Semaphore.h

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/*
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   Copyright (c) 2009 Scientific Computing and Imaging Institute,
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///
///@file   Semaphore
///@breif  Basic semaphore primitive
///
///@author Steve Parker
///        Department of Computer Science
///        University of Utah
///@date   June 1997
///

#ifndef Core_Thread_Semaphore_h
#define Core_Thread_Semaphore_h

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

namespace SCIRun {

class Semaphore_private;

/**************************************
 
@class
 Semaphore

 KEYWORDS
 Thread

@detials
 Counting semaphore synchronization primitive.  A semaphore provides
 atomic access to a special counter.  The <i>up</i> method is used
 to increment the counter, and the <i>down</i> method is used to
 decrement the counter.  If a thread tries to decrement the counter
 when the counter is zero, that thread will be blocked until another
 thread calls the <i>up</i> method.

****************************************/
class SCISHARE Semaphore {
public:
  //////////
  /// Create the semaphore, and setup the initial <i>count.name</i>
  /// should be a static string which describes the primitive for
  /// debugging purposes.
  Semaphore(const char* name, int count);

  //////////
  /// Destroy the semaphore
  ~Semaphore();

  //////////
  /// Increment the semaphore count, unblocking up to <i>count</i>
  /// threads that may be blocked in the <i>down</i> method.
  void up(int count=1);
    
  //////////
  /// Decrement the semaphore count by <i>count</i>.  If the
  /// count is zero, this thread will be blocked until another
  /// thread calls the <i>up</i> method. The order in which
  /// threads will be unblocked is not defined, but implementors
  /// should give preference to those threads that have waited
  /// the longest.
  void down(int count=1);

  //////////
  /// Attempt to decrement the semaphore count by one, but will
  /// never block. If the count was zero, <i>tryDown</i> will
  /// return false. Otherwise, <i>tryDown</i> will return true.
  bool tryDown();

private:
  Semaphore_private* priv_;
  const char* name_;

  // Cannot copy them
  Semaphore(const Semaphore&);
  Semaphore& operator=(const Semaphore&);
};
} // End namespace SCIRun

#endif