FutureValue.h

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/*
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   The MIT License

   Copyright (c) 2009 Scientific Computing and Imaging Institute,
   University of Utah.

   
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///
///@file   FutureValue.h
///@brief  Delayed return values
///
///@author Steve Parker
///        Department of Computer Science
///        University of Utah
///@date   June 1997
///

#ifndef Core_Thread_FutureValue_h
#define Core_Thread_FutureValue_h

#include <Core/Thread/Legacy/Legacy/Semaphore.h>
#include <Core/Thread/Legacy/Legacy/Thread.h>

namespace SCIRun {
/**************************************
 
@class
  FutureValue
   
  KEYWORDS
  Thread
   
@details
  Creates a single slot for some return value.  The <i>wait</i> method
  waits for a value to be sent from another thread via the <i>reply</i>
  method.  This is typically used to provide a simple means of returning
  data from a server thread.  An <b>FutureValue</b> object is created on the
  stack, and some request is sent (usually via a <b>Mailbox</b>) to a server
  thread.  Then the thread will block in <i>wait</i> until the server thread
  receives the message and responds using <i>reply</i>.
  
  <p><b>FutureValue</b> is a one-shot wait/reply pair - a new
  <b>FutureValue</b> object must be created for each reply, and these are
  typically created on the stack.  Only a single thread should
  call <i>wait</i> and a single thread shuold call <i>reply</i>.
  
****************************************/
template<class Item> class FutureValue {
public:
  //////////
  /// Create the FutureValue object.  <i>name</i> should be a
  /// static string which describes the primitive for debugging
  /// purposes.
  FutureValue(const char* name);

  //////////
  /// Destroy the object
  ~FutureValue();

  //////////
  /// Wait until the reply is sent by anothe thread, then return
  /// that reply.
  Item receive();

  //////////
  /// Send the reply to the waiting thread.
  void send(const Item& reply);

private:
  const char* name;
  Item value;
  Semaphore sema;

  // Cannot copy them
  FutureValue(const FutureValue<Item>&);
  FutureValue<Item>& operator=(const FutureValue<Item>&);
};

template<class Item>
FutureValue<Item>::FutureValue(const char* name)
    : name(name), sema("FutureValue semaphore", 0)
{
}

template<class Item>
FutureValue<Item>::~FutureValue()
{
}

template<class Item>
Item
FutureValue<Item>::receive()
{
  int s=Thread::couldBlock(name);
  sema.down();
  Thread::couldBlockDone(s);
  return value;
} // End namespace SCIRun

template<class Item>
void
FutureValue<Item>::send(const Item& reply)
{
  value=reply;
  sema.up();
}
} // End namespace SCIRun

#endif