Monitor.h

//
// Copyright (c) ZeroC, Inc. All rights reserved.
//

#ifndef ICE_UTIL_MONITOR_H
#define ICE_UTIL_MONITOR_H

#include <IceUtil/Config.h>
#include <IceUtil/Lock.h>
#include <IceUtil/Cond.h>

namespace IceUtil
{

//
// This monitor implements the Mesa monitor semantics. That is any
// calls to notify() or notifyAll() are delayed until the monitor is
// unlocked.
//
template <class T>
class Monitor
{
public:

    typedef LockT<Monitor<T> > Lock;
    typedef TryLockT<Monitor<T> > TryLock;

    Monitor();
    ~Monitor();

    //
    // Note that lock/tryLock & unlock in general should not be used
    // directly. Instead use Lock & TryLock.
    //
    void lock() const;
    void unlock() const;
    bool tryLock() const;

    void wait() const;
    bool timedWait(const Time&) const;
    void notify();
    void notifyAll();

private:

    // noncopyable
    Monitor(const Monitor&);
    void operator=(const Monitor&);

    void notifyImpl(int) const;

    mutable Cond _cond;
    T _mutex;
    mutable int _nnotify;
};

} // End namespace IceUtil

//
// Since this monitor implements the Mesa monitor semantics calls to
// notify() or notifyAll() are delayed until the monitor is
// unlocked. This can happen either due to a call to unlock(), or a
// call to wait(). The _nnotify flag keeps track of the number of
// pending notification calls. -1 indicates a broadcast, a positive
// number indicates <n> calls to notify(). The _nnotify flag is reset
// upon initial acquisition of the monitor lock (either through a call
// to lock(), or a return from wait().
//

template <class T> inline
IceUtil::Monitor<T>::Monitor() :
    _nnotify(0)
{
}

template <class T> inline
IceUtil::Monitor<T>::~Monitor()
{
}

template <class T> inline void
IceUtil::Monitor<T>::lock() const
{
    _mutex.lock();
    if(_mutex.willUnlock())
    {
        //
        // On the first mutex acquisition reset the number pending
        // notifications.
        //
        _nnotify = 0;
    }
}

template <class T> inline void
IceUtil::Monitor<T>::unlock() const
{
    if(_mutex.willUnlock())
    {
        //
        // Perform any pending notifications.
        //
        notifyImpl(_nnotify);
    }
    _mutex.unlock();

/*
    int nnotify = _nnotify;
    if(_mutex.unlock())
    {
        //
        // Perform any pending notifications.
        //
        notifyImpl(nnotify);
    }
*/
}

template <class T> inline bool
IceUtil::Monitor<T>::tryLock() const
{
    bool result = _mutex.tryLock();
    if(result && _mutex.willUnlock())
    {
        //
        // On the first mutex acquisition reset the number pending
        // notifications.
        //
        _nnotify = 0;
    }
    return result;
}

template <class T> inline void
IceUtil::Monitor<T>::wait() const
{
    //
    // Perform any pending notifies
    //
    notifyImpl(_nnotify);

    //
    // Wait for a notification
    //
    try
    {
        _cond.waitImpl(_mutex);
        //
        // Reset the nnotify count once wait() returns.
        //
    }
    catch(...)
    {
        _nnotify = 0;
        throw;
    }

    _nnotify = 0;
}

template <class T> inline bool
IceUtil::Monitor<T>::timedWait(const Time& timeout) const
{
    //
    // Perform any pending notifies.
    //
    notifyImpl(_nnotify);

    bool rc;
    //
    // Wait for a notification.
    //
    try
    {
        rc = _cond.timedWaitImpl(_mutex, timeout);

        //
        // Reset the nnotify count once wait() returns.
        //
    }
    catch(...)
    {
        _nnotify = 0;
        throw;
    }

    _nnotify = 0;
    return rc;
}

template <class T> inline void
IceUtil::Monitor<T>::notify()
{
    //
    // Increment the _nnotify flag, unless a broadcast has already
    // been requested.
    //
    if(_nnotify != -1)
    {
        ++_nnotify;
    }
}

template <class T> inline void
IceUtil::Monitor<T>::notifyAll()
{
    //
    // -1 (indicates broadcast)
    //
    _nnotify = -1;
}

template <class T> inline void
IceUtil::Monitor<T>::notifyImpl(int nnotify) const
{
    //
    // Zero indicates no notifies.
    //
    if(nnotify != 0)
    {
        //
        // -1 means notifyAll.
        //
        if(nnotify == -1)
        {
            _cond.broadcast();
            return;
        }
        else
        {
            //
            // Otherwise notify n times.
            //
            while(nnotify > 0)
            {
                _cond.signal();
                --nnotify;
            }
        }
    }
}

#endif