<Swing Dev> [11][JDK-8176512][TEST_BUG] add a minimal delay to java/awt/Paint/bug8024864.java

[Sergey Bylokhov]

On 02/02/2018 04:19, Krishna Addepalli wrote:
> Hi Sergey,
> 
> "It does not guarantee but this wait + waitForIdle() should be enough."
> If it is not guaranteed, how can we say it is enough?

Because it will flush the native queue a few times, then flush EDT, and 
then it will wait 100 ms(minimum).

> "Take a look to the code which generates the OPEN_EVENT used in the fix(see Window.show()).
> It is posted without relation to the native peer:"
> 
> This is incorrect, since before posting the OPEN_EVENT, there is a "super.show()" call which ultimately leads to AwtComponent::_Show function in awt_Component.cpp, which actually posts a message to show the window.

If it is incorrect then why do you need to wait when OPEN_EVENT will be 
dispatched at all, since you mention that "super.show()" call which 
ultimately leads to AwtComponent::_Show function". So 
AwtComponent::_Show will be called before the end of Window.show().

The approach which you used in the fix(wait for OPEN_EVENT) is identical 
to implementation of waitForIdle().
  - Both will post events(OPEN_EVENT/dummy) after Window.show();
  - Both will wait when it will be dispatched.

But only waitForIdle() will flush the native, and can do this a few 
time(EDT/native/EDT/native etc).

> Also, before OPEN_EVENT, ComponentShown event is also posted(if there are active listeners to the component) which also seems to be coming from native side.
> So, I think it is more appropriate to rely on OPEN_EVENT or even ComponentShown event, rather than having to use wait.

My point is that the fix and previous implementation is mostly 
identical. And if old implementation does not work then it is a bug 
somewhere in the robot. See example below which compare both cases:

> ==========
> 1) EDT: Window.setVisible()->Window.show()->Window.postWindowEvent()->
> barrier.await();
> 2) Main: blocked by barrier.await();
> 
> So your code waits when the setVisible() will complete and some additional event
> (OPEN_EVENT) will be dispatched by EDT.
> 
> ==========
> The usage of waitForIdle() should produce similar result:
> 
> 1) EDT: Window.setVisible()->Window.show();
> 3) Main: post dummy event to EDT->waitLock.notifyAll();
> 2) Main: blocked in SunToolkit.waitForIdle() by waitLock.wait();
> 
> The old code waits when the setVisible() will complete and some additional event
> (dummy) will be dispatched by EDT. But it also flush the native queue.
> 
> So it is still unclear why waitForIdle does not work.


-- 
Best regards, Sergey.