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SWT is an open source widget toolkit for Java designed to provide efficient, portable access to the user-interface facilities of the operating systems on which it is implemented.
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/*******************************************************************************
 * Copyright (c) 2000, 2011 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.widgets;


import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.internal.Compatibility;
 
/**
 * Instances of this class provide synchronization support
 * for displays. A default instance is created automatically
 * for each display, and this instance is sufficient for almost
 * all applications.
 * 
 * IMPORTANT: Typical application code never
 * needs to deal with this class. It is provided only to
 * allow applications which require non-standard
 * synchronization behavior to plug in the support they
 * require. Subclasses which override the methods in 
 * this class must ensure that the superclass methods are
 * invoked in their implementations
 * 
 *
 * @see Display#setSynchronizer
 * @see Sample code and further information
 */
public class Synchronizer {
	Display display;
	int messageCount;
	RunnableLock [] messages;
	Object messageLock = new Object ();
	Thread syncThread;
	static final int GROW_SIZE = 4;
	static final int MESSAGE_LIMIT = 64;

	//TEMPORARY CODE
	static final boolean IS_CARBON = "carbon".equals (SWT.getPlatform ());
	static final boolean IS_COCOA = "cocoa".equals (SWT.getPlatform ());
	static final boolean IS_GTK = "gtk".equals (SWT.getPlatform ());

/**
 * Constructs a new instance of this class.
 * 
 * @param display the display to create the synchronizer on
 */
public Synchronizer (Display display) {
	this.display = display;
}
	
void addLast (RunnableLock lock) {
	boolean wake = false;
	synchronized (messageLock) {
		if (messages == null) messages = new RunnableLock [GROW_SIZE];
		if (messageCount == messages.length) {
			RunnableLock[] newMessages = new RunnableLock [messageCount + GROW_SIZE];
			System.arraycopy (messages, 0, newMessages, 0, messageCount);
			messages = newMessages;
		}
		messages [messageCount++] = lock;
		wake = messageCount == 1;
	}	
	if (wake) display.wakeThread ();
}

/**
 * Causes the run() method of the runnable to
 * be invoked by the user-interface thread at the next 
 * reasonable opportunity. The caller of this method continues 
 * to run in parallel, and is not notified when the
 * runnable has completed.
 *
 * @param runnable code to run on the user-interface thread.
 *
 * @see #syncExec
 */
protected void asyncExec (Runnable runnable) {
	if (runnable == null) {
		//TEMPORARY CODE
		if (!(IS_CARBON || IS_GTK || IS_COCOA)) {
			display.wake ();
			return;
		}
	}
	addLast (new RunnableLock (runnable));
}

int getMessageCount () {
	synchronized (messageLock) {
		return messageCount;
	}
}

void releaseSynchronizer () {
	display = null;
	messages = null;
	messageLock = null;
	syncThread = null;
}

RunnableLock removeFirst () {
	synchronized (messageLock) {
		if (messageCount == 0) return null;
		RunnableLock lock = messages [0];
		System.arraycopy (messages, 1, messages, 0, --messageCount);
		messages [messageCount] = null;
		if (messageCount == 0) {
			if (messages.length > MESSAGE_LIMIT) messages = null;
		}
		return lock;
	}
}

boolean runAsyncMessages () {
	return runAsyncMessages (false);
}

boolean runAsyncMessages (boolean all) {
	boolean run = false;
	do {
		RunnableLock lock = removeFirst ();
		if (lock == null) return run;
		run = true;
		synchronized (lock) {
			syncThread = lock.thread;
			try {
				lock.run ();
			} catch (Throwable t) {
				lock.throwable = t;
				SWT.error (SWT.ERROR_FAILED_EXEC, t);
			} finally {
				syncThread = null;
				lock.notifyAll ();
			}
		}
	} while (all);
	return run;
}

/**
 * Causes the run() method of the runnable to
 * be invoked by the user-interface thread at the next 
 * reasonable opportunity. The thread which calls this method
 * is suspended until the runnable completes.
 *
 * @param runnable code to run on the user-interface thread.
 *
 * @exception SWTException 
 *    ERROR_FAILED_EXEC - if an exception occurred when executing the runnable
 * 
 *
 * @see #asyncExec
 */
protected void syncExec (Runnable runnable) {
	RunnableLock lock = null;
	synchronized (Device.class) {
		if (display == null || display.isDisposed ()) SWT.error (SWT.ERROR_DEVICE_DISPOSED);
		if (!display.isValidThread ()) {
			if (runnable == null) {
				display.wake ();
				return;
			}
			lock = new RunnableLock (runnable);
			/*
			 * Only remember the syncThread for syncExec.
			 */
			lock.thread = Thread.currentThread();
			addLast (lock);
		}
	}
	if (lock == null) {
		if (runnable != null) runnable.run ();
		return;
	}
	synchronized (lock) {
		boolean interrupted = false;
		while (!lock.done ()) {
			try {
				lock.wait ();
			} catch (InterruptedException e) {
				interrupted = true;
			}
		}
		if (interrupted) {
			Compatibility.interrupt();
		}
		if (lock.throwable != null) {
			SWT.error (SWT.ERROR_FAILED_EXEC, lock.throwable);
		}
	}
}

}