Fix for issue #55: ThreadMonitor waits unnecessarily

src/main/java/delight/nashornsandbox/internal/ThreadMonitor.java

@@ -83,7 +83,9 @@ void run() {
 		try {
 			// wait, for threadToMonitor to be set in JS evaluator thread
 			synchronized (monitor) {
-				monitor.wait(maxCPUTime / MILI_TO_NANO);
+				if (threadToMonitor == null) {
+					monitor.wait(maxCPUTime / MILI_TO_NANO);
+				}
 			}
 			if (threadToMonitor == null) {
 				throw new IllegalStateException("Executor thread not set after " + maxCPUTime / MILI_TO_NANO + " ms");

src/test/java/delight/nashornsandbox/internal/ThreadMonitorTest.java

@@ -0,0 +1,26 @@
+package delight.nashornsandbox.internal;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * JUnit test for ThreadMonitor.
+ */
+public class ThreadMonitorTest {
+
+	/**
+	 * This is a simple test that verifies that if the thread to monitor is already set, the ThreadMonitor does not
+	 * wait unnecessarily when it is run.
+	 */
+	@Test
+	public void when_run_and_threadToMonitor_set_then_do_not_wait() {
+		final ThreadMonitor threadMonitor = new ThreadMonitor(1000, 0);
+		Thread threadToMonitor = new Thread();
+		threadMonitor.setThreadToMonitor(threadToMonitor);
+		threadMonitor.stopMonitor();
+
+		long startTime = System.currentTimeMillis();
+		threadMonitor.run();
+		Assert.assertTrue(System.currentTimeMillis() - startTime < 500);
+	}
+}