/* -*- C++ -*- */
// $Id$

// ============================================================================
//
// = LIBRARY
//    ace
// 
// = FILENAME
//    Future.h
//
// = AUTHOR
//    Andres Kruse <Andres.Kruse@cern.ch>, Douglas C. Schmidt
//    <schmidt@cs.wustl.edu>, and Per Andersson
//    <Per.Andersson@hfera.ericsson.se>. 
// 
// ============================================================================

#ifndef ACE_FUTURE_H
#define ACE_FUTURE_H

#include "ace/Synch.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
#pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#if defined (ACE_HAS_THREADS)

// Forward decl.
template <class T> class ACE_Future;

template <class T>
class ACE_Future_Rep
{
  // = TITLE
  //     ACE_Future_Rep<T>
  //
  // = DESCRIPTION
  //     An ACE_Future_Rep<T> object encapsules a pointer to an 
  //     object of class T which is the result of an asynchronous
  //     method invocation. It is pointed to by ACE_Future<T> object[s]
  //     and only accessible through them.
private:
  friend class ACE_Future<T>;
  
  // Create, attach, detach and assign encapsulates the reference
  // count handling and the object lifetime of ACE_Future_Rep<T>
  // instances.
  
  static ACE_Future_Rep<T> *create (void);
  // Create a ACE_Future_Rep<T> and initialize the reference count
  
  static ACE_Future_Rep<T> *attach (ACE_Future_Rep<T> *&rep);
  // Precondition(rep != 0)
  // Increase the reference count and return argument. Uses
  // the attribute "value_ready_mutex_" to synchronize reference
  // count updating
  
  static void detach (ACE_Future_Rep<T> *&rep);
  // Precondition(rep != 0)
  // Decreases the reference count and and deletes rep if
  // there are no more references to rep.
  
  static void assign (ACE_Future_Rep<T> *&rep,
		      ACE_Future_Rep<T> *new_rep);
  // Precondition(rep != 0 && new_rep != 0)
  // Decreases the rep's reference count and and deletes rep if there
  // are no more references to rep. Then assigns new_rep to rep
  
  int set (const T &r);
  // Set the result value.

  int get (T &value,
	   ACE_Time_Value *tv);
  // Wait up to <tv> time to get the <value>.

  operator T ();
  // Type conversion. will block forever until the result is
  // available.  Note that this method is going away in a subsequent
  // release since it doesn't distinguish between failure results and
  // success results (exceptions should be used, but they aren't
  // portable...).  The <get> method should be used instead since it
  // separates the error value from the result, and also permits
  // timeouts.

  void dump (void) const;
  // Dump the state of an object.

  ACE_ALLOC_HOOK_DECLARE;
  // Declare the dynamic allocation hooks.

  // = Constructor and destructor private
  ACE_Future_Rep (void);
  ~ACE_Future_Rep (void);

  int ready (void);
  // Is result available?

  T *value_;
  // Pointer to the result.

  int ref_count_;
  // Reference count.

  // = Condition variable and mutex that protect the <value_>.
  ACE_Condition_Thread_Mutex value_ready_;
  ACE_Thread_Mutex value_ready_mutex_;
};

template <class T>
class ACE_Future 
{
  // = TITLE
  //     This class implements a ``single write, multiple read''
  //     pattern that can be used to return results from asynchronous
  //     method invocations.
public:
  // = Initialization and termination methods.
  ACE_Future (void);
  // Constructor.

  ACE_Future (const ACE_Future<T> &r);
  // Copy constructor binds <this> and <r> to the same
  // <ACE_Future_Rep>. An <ACE_Future_Rep> is created if necessary.

  ACE_Future (const T &r);
  // Constructor that initialises an <ACE_Future> to point to the
  // result <r> immediately.

  ~ACE_Future (void);
  // Destructor.

  void operator = (const ACE_Future<T> &r);
  // Assignment operator that binds <this> and <r> to the same
  // <ACE_Future_Rep>. An <ACE_Future_Rep> is created if necessary.

  int cancel (const T &r);
  // Cancel an <ACE_Future> and assign the value <r>.  It is used if a
  // client does not want to wait for <T> to be produced.
  
  int cancel (void);
  // Cancel an <ACE_Future>.  Put the future into its initial
  // state. Returns 0 on succes and -1 on failure. It is now possible
  // to reuse the ACE_Future<T>. But remember, the ACE_Future<T>
  // is now bound to a new ACE_Future_Rep<T>.

  int operator == (const ACE_Future<T> &r) const;
  // Equality operator that returns 1 if both ACE_Future<T> objects
  // point to the same ACE_Future_Rep<T> object.  Attention: It also
  // returns 1 if both objects have just been instantiated and not
  // used yet.

  int operator != (const ACE_Future<T> &r) const;
  // Inequality operator, which is the opposite of equality.

  int set (const T &r);
  // Make the result available. Is used by the server thread to give
  // the result to all waiting clients.

  int get (T &value,
	   ACE_Time_Value *tv = 0);
  // Wait up to <tv> time to get the <value>.

  operator T ();
  // Type conversion, which obtains the result of the asynchronous
  // method invocation.  Will block forever.  Note that this method is
  // going away in a subsequent release since it doesn't distinguish
  // between failure results and success results (exceptions should be
  // used, but they aren't portable...).  The <get> method should be
  // used instead since it separates the error value from the result,
  // and also permits timeouts.

  int ready (void);
  // Check if the result is available.

  void dump (void) const;
  // Dump the state of an object.

  ACE_ALLOC_HOOK_DECLARE;
  // Declare the dynamic allocation hooks.

private:
  void *operator new (size_t nbytes);
  // Do not allow new operator.

  void operator delete (void *);
  // Do not allow delete operator

  void operator &();
  // Do not allow address-of operator.

  // the ACE_Future_Rep
  typedef ACE_Future_Rep<T> FUTURE_REP;
  FUTURE_REP *future_rep_;
  // Protect operations on the <Future>.
};

#if defined (ACE_TEMPLATES_REQUIRE_SOURCE)
#include "ace/Future.cpp"
#endif /* ACE_TEMPLATES_REQUIRE_SOURCE */

#if defined (ACE_TEMPLATES_REQUIRE_PRAGMA)
#pragma implementation ("Future.cpp")
#endif /* ACE_TEMPLATES_REQUIRE_PRAGMA */

#endif /* ACE_HAS_THREADS */
#endif /* ACE_FUTURE_H */