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Monitor.h

// **********************************************************************
//
// Copyright (c) 2003-2005 ZeroC, Inc. All rights reserved.
//
// This copy of Ice is licensed to you under the terms described in the
// ICE_LICENSE file included in this distribution.
//
// **********************************************************************

#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

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