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Refreshing RWT standalone throws exception [message #908754]

Wed, 05 September 2012 20:19

Eclipse User

I've built a proof of concept rwt standalone single source app.

Every second time I restart the session by pressing F5 I get the following exception:

2012-09-06 12:11:37.909:WARN:oejs.ServletHandler:ERROR:  /ucv
java.lang.NullPointerException
	at org.eclipse.swt.widgets.Synchronizer.removeFirst(Synchronizer.java:145)
	at org.eclipse.swt.widgets.Synchronizer.releaseSynchronizer(Synchronizer.java:127)
	at org.eclipse.swt.widgets.Display.release(Display.java:688)
	at org.eclipse.swt.graphics.Device.dispose(Device.java:287)
	at org.eclipse.rap.rwt.internal.lifecycle.SimpleLifeCycle$SimpleSessionShutdownAdapter$1.run(SimpleLifeCycle.java:92)
	at org.eclipse.rap.rwt.internal.lifecycle.FakeContextUtil.runNonUIThreadWithFakeContext(FakeContextUtil.java:58)
	at org.eclipse.rap.rwt.internal.lifecycle.SimpleLifeCycle$SimpleSessionShutdownAdapter.interceptShutdown(SimpleLifeCycle.java:87)
	at org.eclipse.rap.rwt.internal.service.SessionStoreImpl.valueUnbound(SessionStoreImpl.java:182)
	at org.eclipse.rap.rwt.internal.service.LifeCycleServiceHandler.clearSessionStore(LifeCycleServiceHandler.java:155)
	at org.eclipse.rap.rwt.internal.service.LifeCycleServiceHandler.reinitializeSessionStore(LifeCycleServiceHandler.java:140)
	at org.eclipse.rap.rwt.internal.service.LifeCycleServiceHandler.handlePostRequest(LifeCycleServiceHandler.java:88)
	at org.eclipse.rap.rwt.internal.service.LifeCycleServiceHandler.synchronizedService(LifeCycleServiceHandler.java:67)
	at org.eclipse.rap.rwt.internal.service.LifeCycleServiceHandler.service(LifeCycleServiceHandler.java:58)
	at org.eclipse.rap.rwt.engine.RWTServlet.handleValidRequest(RWTServlet.java:101)
	at org.eclipse.rap.rwt.engine.RWTServlet.doPost(RWTServlet.java:80)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:755)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
	at org.eclipse.rap.rwt.osgi.internal.CutOffContextPathWrapper.service(CutOffContextPathWrapper.java:106)
	at org.eclipse.equinox.http.servlet.internal.ServletRegistration.service(ServletRegistration.java:61)
	at org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:128)
	at org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:60)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
	at org.eclipse.equinox.http.jetty.internal.HttpServerManager$InternalHttpServiceServlet.service(HttpServerManager.java:384)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:598)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:486)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1065)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:413)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:192)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:999)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:111)
	at org.eclipse.jetty.server.Server.handle(Server.java:350)
	at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:454)
	at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:900)
	at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:954)
	at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:851)
	at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
	at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:77)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:606)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:46)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:603)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:538)
	at java.lang.Thread.run(Unknown Source)

The session starts correctly. The first restart (by pressing F5) throws the exception. Every second F5 from then on throws the same exception.
Any ideas? I'm using the nightly RAP 2.0 build 20120904-0111

The messageLock field in Synchronizer is null, which leads me to believe its releaseSynchronizer method is being called twice, but the only call I can find to that method is wraped in the if (!isDisposed) {... block in Device#dispose

Re: Refreshing RWT standalone throws exception [message #908770 is a reply to message #908754]

Wed, 05 September 2012 21:13

Eclipse User

It looks like the problem is caused by adding a DisposeListener to a Shell that calls Display.dispose.

I did this so the RCP launch bundle can call the application startup method (which creates various shells during the login process) then just spin the event loop like so

	public Object start(IApplicationContext context) throws Exception {
... call startup method
		while (!display.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}
		return EXIT_OK;
	}

While the RWT launch bundle EntryPoint simply calls the application startup method.

	public int createUI() {
...call startup method
	    return 0;
	}

I suppose I can pass a runnable to the startup method that gets call when the application should shut down. RWT impl can be empty and RCP impl can set a flag that is tested in the while() loop along with Display.isDisposed

Re: Refreshing RWT standalone throws exception [message #908888 is a reply to message #908770]

Thu, 06 September 2012 03:16

Eclipse User

Hi Chris,
your application is running in SWT_COMPATIBILITY mode [1]. Isn't it? In
this case you need readAndDispatch loop in your entry point as well....
Or I didn't understand you correctly.

[1]
http://help.eclipse.org/juno/index.jsp?topic=%2Forg.eclipse.rap.help%2Fhelp%2Fhtml%2Freference%2Fapi%2Forg%2Feclipse%2Frwt%2Fapplication%2FApplication.OperationMode.html
Best,
Ivan

On 9/6/2012 4:13 AM, Chris Fairhall wrote:
> It looks like the problem is caused by adding a DisposeListener to a
> Shell that calls Display.dispose.
>
> I did this so the RCP launch bundle can call the application startup
> method (which creates various shells during the login process) then
> just spin the event loop like so
>
> public Object start(IApplicationContext context) throws Exception {
> .. call startup method
> while (!display.isDisposed()) {
> if (!display.readAndDispatch()) {
> display.sleep();
> }
> }
> return EXIT_OK;
> }
>
>
> While the RWT launch bundle EntryPoint simply calls the application
> startup method.
>
> public int createUI() {
> ..call startup method
> return 0;
> }
>
>
> I suppose I can pass a runnable to the startup method that gets call
> when the application should shut down. RWT impl can be empty and RCP
> impl can set a flag that is tested in the while() loop along with
> Display.isDisposed

--
Ivan Furnadjiev

Twitter: @EclipseRAP
Blog: http://eclipsesource.com/blogs/

Professional services for RAP and RCP?
http://eclipsesource.com/services/rap/

Re: Refreshing RWT standalone throws exception [message #909375 is a reply to message #908888]

Thu, 06 September 2012 23:43

Eclipse User

No, When running as RWT it's running under JEE mode (hence the reference to SimpleLifeCycle in the stack trace). A requirement is session replication. I'm not actually using the Eclipse Workbench.

Re: Refreshing RWT standalone throws exception [message #909442 is a reply to message #909375]

Fri, 07 September 2012 02:31

Eclipse User

Chris,
could you provide some code snippets to demonstrate (reproduce) the issue?
Best,
Ivan

On 9/7/2012 6:43 AM, Chris Fairhall wrote:
> No, When running as RWT it's running under JEE mode (hence the
> reference to SimpleLifeCycle in the stack trace). A requirement is
> session replication. I'm not actually using the Eclipse Workbench.

--
Ivan Furnadjiev

Twitter: @EclipseRAP
Blog: http://eclipsesource.com/blogs/

Professional services for RAP and RCP?
http://eclipsesource.com/services/rap/

Re: Refreshing RWT standalone throws exception [message #910524 is a reply to message #909442]

Sun, 09 September 2012 19:09

Eclipse User

Attached is an example project to replicate the issue.

Here is the code:

public class EntryPoint implements IEntryPoint {
	@Override
	public int createUI() {
		Shell shell = new Shell();
		shell.addDisposeListener(new DisposeListener() {
			@Override
			public void widgetDisposed(DisposeEvent event) {
				Display.getCurrent().dispose();
			}
		});
		shell.setSize(200, 200);
		shell.setVisible(true);

	    return 0;
	}
}

Pressing F5 throws an exception every second time.

Attachment: rwttest.zip
(Size: 4.72KB, Downloaded 246 times)

Re: Refreshing RWT standalone throws exception [message #911766 is a reply to message #910524]

Wed, 12 September 2012 05:22

Eclipse User

Chris,

You should not call Display#dispose() in a dispose listener (actually,
you should not call this method at all in RAP). Here's what happens:

- Browser refresh leads to a disposal of the display
- In Display#dispose(), all Shells are disposed of
- Your dispose listener is notified which calls display dispose
-> Display#dispose() is called during Display#dispose() ⚡

The same code leads to a "widget is disposed" exception in SWT. When you
add a button to your snippet that disposes of the display, you'll see
this exception. I've opened a bug [1] to throw the appropriate SWT
exception in RAP as well.

What is the display.dispose() call supposed to achieve in your application?

Regards,
Ralf

[1] 389384: Calling Display#dispose() during disposal of the display
should throw SWT exception
https://bugs.eclipse.org/bugs/show_bug.cgi?id=389384

--
Ralf Sternberg

Twitter: @EclipseRAP
Blog: http://eclipsesource.com/blogs/

Professional services for RAP and RCP?
http://eclipsesource.com/services/rap/

Re: Refreshing RWT standalone throws exception [message #912037 is a reply to message #911766]

Wed, 12 September 2012 16:44

Eclipse User

You're right, I shouldn't have called dispose in a dispose listener.
It was supposed to ensure the event loop that the RCP version has doesn't continue running. I have since implemented another method of doing this.

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