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Re: [rap-dev] ModalContext 
Hi Igor,
as a rule of thumb, if RAP works differently than RCP, it is a bug. To fix the bug, it should be fixed in RWT and not in the upper layers (Workbench, JFace, etc). 

I filed this bug for the issues with calling (a)syncExec( null ):
  280829: [Display] calling syncExec/asyncExec(null) behaves
  differently in SWT
  https://bugs.eclipse.org/bugs/show_bug.cgi?id=280829
It should be relatively easy to fix this.
As far as I understand, the second and third remark are related to synchronization. Your follow-up posting also describes synchronization issues. Please correct me if I'm wrong.
One way to solve these problems could be to take the Synchronizer class from SWT and use it instead of the code in UICallBackManager. Some additions to the Synchronizer class would be necessary like calling UICallBackManager#sendUICallBack() from synchExec, etc. Also sleep/readAndDispatch would need to be reworked to make use of the Synchronizer methods/lock objects. Then timerExec() would to need be reworked to fit into the Synchronizer mechanism. Plus whatever I overlooked so far... The positive aspect of this way is that we re-use the SWT synchronization code. The downside is that a lot of the existing code would have to be changed, which is probably more time-consuming than just fixing the issues at hand.
What I would appreciate most, are JUnit test cases that demonstrate the use case and currently fail. With these test cases we could then address one issue after another. 

Cheers,
Rüdiger


mail.apptech.nichost.ru wrote:

Hello

It seems that the ModalContext functionality should be reimplemented on RAP
(it is ported from RCP now).

First remark: look at the
org.eclipse.jface.operation.ModalContext.ModalContextThread.run(). There is
a call: "display.asyncExec(null);". On RCP such call have a special meaning.
This call causes display thread to wake up.

Maybe this call ("display.asyncExec(null);") should be removed from the
org.eclipse.jface.operation.ModalContext.ModalContextThread.run() ?
Alternative maybe Display#asyncExec should be reimplemented (and also
syncExec) for the case where runnable is null?

Second remark:

There is another part of code in the
org.eclipse.jface.operation.ModalContext.ModalContextThread.run():

display.syncExec(new Runnable() {
  public void run() {
    // do nothing
  }
});

On RAP this code causes deadlocks with
org.eclipse.jface.operation.ModalContext.ModalContextThread.block() method.
Moreover, there is a problem with
org.eclipse.rwt.internal.lifecycle.UICallBackManager.SyncRunnable and
ModalContext. As you know, SyncRunnable has a block() method, wich blocks
the thread that called
org.eclipse.rwt.internal.lifecycle.UICallBackManager.addSync(Display,
Runnable) method. The blocked thread will wait on special lock object until
the notification from other thread (with should call SyncRunnable#run
method). But when you are using ModalContext the other thread will blocked
on runnablesLock.

I think the problem in the
org.eclipse.rwt.internal.lifecycle.UICallBackManager.addSync(Display,
Runnable) method.

Third remark:

// Make sure that all events in the asynchronous event queue
// are dispatched.
display.syncExec(new Runnable() {
  public void run() {
    // do nothing
  }
});

This code do not the things that declared in comments.

Last remark: "display.asyncExec(null);" can be implemented correctly, but
you have to place additional synchronization string in
org.eclipse.jface.operation.ModalContext.ModalContextThread.run() to prevent
ending of execution
org.eclipse.jface.operation.ModalContext.ModalContextThread.run() before
display.sleep() occures in
org.eclipse.jface.operation.ModalContext.ModalContextThread.block() method.

Place

synchronized (display.getThread()) {
}
before 
// Stop event dispatching
continueEventDispatching = false;

The display.getThread() returns UIThread instance. So it will be locked
until the switchThread notification from display.sleap() method.

Thank you, Igor


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