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/* EventQueue.java -- Event queuing mechanism
Copyright (C) 1999 Free Software Foundation, Inc.
This file is part of the non-peer AWT libraries of GNU Classpath.
This library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published
by the Free Software Foundation, either version 2 of the License, or
(at your option) any later verion.
This library 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 Library General Public License for more details.
You should have received a copy of the GNU Library General Public License
along with this library; if not, write to the Free Software Foundation
Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307 USA. */
package java.awt;
/**
* This class manages a queue of <code>AWTEvent</code> objects that
* are posted to it. The AWT system uses only one event queue for all
* events.
*
* @author Aaron M. Renn (arenn@urbanophile.com)
*/
public class EventQueue
{
/*
* Instance Methods
*/
// The queue. We added a package protected field to AWTEvent to make it
// a convenient linked list.
private AWTEvent queue;
/*************************************************************************/
/*
* Constructors
*/
/**
* Initializes a new instance of <code>EventQueue</code>.
*/
public
EventQueue()
{
EventDispatcher ed = new EventDispatcher(this);
Thread t = new Thread(ed);
t.start();
}
/*************************************************************************/
/*
* Instance Variables
*/
/**
* Posts a new event to the queue.
*
* @param event The event to post to the queue.
*/
public synchronized void
postEvent(AWTEvent event)
{
if (queue == null)
queue = event;
else
{
AWTEvent end = queue;
while (end.next != null)
end = end.next;
end.next = queue;
}
notify();
}
/*************************************************************************/
/**
* Returns the next event in the queue. This method will block until
* an event is available or until the thread is interrupted.
*
* @return The next event in the queue.
*
* @exception InterruptedException If this thread is interrupted while
* waiting for an event to be posted to the queue.
*/
public synchronized AWTEvent
getNextEvent() throws InterruptedException
{
for (;;)
{
if (queue != null)
{
AWTEvent evt = queue;
queue = queue.next;
evt.next = null;
return(evt);
}
wait();
}
}
/*************************************************************************/
/**
* Returns the next event in the queue without removing it from the queue.
* This method will block until an event is available or until the thread
* is interrupted.
*
* @return The next event in the queue.
*/
public synchronized AWTEvent
peekEvent()
{
for (;;)
{
if (queue != null)
{
// We are taking a chance that the user doesn't repost the same
// event back to the queue, but AWTEvent isn't cloneable so we
// don't have much choice. If this becomes a problem we'll have
// to write a wrapper class for enqueuing.
return(queue);
}
try
{
wait();
}
catch(InterruptedException e) { }
}
}
/*************************************************************************/
/**
* Returns the next event in the queue that has the specified id
* without removing it from the queue.
* This method will block until an event is available or until the thread
* is interrupted.
*
* @param id The event id to return.
*
* @return The next event in the queue.
*/
public synchronized AWTEvent
peekEvent(int id)
{
for(;;)
{
if (queue != null)
{
AWTEvent evt = queue;
while (evt != null)
{
if (evt.getID() == id)
return(evt);
evt = evt.next;
}
}
try
{
wait();
}
catch(InterruptedException e) { }
}
}
} // class EventQueue
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