Fix "no more handles" exception during Edge browser creation

[HeikoKlare]

The Edge browser creation uses Display.readAndDispath() to process the OS events for browser instantiation. When there are other asynchronous executions scheduled while the browser is being initialized, they may be processed in between the processing of browser-instantiating OS events if too much time elapses between them. In case such an asynchronous execution changes a state that makes the browser instantiation fail, such as disposing the composite parent of the browser, an exception occurs.

In order to avoid the processing of asynchronous executions during browser instantiation, the change ensures that readAndDisplay() is only called when an OS event is present to be processed.

A drawback of this approach is that in case the browser instantiation takes a long time, for whatever reasons, the UI will not be responsive as UI events are not processed. I do not think that this situation is likely to happen but want to mention it as a potential drawback of the solution.

Supposed to fix #339.

[github-actions]

Test Results

     299 files  ±0       299 suites  ±0   8m 15s ⏱️ + 2m 25s
  4 086 tests +1    4 053 ✔️  - 22    8 💤 ±0  25 ❌ +23 
12 176 runs  +3  12 081 ✔️  - 20  70 💤 ±0  25 ❌ +23 

For more details on these failures, see this check.

Results for commit ed8f821. ± Comparison against base commit 86616f0.

♻️ This comment has been updated with latest results.

[vogella]

Thanks @HeikoKlare this affected on of my clients in the past. I suggest to merge.

[Destrolaric]

We also had to patch the issue behavior. It will be good to finally make it work properly inside the SWT. I would be glad if it would be merged.

[HeikoKlare]

@Destrolaric can you already say whether this change makes your patch obsolete and fixes the behavior properly for you?

From my side, we can merge this PR. I have validated proper instantiation of the Edge browser on my system in an isolated SWT application as well as in our RCP product. Should someone else validate before merging?

[lshanmug]

@deepika-u Can you please verify the patch?

[deepika-u]

@HeikoKlare

I have tried to recreate the problem of "No more handles" with below Snippet.

package org.eclipse.swt.bugs;

import org.eclipse.swt.;
import org.eclipse.swt.browser.;
import org.eclipse.swt.layout.;
import org.eclipse.swt.widgets.;

public class NoMoreHandles {

public static void main(String[] args) {
	// TODO Auto-generated method stub
	Display display = new Display();
	Shell shell = new Shell(display);
	shell.setLayout(new GridLayout(1, false));

	createComposite(shell);

	shell.pack();
	shell.open();
	while (!shell.isDisposed()) {
		if (!display.readAndDispatch())
			display.sleep();
	}
	display.dispose();
}

public static void createComposite(Composite parent) {
	parent.setLayout(new GridLayout(1, false));

	for (int i = 0; i <= 10; i++) {
		System.out.println("Iteration " + i);
		Composite c = new Composite(parent, SWT.NONE);
		Display.getCurrent().asyncExec(new Runnable() {

			@Override
			public void run() {
				c.dispose();
			}
		});
		Browser browser = null;
		if (!c.isDisposed()) {
			browser = new Browser(c, SWT.EDGE);
		}
		if (browser != null) {
			browser.dispose();
		}
	}
}

}

When run seeing the below console output
Iteration 0
Exception in thread "main" org.eclipse.swt.SWTError: No more handles [0x80070578]
at org.eclipse.swt.SWT.error(SWT.java:4944)
at org.eclipse.swt.browser.Edge.error(Edge.java:190)
at org.eclipse.swt.browser.Edge.create(Edge.java:343)
at org.eclipse.swt.browser.Browser.(Browser.java:99)
at org.eclipse.swt.bugs.NoMoreHandles.createComposite(NoMoreHandles.java:42)
at org.eclipse.swt.bugs.NoMoreHandles.main(NoMoreHandles.java:16)

Then when i apply the patch, i am able to run it fine and not seeing any "No more handles".
So the patch looks fine for me. Please let me know if that verifies the fix and you want me to check anything else.

I have tried on below environment
Eclipse SDK
Version: 2023-06 (4.28)
Build id: I20230507-1800
OS: Windows 11, v.10.0, x86_64 / win32
Java vendor: Eclipse Adoptium
Java runtime version: 20+36
Java version: 20

[deepika-u]

@HeikoKlare

Specifically tried for Edge browser with below snippet once again and edge browser window comes up properly after the patch is applied.

package org.eclipse.swt.bugs;

import org.eclipse.swt.;
import org.eclipse.swt.browser.;
import org.eclipse.swt.layout.;
import org.eclipse.swt.widgets.;

public class NoMoreHandles {

public static void main(String[] args) {
	// TODO Auto-generated method stub
	Display display = new Display();
	Shell shell = new Shell(display);
	shell.setLayout(new FillLayout());

	createComposite(shell);

	shell.pack();
	shell.open();
	while (!shell.isDisposed()) {
		if (!display.readAndDispatch())
			display.sleep();
	}
	display.dispose();
}

public static void createComposite(Composite parent) {
	//parent.setLayout(new GridLayout(1, false));

	for (int i = 0; i < 1; i++) {
		//for (int i = 0; i <= 10; i++) {
		System.out.println("Iteration " + i);
		Composite c = new Composite(parent, SWT.NONE);
		c.setLayout(new FillLayout());
		Display.getCurrent().asyncExec(new Runnable() {

			@Override
			public void run() {
				//c.dispose();
			}
		});
		Browser browser = null;
		if (!c.isDisposed()) {
			browser = new Browser(c, SWT.EDGE);
			browser.setSize(100, 100);
			browser.setUrl("whatismybrowser.com");
			//browser.setText("welcome");
		}
		if (browser != null) {
			//browser.dispose();
		}
	}
}

}

So patch looks good to me.

[niraj-modi]

Approving, Thanks @deepika-u for verifying the patch.

[HeikoKlare]

Great, thanks for verifying, @deepika-u!

[deepika-u]

Verified this on below build and looks good to me.

Eclipse SDK
Version: 2023-06 (4.28)
Build id: I20230515-1800
OS: Windows 11, v.10.0, x86_64 / win32
Java vendor: Eclipse Adoptium
Java runtime version: 17.0.6+10
Java version: 17.0.6