Merge pull request #765 from adam-beneschan/742

changes to address kcooney's concerns about thread safety on issue #742

Author: kcooney

src/main/java/org/junit/internal/runners/statements/FailOnTimeout.java

@@ -17,7 +17,7 @@ public class FailOnTimeout extends Statement {
     private final TimeUnit fTimeUnit;
     private final long fTimeout;
     private final boolean fLookForStuckThread;
-    private ThreadGroup fThreadGroup = null;
+    private volatile ThreadGroup fThreadGroup = null;
 
     public FailOnTimeout(Statement originalStatement, long millis) {
         this(originalStatement, millis, TimeUnit.MILLISECONDS);

src/main/java/org/junit/rules/Timeout.java

@@ -36,7 +36,7 @@
 public class Timeout implements TestRule {
     private final long fTimeout;
     private final TimeUnit fTimeUnit;
-    private boolean fLookForStuckThread;
+    private final boolean fLookForStuckThread;
 
     /**
      * Create a {@code Timeout} instance with the timeout specified
@@ -70,6 +70,20 @@ public Timeout(long timeout, TimeUnit unit) {
         fLookForStuckThread = false;
     }
 
+    /**
+     * Create a {@code Timeout} instance with the same fields as {@code t}
+     * except for {@code fLookForStuckThread}.
+     *
+     * @param t the {@code Timeout} instance to copy
+     * @param lookForStuckThread whether to look for a stuck thread
+     * @since 4.12
+     */
+    protected Timeout(Timeout t, boolean lookForStuckThread) {
+        fTimeout = t.fTimeout;
+        fTimeUnit = t.fTimeUnit;
+        fLookForStuckThread = lookForStuckThread;
+    }
+
     /**
      * @param millis the timeout in milliseconds
      * @since 4.12
@@ -95,12 +109,11 @@ public static Timeout seconds(long seconds) {
      * @return This object
      * @since 4.12
      */
-    public Timeout lookForStuckThread(boolean enable) {
-        fLookForStuckThread = enable;
-        return this;
+    public Timeout lookingForStuckThread(boolean enable) {
+        return new Timeout(this, enable);
     }
 
     public Statement apply(Statement base, Description description) {
         return new FailOnTimeout(base, fTimeout, fTimeUnit, fLookForStuckThread);
     }
-}
+}

src/test/java/org/junit/tests/running/methods/TimeoutTest.java

@@ -199,7 +199,7 @@ public void failure(boolean mainThreadStalls) throws Exception {
 
     public static class InfiniteLoopWithStuckThreadTest {
         @Rule
-        public TestRule globalTimeout = new Timeout(100, TimeUnit.MILLISECONDS).lookForStuckThread(true);
+        public TestRule globalTimeout = new Timeout(100, TimeUnit.MILLISECONDS).lookingForStuckThread(true);
 
         @Test
         public void failure() throws Exception {
@@ -209,7 +209,7 @@ public void failure() throws Exception {
 
     public static class InfiniteLoopStuckInMainThreadTest {
         @Rule
-        public TestRule globalTimeout = new Timeout(100, TimeUnit.MILLISECONDS).lookForStuckThread(true);
+        public TestRule globalTimeout = new Timeout(100, TimeUnit.MILLISECONDS).lookingForStuckThread(true);
 
         @Test
         public void failure() throws Exception {