Avoid BusyIndicator putting Display to sleep after being done

Due to a race condition between the BusyIndicator's event loop spinning
and the display.wake() call performed after the future to wait for is
done, the BusyIndicator execution may get stuck in a display.sleep()
call. While on Windows and MacOS the wake() call will effectively still
ensure that display.sleep() return immediately if invoked
display.sleep() was called, this is neither guaranteed nor does that
happen on Linux.

This fixes the race condition by replacing the wake() call in the future
with scheduling an empty task that ensures that the event queue remains
spinned (like everywhere else).

Contributes to
#3044

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/BusyIndicator.java

@@ -34,6 +34,8 @@ public class BusyIndicator {
 	static final String BUSYID_NAME = "SWT BusyIndicator"; //$NON-NLS-1$
 	static final String BUSY_CURSOR = "SWT BusyIndicator Cursor"; //$NON-NLS-1$
 
+	private static final Runnable DO_NOTHING = () -> {};
+
 	/**
 	 * Runs the given <code>Runnable</code> while providing
 	 * busy feedback using this busy indicator.
@@ -111,10 +113,14 @@ public static void showWhile(Future<?> future) {
 						stage.handle((nil1, nil2) -> {
 							if (!display.isDisposed()) {
 								try {
-									display.wake();
+									// Use asyncExec() to wake up the display thread instead of wake()
+									// as this call may happen between the future.isDone() check and the
+									// display.sleep() call such that a wake() may get lost whereas an asyncExec()
+									// will wake up the sleep() even if it is scheduled before calling sleep()
+									display.asyncExec(DO_NOTHING);
 								} catch (SWTException e) {
-									// ignore then, this can happen due to the async nature between our check for
-									// disposed and the actual call to wake the display can be disposed
+									// ignore; due to the async nature between our disposed check and scheduling
+									// asyncExec(), the display may already be disposed
 								}
 							}
 							return null;