<AWT Dev> [8] Review request for 8015730: PIT: On Linux, OGL=true and fbobject=false leads to deadlock or infinite loop

Anthony Petrov anthony.petrov at oracle.com
Mon Jul 1 09:50:03 PDT 2013

Thanks for the additional information, Anton. Since this fix simply 
reverts the behavior in GLXSurfaceData.c back to the pre-8005607 era, it 
could probably be considered a good interim solution for the problem.

I'd like to hear Artem's opinion on this, though. Should we file a P4 
bug to investigate the issue further so that in the future we could 
avoid calling XSync() w/o the AWTLock?

best regards,

On 07/01/2013 07:24 PM, Anton Litvinov wrote:
> Hello Anthony,
> Thank you for the review of this fix. I would like to remark that this
> deadlock is a regression of the fix for the bug 8005607, and in the code
> of the file "jdk/src/solaris/native/sun/java2d/opengl/GLXSurfaceData.c"
> before 8005607 fix, where the previous XError handling mechanism not
> involving "sun.awt.X11.XErrorHandlerUtil" class was used, native
> "XSync()" function was called without acquiring of AWT lock. So a fix
> for the current bug with a deadlock just reverted a part of the fix
> 8005607 which enforced taking AWT lock from the function
> "Java_sun_java2d_opengl_GLXSurfaceData_initPbuffer" in the file
> "jdk/src/solaris/native/sun/java2d/opengl/GLXSurfaceData.c". Answers to
> your questions are provided below.
> 1. "AWT EventQueue" holds AWT lock and waits till "Java2D Queue Flusher"
> thread finishes its job, because in the method
> "sun.java2d.opengl.OGLSurfaceData.initSurface(final int width, final int
> height)" execution of "initSurfaceNow(int width, int height)" is
> dispatched to "Java2D Queue Flusher". Before this dispatching in the
> method "initSurface" AWT lock is taken by the lines
>      308        OGLRenderQueue rq = OGLRenderQueue.getInstance();
>      309        rq.lock();
> and then with held AWT lock "AWT EventQueue" thread starts waiting on
> the second lock "sun.java2d.opengl.OGLRenderQueue.flusher" in the method
> "sun.java2d.opengl.OGLRenderQueue.QueueFlusher.flushNow()"
>      181                    wait();
> 2. Yes, I investigated the option of waiting on AWT lock instead of
> "sun.java2d.opengl.OGLRenderQueue.flusher" lock in the class
> "sun.java2d.opengl.OGLRenderQueue", but this is impossible, because
> access to the always running thread "Java2D Queue Flusher" should be
> synchronized on some lock other than AWT lock, otherwise there will be a
> performance degradation, because it will be trying to get AWT lock each
> 100 milliseconds. As I understood a possible solution for this problem
> can be not locking on AWT lock before dispatching execution of any code
> to "Java2D Queue Flusher" or complete refactoring of locking mechanism
> in the class "sun.java2d.opengl.OGLRenderQueue". Since the current bug
> blocks SQE from running any tests involving OpenGL and does not allow to
> run any Java GUI application with enabled OpenGL rendering on Linux OS,
> I suppose the variant of refactoring is not acceptable. That is why as
> the most secure solution I decided just to call XSync() from
> "jdk/src/solaris/native/sun/java2d/opengl/GLXSurfaceData.c" as it was
> before the fix for 8005607.
> Thank you,
> Anton
> On 7/1/2013 3:11 PM, Anthony Petrov wrote:
>> Hi Anton,
>> I'm not sure if this a good fix since it enabled the GL thread to call
>> Xlib APIs w/o acquiring the AWTLock. This may not present a problem
>> currently since we know exactly when this method is called and that
>> another thread is holding the lock and isn't calling other X11
>> functions at the moment. But I doubt this knowledge will be widely
>> known and remembered in the future, and if another thread starts
>> calling X11 routines, we'll get into trouble...
>> Why would another thread (the AWT EventQueue if I got the problem
>> right) hold the AWTLock and wait till the GL thread finishes its job?
>> I'd assume it should release the lock for the period of waiting. This
>> would allow the GL thread to acquire the lock and perform the XSync()
>> call w/o any potential issues. Have you investigated this option?
>> --
>> best regards,
>> Anthony
>> On 06/28/2013 09:16 PM, Anton Litvinov wrote:
>>> Hello,
>>> Could you please review the following fix for a bug, which consists in a
>>> deadlock provoked by concurrency between AWT-EventQueue and Java2D Queue
>>> Flusher for taking AWT lock, when OpenGL rendering is enabled.
>>> Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8015730
>>> Webrev: http://cr.openjdk.java.net/~alitvinov/8015730/webrev.00
>>> The fix allows the code from the native function
>>> "Java_sun_java2d_opengl_GLXSurfaceData_initPbuffer" of the file
>>> "jdk/src/solaris/native/sun/java2d/opengl/GLXSurfaceData.c" execute all
>>> XError handling procedures using "sun.awt.X11.XErrorHandlerUtil" class
>>> without acquiring AWT lock. It is the only available solution for this
>>> problem, because the current design of
>>> "sun.java2d.opengl.OGLRenderQueue" class does not allow to take AWT lock
>>> in Java2D Queue Flusher thread without reaching a deadlock, since all
>>> calls to the method
>>> "sun.java2d.opengl.OGLRenderQueue.flushAndInvokeNow(Runnable r)" are
>>> guarded by AWT lock.
>>> Thank you,
>>> Anton

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