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

[Anton Litvinov]

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