read_write_lock.hpp

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// 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();
    }