下面方法摘录自 http://www.planetgeek.ch/2009/08/25/how-to-find-a-concurrency-bug-with-java/， 用来测试多线程并发执行的方法。

public static void assertConcurrent(final String message, final List<? extends Runnable> runnables, final int maxTimeoutSeconds) throws InterruptedException {    final int numThreads = runnables.size();    final List<Throwable> exceptions = Collections.synchronizedList(new ArrayList<Throwable>());    final ExecutorService threadPool = Executors.newFixedThreadPool(numThreads);    try {      final CountDownLatch allExecutorThreadsReady = new CountDownLatch(numThreads);      final CountDownLatch afterInitBlocker = new CountDownLatch(1);      final CountDownLatch allDone = new CountDownLatch(numThreads);      for (final Runnable submittedTestRunnable : runnables) {        threadPool.submit(new Runnable() {          public void run() {            allExecutorThreadsReady.countDown();            try {              afterInitBlocker.await();              submittedTestRunnable.run();            } catch (final Throwable e) {              exceptions.add(e);            } finally {              allDone.countDown();            }          }        });      }      // wait until all threads are ready      assertTrue("Timeout initializing threads! Perform long lasting initializations before passing runnables to assertConcurrent",           allExecutorThreadsReady.await(runnables.size() * 10, TimeUnit.MILLISECONDS));      // start all test runners      afterInitBlocker.countDown();      assertTrue(message +" timeout! More than " + maxTimeoutSeconds + " seconds", allDone.await(maxTimeoutSeconds, TimeUnit.SECONDS));    } finally {      threadPool.shutdownNow();    }    assertTrue(message + " failed with exception(s) " + exceptions, exceptions.isEmpty());  }

此方法接受三个参数：分别为错误消息， 并发执行的Runner列表，以及并发执行的超时时间。

方法中会启用一个线程池， 并将参数中的所有的Runner都准备好后并发执行runner方法， 并将所有的执行异常存放在一个list中， 如果方法在规定时间内执行完， 并且异常列表为空的情况认为方法正确执行。