/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

/*

 * Copyright (c) 2008 University of Washington

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation;

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

#ifndef SYSTEM_CONDITION_H

#define SYSTEM_CONDITION_H

#include "ptr.h"

class SystemConditionPrivate;

/**

 * @brief A class which provides a relatively platform-independent 

 * conditional-wait thread synchronization primitive.

 *

 * It is often desirable to have a mechanism by which a thread can suspend its

 * execution and relinquish the process until some condition to becomes true.

 * We provide platform-independent access to this OS-dependent capability with

 * the SystemCondition class.

 *

 * There are two ways to tell the underlying primitive that the condition has

 * become true:  Signal and Broadcast.  Signal will only wake up one thread

 * waiting on the condition (according to the OS scheduling policy); 

 * Broadcast will wake up all of the threads waiting on the condition 

 * (cf. "The Thundering Herd").

 * 

 * In order to wait for the underlying condition, you also have two

 * alternatives:  Wait and TimedWait.  The Wait call will wait forever for the

 * condition to become true; but the TimedWait has a timeout.

 *

 * The condition underlying this class is a simple boolean variable.  It is

 * set to false in each call to Wait and TimedWait.  It is set to true in each

 * call to Signal and Broadcast.  This is a fairly simple-minded condition

 * designed for 

 *

 * A typical use case will be to call Wait() or TimedWait() in one thread

 * context and put the processor to sleep until an event happens somewhere 

 * else that 

 */

class SystemCondition

{

public:

  SystemCondition ();

  ~SystemCondition ();

  /**

   * Set the value of the underlying condition.

   */

  void SetCondition (bool condition);

  /**

   * Get the value of the underlying condition.

   */

  bool GetCondition (void);

  /**

   * Release one thread if waiting for the condition to be true.  If you want 

   * a waiting thread to return, you should have done a SetCondition (true)

   * prior to calling.

   */

  void Signal (void);

  /**

   * Release all threads waiting for the condition to be true.  If you want 

   * all waiting threads to return, you should have done a SetCondition (true)

   * prior to calling.

   */

  void Broadcast (void);

  /**

   * Wait, possibly forever, for the condition to be true.

   */

  void Wait (void);

  /**

   * Wait a maximum of ns nanoseconds for the condition to be true.  If the

   * wait times out, return true else return false.

   */

  bool TimedWait (uint64_t ns);

private:

  SystemConditionPrivate * m_priv;

};

} // namespace ns3

#endif /* SYSTEM_CONDITION_H */