[historyView] Perform clear on background thread when disposed

An NPE can occur if SWTCommitList.clear() is called
from dispose() while fillTo() is running from
GenerateHistoryJob.

dispose() is always called on the UI-thread so schedule
a background thread that synchronizes on the instance
and calls clear since all other state accessing calls to
the SWTCommitList instance are done inside synchronized
blocks.

Change-Id: I855d5bfeb5131c634b4790e6b7231424f2be4566

1 files changed, 17 insertions, 1 deletions

diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/SWTCommitList.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/SWTCommitList.java
index 6a84ea5598..36603dd530 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/SWTCommitList.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/SWTCommitList.java
@@ -11,6 +11,10 @@ package org.eclipse.egit.ui.internal.history;
 import java.util.ArrayList;
 import java.util.LinkedList;
 
+import org.eclipse.core.runtime.IProgressMonitor;
+import org.eclipse.core.runtime.IStatus;
+import org.eclipse.core.runtime.Status;
+import org.eclipse.core.runtime.jobs.Job;
 import org.eclipse.jgit.revplot.PlotCommitList;
 import org.eclipse.jgit.revplot.PlotLane;
 import org.eclipse.swt.events.DisposeEvent;
@@ -53,7 +57,19 @@ class SWTCommitList extends PlotCommitList<SWTCommitList.SWTLane> implements Dis
 	}
 
 	public void dispose() {
-		clear();
+		Job clearJob = new Job("Clearing commit list") { //$NON-NLS-1$
+
+			@Override
+			protected IStatus run(IProgressMonitor monitor) {
+				synchronized (SWTCommitList.this) {
+					clear();
+				}
+				return Status.OK_STATUS;
+			}
+		};
+		clearJob.setSystem(true);
+		clearJob.schedule();
+
 		for (Color color : allColors)
 			color.dispose();
 		if (!control.isDisposed())