Make MyersDiff interruptible

For some specific file, MyersDiff goes into an infinite loop[1]. Since
this problem is hard to reproduce and possibly harder to fix, this
change makes the MyersDiff interruptible so the diff can be aborted at
least when such infinite loop happens.

[1]https://bugs.eclipse.org/bugs/show_bug.cgi?id=444623

Change-Id: I6e006ccb122d1e68c9846a24d5399d94776c2858
Signed-off-by: Hugo Arès <hugo.ares@ericsson.com>

org.eclipse.jgit/src/org/eclipse/jgit/diff/MyersDiff.java

@@ -46,6 +46,7 @@ package org.eclipse.jgit.diff;
 
 import java.text.MessageFormat;
 
+import org.eclipse.jgit.errors.DiffInterruptedException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.util.IntList;
 import org.eclipse.jgit.util.LongList;
@@ -406,6 +407,9 @@ if (k < beginK || k > endK)
 				// TODO: move end points out of the loop to avoid conditionals inside the loop
 				// go backwards so that we can avoid temp vars
 				for (int k = endK; k >= beginK; k -= 2) {
+					if (Thread.interrupted()) {
+						throw new DiffInterruptedException();
+					}
 					int left = -1, right = -1;
 					long leftSnake = -1L, rightSnake = -1L;
 					// TODO: refactor into its own function

org.eclipse.jgit/src/org/eclipse/jgit/errors/DiffInterruptedException.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2015 Ericsson
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.errors;
+
+/**
+ * Thrown when a thread executing a diff is interrupted
+ *
+ * @see org.eclipse.jgit.diff.MyersDiff
+ */
+public class DiffInterruptedException extends RuntimeException {
+	private static final long serialVersionUID = 1L;
+}