Class that provides an interface to timers.

1 files changed, 379 insertions, 0 deletions

diff --git a/java/src/TimerQueue.java b/java/src/TimerQueue.java
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+/*************************************************
+ *
+ * = PACKAGE
+ *    ACE.Reactor
+ *
+ * = FILENAME
+ *    TimerQueue.java
+ *
+ *@author Prashant Jain
+ *
+ *************************************************/
+package ACE.Reactor;
+
+import java.util.*;
+import ACE.ASX.*;
+
+class TimerNode
+{
+  public TimerNode (EventHandler handler,
+		    Object arg,
+		    TimeValue timerValue,
+		    TimeValue interval,
+		    TimerNode next,
+		    int timerId)
+  {
+    this.handler_ = handler;
+    this.arg_ = arg;
+    this.timerValue_ = timerValue;
+    this.interval_ = interval;
+    this.next_ = next;
+    this.timerId_ = timerId;
+  }
+
+  public EventHandler handler_;
+  // Handler to invoke <handleTimeout> on when a timeout occurs.
+
+  public Object arg_;
+  // Argument to pass to <handleTimeout>.
+
+  public TimeValue timerValue_;
+  // Time until the timer expires.
+
+  public TimeValue interval_;
+  // If this is a periodic timer this holds the time until the next
+  // timeout.
+
+  public TimerNode next_;
+  // Pointer to next timer.
+  
+  public int timerId_;
+  // Id of this timer (used to cancel timers before they expire).
+}
+
+class WaitObject extends TimedWait
+{
+  public boolean condition ()
+  {
+    return this.condition_;
+  }
+  
+  public void condition (boolean c)
+  {
+    this.condition_ = c;
+  }
+
+  private boolean condition_ = false;
+}
+
+/**
+ * <hr>
+ * <h2>SYNOPSIS</h2>
+ *<blockquote>
+ *     Class that provides an interface to timers. 
+ *
+ *</blockquote>
+ *
+ * <h2>DESCRIPTION</h2>
+ *<blockquote>
+ *     This is a simple implementation that keeps a linked list of
+ *     absolute timers. It allows multiple timers to be scheduled
+ *     and returns a timer id for each timer scheduled. In addition,
+ *     it allows periodic timers to be scheduled.
+ *</blockquote>
+ */
+public class TimerQueue implements Runnable
+{
+  /**
+   * Default Constructor
+   */
+  public TimerQueue ()
+  {
+    new Thread (this).start ();
+  }
+
+  /**
+   * This is the work horse of TimerQueue. It forms the event loop and
+   * takes care of all scheduling.
+   */
+  public void run ()
+  {
+    TimeValue timeout = null;
+    TimeValue earliest = null;
+
+    for (;;)
+      {
+	synchronized (this.obj_) 
+	  {
+	    earliest = this.earliestTime ();
+	    if (earliest != null)
+	      timeout = TimeValue.minus (earliest, TimeValue.getTimeOfDay ());
+	    else
+	      timeout = new TimeValue ();
+	    try
+	      {
+		//		System.out.println (timeout);
+		// Extract the earliest time from the queue and do a timed wait
+		this.obj_.timedWait (timeout);
+		
+		// We have been notified. Check to see if we need to
+		// restart the wait with a different timeout
+		if (this.reset_)
+		  {
+		    this.reset_ = false;
+		    this.obj_.condition (false);
+		    timeout = TimeValue.minus (this.earliestTime (), TimeValue.getTimeOfDay ());
+		  }
+	      }
+	    catch (TimeoutException e)
+	      {
+		// Timeout occurred. Call handleTimeout on appropriate
+		// Event Handlers
+		this.dispatchHandlers ();
+	      }
+	    catch (InterruptedException e)
+	      {
+	      }
+	  }
+      }
+  }
+
+  /**
+   * Check if the queue is empty.
+   *@return true if queue is empty, else false.
+   */
+  boolean isEmpty ()
+  {
+    return this.head_ == null;
+  }
+
+  /**
+   * Get the node of the earliest node in the TimerQueue.
+   *@return the time of the earlier node in the TimerQueue.
+   */
+  TimeValue earliestTime ()
+  {
+    synchronized (this.obj_)
+      {
+	if (!this.isEmpty ())
+	  return this.head_.timerValue_;
+	else
+	  return null;
+      }
+  }
+
+  /**
+   * Schedule an <EventHandler> that will expire after <delta> amount
+   * of time.  If it expires then <obj> is passed in as the value to
+   * the <EventHandler>'s <handleTimeout> callback method. This method
+   * returns a timer id that uniquely identifies the timer and can be
+   * used to cancel the timer before it expires.
+   *@param handler Event Handler that is to be scheduled with the timer
+   *@param obj Object that is passed back to the Event Handler when
+   * timeout occurs (Asynchronous Completion Token)
+   *@param delta amount of time for which to schedule the timer
+   *@return id of the timer scheduled
+   */
+  public int scheduleTimer (EventHandler handler,
+			     Object obj,
+			     TimeValue delta)
+  {
+    return this.scheduleTimer (handler, obj, delta, TimeValue.zero);
+  }
+
+  /**
+   * Schedule an <EventHandler> that will expire after <delta> amount
+   * of time.  If it expires then <obj> is passed in as the value to
+   * the <EventHandler>'s <handleTimeout> callback method.  If
+   * <interval> is != to <TimeValue.zero> then it is used to
+   * reschedule the <EventHandler> automatically.  This method
+   * returns a timer id that uniquely identifies the timer and can be
+   * used to cancel the timer before it expires.
+   *@param handler Event Handler that is to be scheduled with the timer
+   *@param arg Object that is passed back to the Event Handler when
+   * timeout occurs (Asynchronous Completion Token)
+   *@param timeout amount of time for which to schedule the timer
+   *@param interval amount of time to use to reschedule the timer
+   *@return id of the timer scheduled
+   */
+  public int scheduleTimer (EventHandler handler,
+			    Object arg,
+			    TimeValue timeout,
+			    TimeValue interval)
+  {
+    // Increment the sequence number (it will wrap around).
+    this.timerId_++;
+    TimeValue futureTime = TimeValue.plus (timeout, TimeValue.getTimeOfDay ());
+    TimerNode node = new TimerNode (handler, 
+				    arg,
+				    futureTime,
+				    interval, 
+				    null,
+				    this.timerId_);
+    synchronized (this.obj_)
+      {
+	if (this.isEmpty () || futureTime.lessThan (this.earliestTime ()))
+	  {
+	    // Place at the beginning of the list.
+	    this.reschedule (node);
+	    this.obj_.condition (true);
+	    this.reset_ = true;
+
+	    // Notify the waiting thread so that it can reschedule
+	    // using the earliest timeout
+	    this.obj_.notify ();
+	  }
+	else // Place in the middle of the list somewhere.
+	  {
+	    this.reschedule (node);
+	  }
+      }
+    return this.timerId_;
+  }
+
+
+  /**
+   * Cancel the single timer associated with <timerId>.
+   *@param timerId id of the timer that needs to be cancelled.
+   *@return Object that was passed in when timer was scheduled
+   * (Asynchronous Completion Token). 
+   */
+  public Object cancelTimer (int timerId)
+  {
+    TimerNode prev = null;
+    TimerNode curr = null;
+
+    // Try to locate the TimerNode that matches the timerId.
+
+    for (curr = this.head_; 
+	 curr != null && curr.timerId_ != timerId;
+	 curr = curr.next_)
+      prev = curr;
+
+    if (curr != null)
+      {
+	if (prev == null)
+	  this.head_ = curr.next_;
+	else
+	  prev.next_ = curr.next_;
+
+	return curr.arg_;
+      }
+    return null;
+  }
+
+  /**
+   * Cancel all timers associated with <Event Handler>.
+   *@param handler Event Handler whose associated timers need to be cancelled.
+   */
+  public void cancelTimer (EventHandler handler)
+  {
+    TimerNode prev = null;
+    TimerNode curr = this.head_;
+
+    while (curr != null)
+      {
+	if (curr.handler_ == handler)
+	  {
+	    if (prev == null)
+	      {
+		this.head_ = curr.next_;
+		curr = this.head_;
+	      }
+	    else
+	      {
+		prev.next_ = curr.next_;
+		curr = prev.next_;
+	      }
+	  }
+	else
+	  {
+	    prev = curr;
+	    curr = curr.next_;
+	  }
+      }
+  }
+
+  // Call handleTimeout() on all handlers whose timers have expired.
+  private void dispatchHandlers ()
+  {
+    TimeValue currentTime = TimeValue.getTimeOfDay ();
+
+    for (;;)
+      {
+	if (this.isEmpty () || this.earliestTime ().greaterThan (currentTime))
+	  break; // There aren't any more timers eligible to expire.
+
+	TimerNode expired = this.head_;
+	EventHandler handler = expired.handler_;
+	Object arg = expired.arg_;
+	int result;
+	
+	this.head_ = this.head_.next_;
+	
+	// Check whether this is an interval timer.
+	if (expired.interval_.greaterThan (TimeValue.zero))
+	  {
+	    // Make sure that we skip past values that have already
+	    // "expired".
+	    do
+	      expired.timerValue_.plusEquals (expired.interval_);
+	    while (expired.timerValue_.lessThanEqual (currentTime));
+		   
+	    // Since this is an interval timer, we need to reschedule
+	    // it.
+	    this.reschedule (expired);
+	  }
+	
+	// Perform the callback.
+	result = handler.handleTimeout (currentTime, arg);
+	
+	if (result == -1)
+	  this.cancelTimer (handler);
+      }
+  }
+
+  // Reschedule a TimerNode by inserting it at the appropriate
+  // position in the queue.
+  private void reschedule (TimerNode expired)
+  {
+    if (this.isEmpty () || 
+	expired.timerValue_.lessThan (this.earliestTime ()))
+      {
+	expired.next_ = this.head_;
+	this.head_ = expired;
+      }
+    else
+      {
+	TimerNode prev = this.head_;
+	TimerNode after  = this.head_.next_;
+
+	// Locate the proper position in the queue. 
+
+	while (after != null 
+	       && expired.timerValue_.greaterThan (after.timerValue_))
+	  {
+	    prev = after;
+	    after  = after.next_;
+	  }
+
+	expired.next_ = after;
+	prev.next_  = expired;
+      }
+  }
+
+  private WaitObject obj_ = new WaitObject ();
+  // Synchronization object (as well as object to use to do wait on)
+
+  private TimerNode head_; 
+  // Pointer to linked list of TimerHandles. 
+
+  private int timerId_;
+  // Keeps track of the timer id that uniquely identifies each timer.
+  // This id can be used to cancel a timer via the <cancel (int)>
+  // method.
+
+  private boolean reset_;
+  // Flag indicating whether to start the wait again
+}
+