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Condition.h

//
// Condition.h
//
// $Id: //poco/1.4/Foundation/include/Poco/Condition.h#1 $
//
// Library: Foundation
// Package: Threading
// Module:  Condition
//
// Definition of the Condition class template.
//
// Copyright (c) 2007, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_Condition_INCLUDED
#define Foundation_Condition_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/Mutex.h"
#include "Poco/ScopedUnlock.h"
#include "Poco/Event.h"
#include "Poco/Exception.h"
#include <deque>


namespace Poco {


00054 class Foundation_API Condition
      /// A Condition is a synchronization object used to block a thread 
      /// until a particular condition is met. 
      /// A Condition object is always used in conjunction with
      /// a Mutex (or FastMutex) object.
      ///
      /// Condition objects are similar to POSIX condition variables, which the
      /// difference that Condition is not subject to spurious wakeups.
      ///
      /// Threads waiting on a Condition are resumed in FIFO order.
{
public:
      Condition();
            /// Creates the Condition.
      
      ~Condition();
            /// Destroys the Condition.
      
      template <class Mtx>
00073       void wait(Mtx& mutex)
            /// Unlocks the mutex (which must be locked upon calling
            /// wait()) and waits until the Condition is signalled.
            ///
            /// The given mutex will be locked again upon 
            /// leaving the function, even in case of an exception.
      {
            ScopedUnlock<Mtx> unlock(mutex, false);
            Event event;
            {
                  FastMutex::ScopedLock lock(_mutex);
                  mutex.unlock();
                  enqueue(event);
            }
            event.wait();
      }
      
      template <class Mtx>
00091       void wait(Mtx& mutex, long milliseconds)
            /// Unlocks the mutex (which must be locked upon calling
            /// wait()) and waits for the given time until the Condition is signalled.
            ///
            /// The given mutex will be locked again upon successfully leaving the 
            /// function, even in case of an exception.
            ///
            /// Throws a TimeoutException if the Condition is not signalled
            /// within the given time interval.
      {
            if (!tryWait(mutex, milliseconds))
                  throw TimeoutException();
      }
      
      template <class Mtx>
00106       bool tryWait(Mtx& mutex, long milliseconds)
            /// Unlocks the mutex (which must be locked upon calling
            /// tryWait()) and waits for the given time until the Condition is signalled.
            ///
            /// The given mutex will be locked again upon leaving the 
            /// function, even in case of an exception.
            ///
            /// Returns true if the Condition has been signalled
            /// within the given time interval, otherwise false.
      {
            ScopedUnlock<Mtx> unlock(mutex, false);
            Event event;
            {
                  FastMutex::ScopedLock lock(_mutex);
                  mutex.unlock();
                  enqueue(event);
            }
            if (!event.tryWait(milliseconds))
            {
                  FastMutex::ScopedLock lock(_mutex);
                  dequeue(event);
                  return false;
            }
            return true;
      }
      
      void signal();
            /// Signals the Condition and allows one waiting thread
            /// to continue execution.

      void broadcast();
            /// Signals the Condition and allows all waiting
            /// threads to continue their execution.

protected:
      void enqueue(Event& event);
      void dequeue();
      void dequeue(Event& event);
      
private:
      Condition(const Condition&);
      Condition& operator = (const Condition&);
      
      typedef std::deque<Event*> WaitQueue;
      
      FastMutex _mutex;
      WaitQueue _waitQueue;
};


} // namespace Poco


#endif // Foundation_Condition_INCLUDED

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