Allow the ProgressProvider to control the used instance of a monitor

This enables the ProgressProvider to decide the instance of the
ProgressMonitor used in beginRule / join / suspend operations.

This is important if the progressprovider needs to react to certain
actions, e.g. in an UI a provider might make sure the UI is responsive
or show a "terminate" button even if the job is currently waiting on a
rule.

Fix eclipse-platform#40

bundles/org.eclipse.core.jobs/src/org/eclipse/core/internal/jobs/JobManager.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2003, 2020 IBM Corporation and others.
+ * Copyright (c) 2003, 2022 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -20,7 +20,8 @@
  *     Jan Koehnlein - Fix for bug 60964 (454698)
  *     Terry Parker - Bug 457504, Publish a job group's final status to IJobChangeListeners
  *     Xored Software Inc - Fix for bug 550738
- *     Christoph Laeubrich - remove deprecated API
+ *     Christoph Laeubrich 	- remove deprecated API
+ *      					- Issue #40 - UI freezes when a ThreadJob is waiting to run in the UI Thread 
  *******************************************************************************/
 package org.eclipse.core.internal.jobs;
 
@@ -1100,19 +1101,17 @@ boolean join(InternalJobGroup jobGroup, long timeout, IProgressMonitor monitor)
 	}
 
 	/**
-	 * Returns a non-null progress monitor instance.  If the monitor is null,
-	 * returns the default monitor supplied by the progress provider, or a
+	 * Returns a non-null progress monitor instance. If a progress provider is
+	 * given, returns the monitor for this supplied by the progress provider, or a
 	 * NullProgressMonitor if no default monitor is available.
 	 */
 	private IProgressMonitor monitorFor(IProgressMonitor monitor) {
-		if (monitor == null || (monitor instanceof NullProgressMonitor)) {
-			if (progressProvider != null) {
-				try {
-					monitor = progressProvider.getDefaultMonitor();
-				} catch (Exception e) {
-					String msg = NLS.bind(JobMessages.meta_pluginProblems, JobManager.PI_JOBS);
-					RuntimeLog.log(new Status(IStatus.ERROR, JobManager.PI_JOBS, JobManager.PLUGIN_ERROR, msg, e));
-				}
+		if (progressProvider != null) {
+			try {
+				return Objects.requireNonNull(progressProvider.monitorFor(monitor), "ProgressProvider returned null!"); //$NON-NLS-1$
+			} catch (Exception e) {
+				String msg = NLS.bind(JobMessages.meta_pluginProblems, JobManager.PI_JOBS);
+				RuntimeLog.log(new Status(IStatus.ERROR, JobManager.PI_JOBS, JobManager.PLUGIN_ERROR, msg, e));
 			}
 		}
 

bundles/org.eclipse.core.jobs/src/org/eclipse/core/runtime/jobs/ProgressProvider.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2003, 2012 IBM Corporation and others.
+ * Copyright (c) 2003, 2022 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -10,6 +10,7 @@
  *
  * Contributors:
  *     IBM Corporation - initial API and implementation
+ *     Christoph Läubrich - Issue #40 - UI freezes when a ThreadJob is waiting to run in the UI Thread
  *******************************************************************************/
 package org.eclipse.core.runtime.jobs;
 
@@ -96,4 +97,24 @@ public IProgressMonitor createMonitor(Job job, IProgressMonitor group, int ticks
 	public IProgressMonitor getDefaultMonitor() {
 		return new NullProgressMonitor();
 	}
+
+	/**
+	 * Returns a (possibly wrapped) progress monitor to use when running the job.
+	 * <p>
+	 * This default implementation returns ProgressProvider#getDefaultMonitor() when
+	 * the monitor is <code>null</code> or an instance of
+	 * {@link NullProgressMonitor} and the passed instance otherwise. Subclasses may
+	 * override.
+	 *
+	 * @param monitor the monitor to wrap, might be null
+	 * @return a progress monitor, either wrapped or the passed instance but never
+	 *         <code>null</code>
+	 * @since 3.13
+	 */
+	public IProgressMonitor monitorFor(IProgressMonitor monitor) {
+		if (monitor == null || monitor instanceof NullProgressMonitor) {
+			return getDefaultMonitor();
+		}
+		return monitor;
+	}
 }