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

/*

 * Copyright (c) 2008 INRIA

 *

 * 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

 *

 * Author: Mathieu Lacage <mathieu.lacage.inria.fr>

 */

#ifndef SYSTEM_THREAD_H

#define SYSTEM_THREAD_H

#include "callback.h"

namespace ns3 { 

class SystemThreadImpl;

/**

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

 * primitive.

 *

 * This class allows for creation of multiple threads of execution in a

 * process.  The exact implementation of the thread functionality is 

 * operating system dependent, but typically in ns-3 one is using an 

 * environment in which Posix Threads are supported (either navively or

 * in the case of Windows via Cygwin's implementation of pthreads on the 

 * Win32 API.  In either case we expect that these will be kernel-level

 * threads and therefore a system with multiple CPUs will see truly concurrent 

 * execution.

 *

 * Synchronization between threads is provided via the SystemMutex class.

 */

class SystemThread : public SimpleRefCount<SystemThread>

{

public:

  /**

   * @brief Create a SystemThread object.

   *

   * A system thread object is not created running.  A thread of execution

   * must be explicitly started by calling the Start method.  When the 

   * Start method is called, it will spawn a thread of execution and cause

   * that thread to call out into the callback function provided here as

   * a parameter.

   *

   * Like all ns-3 callbacks, the provided callback may refer to a function

   * or a method of an object depending on how the MakeCallback function is

   * used.

   *

   * The most common use is expected to be creating a thread of execution in

   * a method.  In this case you would use code similar to,

   *

   *   MyClass myObject;

   *   Ptr<SystemThread> st = Create<SystemThread> (

   *     MakeCallback (&MyClass::MyMethod, &myObject));

   *   st->Start ();

   *

   * The SystemThread is passed a callback that calls out to the function

   * MyClass::MyMethod.  When this function is called, it is called as an

   * object method on the myObject object.  Essentially what you are doing

   * is asking the SystemThread to call object->MyMethod () in a new thread

   * of execution.

   *

   * If starting a thread in your currently executing object, you can use the

   * "this" pointer:

   *

   *   Ptr<SystemThread> st = Create<SystemThread> (

   *     MakeCallback (&MyClass::MyMethod, this));

   *   st->Start ();

   *

   * Object lifetime is always an issue with threads, so it is common to use

   * smart pointers.  If you are spinning up a thread in an object that is 

   * managed by a smart pointer, you can use that pointer directly:

   *

   *   Ptr<MyClass> myPtr = Create<MyClass> ();

   *   Ptr<SystemThread> st = Create<SystemThread> (

   *     MakeCallback (&MyClass::MyMethod, myPtr));

   *   st->Start ();

   *

   * Just like any thread, you can synchronize with its termination.  The 

   * method provided to do this is Join (). If you call Join() you will block

   * until the SystemThread run method returns.

   *

   * @param callback entry point of the thread

   * 

   * @warning The SystemThread uses SIGALRM to wake threads that are possibly

   * blocked on IO.

   * @see Shutdown

   *

   * @warning I've made the system thread class look like a normal ns3 object

   * with smart pointers, and living in the heap.  This makes it very easy to

   * manage threads from a single master thread context.  You should be very

   * aware though that I have not made Ptr multithread safe!  This means that

   * if you pass Ptr<SystemThread> around in a multithreaded environment, it is

   * possible that the reference count will get messed up since it is not an

   * atomic operation.  CREATE AND MANAGE YOUR THREADS IN ONE PLACE -- LEAVE

   * THE PTR THERE.

   */

  SystemThread(Callback<void> callback);

  /**

   * @brief Destroy a SystemThread object.

   *

   */

  ~SystemThread();

  /**

   * @brief Start a thread of execution, running the provided callback.

   */

  void Start (void);

  /**

   * @brief Suspend the caller until the thread of execution, running the 

   * provided callback, finishes.

   */

  void Join (void);

  /**

   * @brief Indicates to a managed thread doing cooperative multithreading that

   * its managing thread wants it to exit.

   *

   * It is often the case that we want a thread to be off doing work until such

   * time as its job is done (typically when the simulation is done).  We then 

   * want the thread to exit itself.  This method provides a consistent way for

   * the managing thread to communicate with the managed thread.  After the

   * manager thread calls this method, the Break() method will begin returning

   * true, telling the managed thread to exit.

   *

   * This alone isn't really enough to merit these events, but in Unix, if a

   * worker thread is doing blocking IO, it will need to be woken up from that

   * read somehow.  This method also provides that functionality, by sending a

   * SIGALRM signal to the possibly blocked thread.

   *

   * @warning Uses SIGALRM to notify threads possibly blocked on IO.  Beware

   * if you are using signals.

   * @see Break

   */

  void Shutdown (void);

  /**

   * @brief Indicates to a thread doing cooperative multithreading that

   * its managing thread wants it to exit.

   *

   * It is often the case that we want a thread to be off doing work until such

   * time as its job is done.  We then want the thread to exit itself.  This

   * method allows a thread to query whether or not it should be running.

   * Typically, the worker thread is running in a forever-loop, and will need to

   * "break" out of that loop to exit -- thus the name.

   *

   * @see Shutdown

   * @returns true if thread is expected to exit (break out of the forever-loop)

   */

  bool Break (void);

private:

  SystemThreadImpl * m_impl;

  bool m_break;

};

#endif /* SYSTEM_THREAD_H */