--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/core/system-condition.h	Tue Jul 15 15:59:57 2008 -0700
@@ -0,0 +1,106 @@
+/* -*- 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"
+
+namespace ns3 { 
+	
+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 */
+
+