#727 Fail on timeout displays stack of stuck thread

.settings/org.eclipse.jdt.core.prefs

@@ -247,7 +247,7 @@ org.eclipse.jdt.core.formatter.insert_space_after_question_in_wildcard=do not in
 org.eclipse.jdt.core.formatter.insert_space_after_semicolon_in_for=insert
 org.eclipse.jdt.core.formatter.insert_space_after_unary_operator=do not insert
 org.eclipse.jdt.core.formatter.insert_space_before_and_in_type_parameter=insert
-org.eclipse.jdt.core.formatter.insert_space_before_assignment_operator=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_assignment_operator=insert
 org.eclipse.jdt.core.formatter.insert_space_before_at_in_annotation_type_declaration=insert
 org.eclipse.jdt.core.formatter.insert_space_before_binary_operator=insert
 org.eclipse.jdt.core.formatter.insert_space_before_closing_angle_bracket_in_parameterized_type_reference=do not insert
@@ -351,7 +351,7 @@ org.eclipse.jdt.core.formatter.never_indent_line_comments_on_first_column=false
 org.eclipse.jdt.core.formatter.number_of_blank_lines_at_beginning_of_method_body=0
 org.eclipse.jdt.core.formatter.number_of_empty_lines_to_preserve=1
 org.eclipse.jdt.core.formatter.put_empty_statement_on_new_line=true
-org.eclipse.jdt.core.formatter.tabulation.char=tab
+org.eclipse.jdt.core.formatter.tabulation.char=space
 org.eclipse.jdt.core.formatter.tabulation.size=4
 org.eclipse.jdt.core.formatter.use_tabs_only_for_leading_indentations=false
 org.eclipse.jdt.core.formatter.wrap_before_binary_operator=true

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

@@ -1,37 +1,49 @@
 package org.junit.internal.runners.statements;
 
+import java.lang.management.ManagementFactory;
+import java.lang.management.ThreadMXBean;
+import java.util.Arrays;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 
+import org.junit.runners.model.MultipleFailureException;
 import org.junit.runners.model.Statement;
 
 public class FailOnTimeout extends Statement {
     private final Statement fOriginalStatement;
     private final TimeUnit fTimeUnit;
     private final long fTimeout;
+    private final boolean fLookForStuckThread;
+    private ThreadGroup fThreadGroup = null;
 
     public FailOnTimeout(Statement originalStatement, long millis) {
         this(originalStatement, millis, TimeUnit.MILLISECONDS);
     }
 
     public FailOnTimeout(Statement originalStatement, long timeout, TimeUnit unit) {
+        this(originalStatement, timeout, unit, false);
+    }
+
+    public FailOnTimeout(Statement originalStatement, long timeout, TimeUnit unit, boolean lookForStuckThread) {
         fOriginalStatement = originalStatement;
         fTimeout = timeout;
         fTimeUnit = unit;
+        fLookForStuckThread = lookForStuckThread;
     }
 
     @Override
     public void evaluate() throws Throwable {
         FutureTask<Throwable> task = new FutureTask<Throwable>(new CallableStatement());
-        Thread thread = new Thread(task, "Time-limited test");
+        fThreadGroup = new ThreadGroup("FailOnTimeoutGroup");
+        Thread thread = new Thread(fThreadGroup, task, "Time-limited test");
         thread.setDaemon(true);
         thread.start();
         Throwable throwable = getResult(task, thread);
         if (throwable != null) {
-        	throw throwable;
+            throw throwable;
         }
     }
 
@@ -55,17 +67,122 @@ private Throwable getResult(FutureTask<Throwable> task, Thread thread) {
 
     private Exception createTimeoutException(Thread thread) {
         StackTraceElement[] stackTrace = thread.getStackTrace();
-        Exception exception = new Exception(String.format(
+        final Thread stuckThread = fLookForStuckThread ? getStuckThread(thread) : null;
+        Exception currThreadException = new Exception(String.format(
                 "test timed out after %d %s", fTimeout, fTimeUnit.name().toLowerCase()));
         if (stackTrace != null) {
-            exception.setStackTrace(stackTrace);
+            currThreadException.setStackTrace(stackTrace);
             thread.interrupt();
         }
-        return exception;
+        if (stuckThread != null) {
+            Exception stuckThreadException = 
+                new Exception ("Appears to be stuck in thread " +
+                               stuckThread.getName());
+            stuckThreadException.setStackTrace(getStackTrace(stuckThread));
+            return new MultipleFailureException    
+                (Arrays.<Throwable>asList(currThreadException, stuckThreadException));
+        } else {
+            return currThreadException;
+        }
     }
 
-    private class CallableStatement implements Callable<Throwable> {
+    /**
+     * Retrieves the stack trace for a given thread.
+     * @param thread The thread whose stack is to be retrieved.
+     * @return The stack trace; returns a zero-length array if the thread has 
+     * terminated or the stack cannot be retrieved for some other reason.
+     */
+    private StackTraceElement[] getStackTrace(Thread thread) {
+        try {
+            return thread.getStackTrace();
+        } catch (SecurityException e) {
+            return new StackTraceElement[0];
+        }
+    }
 
+    /**
+     * Determines whether the test appears to be stuck in some thread other than
+     * the "main thread" (the one created to run the test).  This feature is experimental.
+     * Behavior may change after the 4.12 release in response to feedback.
+     * @param mainThread The main thread created by {@code evaluate()}
+     * @return The thread which appears to be causing the problem, if different from
+     * {@code mainThread}, or {@code null} if the main thread appears to be the
+     * problem or if the thread cannot be determined.  The return value is never equal 
+     * to {@code mainThread}.
+     */
+    private Thread getStuckThread (Thread mainThread) {
+        if (fThreadGroup == null) 
+            return null;
+        Thread[] threadsInGroup = getThreadArray(fThreadGroup);
+        if (threadsInGroup == null) 
+            return null;
+
+        // Now that we have all the threads in the test's thread group: Assume that
+        // any thread we're "stuck" in is RUNNABLE.  Look for all RUNNABLE threads. 
+        // If just one, we return that (unless it equals threadMain).  If there's more
+        // than one, pick the one that's using the most CPU time, if this feature is
+        // supported.
+        Thread stuckThread = null;
+        long maxCpuTime = 0;
+        for (Thread thread : threadsInGroup) {
+            if (thread.getState() == Thread.State.RUNNABLE) {
+                long threadCpuTime = cpuTime(thread);
+                if (stuckThread == null || threadCpuTime > maxCpuTime) {
+                    stuckThread = thread;
+                    maxCpuTime = threadCpuTime;
+                }
+            }               
+        }
+        return (stuckThread == mainThread) ? null : stuckThread;
+    }
+
+    /**
+     * Returns all active threads belonging to a thread group.  
+     * @param group The thread group.
+     * @return The active threads in the thread group.  The result should be a
+     * complete list of the active threads at some point in time.  Returns {@code null}
+     * if this cannot be determined, e.g. because new threads are being created at an
+     * extremely fast rate.
+     */
+    private Thread[] getThreadArray(ThreadGroup group) {
+        final int count = group.activeCount(); // this is just an estimate
+        int enumSize = Math.max(count * 2, 100);
+        int enumCount;
+        Thread[] threads;
+        int loopCount = 0;
+        while (true) {
+            threads = new Thread[enumSize];
+            enumCount = group.enumerate(threads);
+            if (enumCount < enumSize) break;
+            // if there are too many threads to fit into the array, enumerate's result
+            // is >= the array's length; therefore we can't trust that it returned all
+            // the threads.  Try again.
+            enumSize += 100;
+            if (++loopCount >= 5) 
+                return null;
+            // threads are proliferating too fast for us.  Bail before we get into 
+            // trouble.
+        }
+        return Arrays.copyOf(threads, enumCount);
+    }
+
+    /**
+     * Returns the CPU time used by a thread, if possible.
+     * @param thr The thread to query.
+     * @return The CPU time used by {@code thr}, or 0 if it cannot be determined.
+     */
+    private long cpuTime (Thread thr) {
+        ThreadMXBean mxBean = ManagementFactory.getThreadMXBean();
+        if (mxBean.isThreadCpuTimeSupported()) {
+            try {
+                return mxBean.getThreadCpuTime(thr.getId());
+            } catch (UnsupportedOperationException e) {
+            }
+        }
+        return 0;
+    }
+
+    private class CallableStatement implements Callable<Throwable> {
         public Throwable call() throws Exception {
             try {
                 fOriginalStatement.evaluate();
@@ -77,4 +194,4 @@ public Throwable call() throws Exception {
             return null;
         }
     }
-}
+}

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

@@ -36,6 +36,7 @@
 public class Timeout implements TestRule {
     private final long fTimeout;
     private final TimeUnit fTimeUnit;
+    private boolean fLookForStuckThread;
 
     /**
      * Create a {@code Timeout} instance with the timeout specified
@@ -66,6 +67,7 @@ public Timeout(int millis) {
     public Timeout(long timeout, TimeUnit unit) {
         fTimeout = timeout;
         fTimeUnit = unit;
+        fLookForStuckThread = false;
     }
 
     /**
@@ -84,8 +86,21 @@ public static Timeout seconds(long seconds) {
         return new Timeout(seconds, TimeUnit.SECONDS);
     }
 
+    /**
+     * Specifies whether to look for a stuck thread.  If a timeout occurs and this
+     * feature is enabled, the test will look for a thread that appears to be stuck
+     * and dump its backtrace.  This feature is experimental.  Behavior may change
+     * after the 4.12 release in response to feedback.
+     * @param enable {@code true} to enable the feature
+     * @return This object
+     * @since 4.12
+     */
+    public Timeout lookForStuckThread(boolean enable) {
+        fLookForStuckThread = enable;
+        return this;
+    }
 
     public Statement apply(Statement base, Description description) {
-        return new FailOnTimeout(base, fTimeout, fTimeUnit);
+        return new FailOnTimeout(base, fTimeout, fTimeUnit, fLookForStuckThread);
     }
 }