_try_read_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::read_lock(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    bool try_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TryReadWriteMutex>::try_read_lock(m_mutex))
        {
            m_state = read_write_lock_state::read_locked;
            return true;
        }
        return false;
    }

    void unlock()
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::read_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

private:

    TryReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename TryReadWriteMutex>
class scoped_try_write_lock : private noncopyable
{
public:

    typedef TryReadWriteMutex mutex_type;
    
    explicit scoped_try_write_lock(
        TryReadWriteMutex& mx,
        bool initially_locked = true)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initially_locked)
            lock();
    }

    ~scoped_try_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::write_lock(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    bool try_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TryReadWriteMutex>::try_write_lock(m_mutex))
        {
            m_state = read_write_lock_state::write_locked;
            return true;
        }
        return false;
    }

    void unlock()
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        read_write_lock_ops<TryReadWriteMutex>::write_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

private:

    TryReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename TimedReadWriteMutex>
class scoped_timed_read_write_lock : private noncopyable
{
public:

    typedef TimedReadWriteMutex mutex_type;

    scoped_timed_read_write_lock(
        TimedReadWriteMutex& mx,
        read_write_lock_state::read_write_lock_state_enum initial_state)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initial_state == read_write_lock_state::read_locked)
            read_lock();
        else if (initial_state == read_write_lock_state::write_locked)
            write_lock();
    }

    ~scoped_timed_read_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void read_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::read_lock(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    bool try_read_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::try_read_lock(m_mutex))
        {
            m_state = read_write_lock_state::read_locked;
            return true;
        }
        return false;
    }

    bool timed_read_lock(const xtime &xt)
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::timed_read_lock(m_mutex,xt))
        {
            m_state = read_write_lock_state::read_locked;
            return true;
        }
        return false;
    }

    void write_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::write_lock(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    bool try_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::try_write_lock(m_mutex))
        {
            m_state = read_write_lock_state::write_locked;
            return true;
        }
        return false;
    }

    bool timed_write_lock(const xtime &xt)
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::timed_write_lock(m_mutex,xt))
        {
            m_state = read_write_lock_state::write_locked;
            return true;
        }
        return false;
    }

    void unlock()
    {
        if (m_state == read_write_lock_state::unlocked) throw lock_error();
        if (m_state == read_write_lock_state::read_locked)
            read_write_lock_ops<TimedReadWriteMutex>::read_unlock(m_mutex);
        else //(m_state == read_write_lock_state::write_locked)
            read_write_lock_ops<TimedReadWriteMutex>::write_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }

    void demote(void)
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::demote(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    bool try_demote(void)
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        return read_write_lock_ops<TimedReadWriteMutex>::try_demote(m_mutex) ? (m_state = read_write_lock_state::read_locked, true) : false;
    }

    bool timed_demote(const xtime &xt)
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        return read_write_lock_ops<TimedReadWriteMutex>::timed_demote(m_mutex, xt) ? (m_state = read_write_lock_state::read_locked, true) : false;
    }

    void promote(void)
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::promote(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    bool try_promote(void)
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        return read_write_lock_ops<TimedReadWriteMutex>::try_promote(m_mutex) ? (m_state = read_write_lock_state::write_locked, true) : false;
    }

    bool timed_promote(const xtime &xt)
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        return read_write_lock_ops<TimedReadWriteMutex>::timed_promote(m_mutex, xt) ? (m_state = read_write_lock_state::write_locked, true) : false;
    }

    //If allow_unlock = true, set_lock always succeedes and
    //the function result indicates whether an unlock was required.
    //If allow_unlock = false, set_lock may fail;
    //the function result indicates whether it succeeded.
    bool set_lock(read_write_lock_state::read_write_lock_state_enum ls, bool allow_unlock = true)
    {
        bool result = !allow_unlock;

        if (m_state != ls)
        {
            if (m_state == read_write_lock_state::unlocked)
            {
                if (ls == read_write_lock_state::read_locked)
                    read_lock();
                else //(ls == read_write_lock_state::write_locked)
                    write_lock();
            }
            else //(m_state == read_write_lock_state::read_locked || m_state == read_write_lock_state::write_locked)
            {
                if (ls == read_write_lock_state::read_locked)
                    demote();
                else if (ls == read_write_lock_state::write_locked)
                {
                    if (!try_promote())
                    {
                        if (allow_unlock)
                        {
                            result = true;
                            unlock();
                            write_lock();
                        }
                        else
                            result = false;
                    }
                }
                else //(ls == read_write_lock_state::unlocked)
                    unlock();
            }
        }

        return result;
    }

    bool try_set_lock(read_write_lock_state::read_write_lock_state_enum ls)
    {
        if (m_state != ls)
        {
            if (m_state == read_write_lock_state::unlocked)
            {
                if (ls == read_write_lock_state::read_locked)
                    return try_read_lock();
                else // (ls == read_write_lock_state::write_locked)
                    return try_write_lock();
            }
            else //(m_state == read_write_lock_state::read_locked || m_state == read_write_lock_state::write_locked)
            {
                if (ls == read_write_lock_state::read_locked)
                    return try_demote();
                else if (ls == read_write_lock_state::write_locked)
                    return try_promote();
                else //(ls == read_write_lock_state::unlocked)
                    return unlock(), true;
            }
        }
        else //(m_state == ls) 
            return true;
    }

    bool timed_set_lock(read_write_lock_state::read_write_lock_state_enum ls, const xtime &xt)
    {
        if (m_state != ls)
        {
            if (m_state == read_write_lock_state::unlocked)
            {
                if (ls == read_write_lock_state::read_locked)
                    return timed_read_lock(xt);
                else // (ls == read_write_lock_state::write_locked)
                    return timed_write_lock(xt);
            }
            else //(m_state == read_write_lock_state::read_locked || m_state == read_write_lock_state::write_locked)
            {
                if (ls == read_write_lock_state::read_locked)
                    return timed_demote(xt);
                else if (ls == read_write_lock_state::write_locked)
                    return timed_promote(xt);
                else //(ls == read_write_lock_state::unlocked)
                    return unlock(), true;
            }
        }
        else //(m_state == ls)
            return true;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }
  
    bool read_locked() const
    {
        return m_state == read_write_lock_state::read_locked;
    }
  
    bool write_locked() const
    {
        return m_state != read_write_lock_state::write_locked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

    read_write_lock_state::read_write_lock_state_enum state() const
    {
        return m_state;
    }

private:

    TimedReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename TimedReadWriteMutex>
class scoped_timed_read_lock : private noncopyable
{
public:

    typedef TimedReadWriteMutex mutex_type;

    explicit scoped_timed_read_lock(
        TimedReadWriteMutex& mx,
        bool initially_locked = true)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initially_locked)
            lock();
    }

    ~scoped_timed_read_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::read_lock(m_mutex);
        m_state = read_write_lock_state::read_locked;
    }

    bool try_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::try_read_lock(m_mutex))
        {
            m_state = read_write_lock_state::read_locked;
            return true;
        }
        return false;
    }

    bool timed_lock(const xtime &xt)
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::timed_read_lock(m_mutex,xt))
        {
            m_state = read_write_lock_state::read_locked;
            return true;
        }
        return false;
    }

    void unlock()
    {
        if (m_state != read_write_lock_state::read_locked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::read_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

    read_write_lock_state::read_write_lock_state_enum state() const
    {
        return m_state;
    }

private:

    TimedReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

template <typename TimedReadWriteMutex>
class scoped_timed_write_lock : private noncopyable
{
public:

    typedef TimedReadWriteMutex mutex_type;

    explicit scoped_timed_write_lock(
        TimedReadWriteMutex& mx,
        bool initially_locked = true)
        : m_mutex(mx), m_state(read_write_lock_state::unlocked)
    {
        if (initially_locked)
            lock();
    }

    ~scoped_timed_write_lock()
    {
        if (m_state != read_write_lock_state::unlocked)
            unlock();
    }

    void lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::write_lock(m_mutex);
        m_state = read_write_lock_state::write_locked;
    }

    bool try_lock()
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::try_write_lock(m_mutex))
        {
            m_state = read_write_lock_state::write_locked;
            return true;
        }
        return false;
    }

    bool timed_lock(const xtime &xt)
    {
        if (m_state != read_write_lock_state::unlocked) throw lock_error();
        if(read_write_lock_ops<TimedReadWriteMutex>::timed_write_lock(m_mutex,xt))
        {
            m_state = read_write_lock_state::write_locked;
            return true;
        }
        return false;
    }

    void unlock()
    {
        if (m_state != read_write_lock_state::write_locked) throw lock_error();
        read_write_lock_ops<TimedReadWriteMutex>::write_unlock(m_mutex);

        m_state = read_write_lock_state::unlocked;
    }
  
    bool locked() const
    {
        return m_state != read_write_lock_state::unlocked;
    }

    operator const void*() const
    {
        return (m_state != read_write_lock_state::unlocked) ? this : 0; 
    }

    read_write_lock_state::read_write_lock_state_enum state() const
    {
        return m_state;
    }

private:

    TimedReadWriteMutex& m_mutex;
    read_write_lock_state::read_write_lock_state_enum m_state;
};

} // namespace thread
} // namespace detail
} // namespace boost

#endif

// Change Log:
//  10 Mar 02 
//      Original version.
//   4 May 04 GlassfordM 
//      Implement lock promotion and demotion (add member functions demote(),
//         try_demote(), timed_demote(), try_promote(), timed_promote(); note 
//         that there is intentionally no promote() member function).
//      Add set_lock() member function.
//      Change try lock & timed lock constructor parameters for consistency.
//      Rename to improve consistency and eliminate abbreviations:
//          Use "read" and "write" instead of "shared" and "exclusive".
//          Change "rd" to "read", "wr" to "write", "rw" to "read_write".
//      Add mutex_type typdef.