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POIs this an Improper use of CountdownLatch with initial count = 1
 

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    <p>Below is the snippet, listing 5.11 from book 'java concurrency in practice' by Brain Goetz.</p> <p>I find the below code confusing. It seems that countdownlatch 'startGate' has a flawed usage. ( 'endGate' usage is OK )</p> <pre><code>public class TestHarness { public long timeTasks(int nThreads, final Runnable task) throws InterruptedException { final CountDownLatch startGate = new CountDownLatch(1); final CountDownLatch endGate = new CountDownLatch(nThreads); for (int i = 0; i &lt; nThreads; i++) { Thread t = new Thread() { public void run() { try { startGate.await(); try { task.run(); } finally { endGate.countDown(); } } catch (InterruptedException ignored) { } } }; t.start(); } long start = System.nanoTime(); startGate.countDown(); endGate.await(); long end = System.nanoTime(); return end - start; } </code></pre> <p>}</p> <p>Execution of line <code>startGate.countDown()</code> will notify all the worker threads waiting on the latch. But is this guaranteed to notify all the nThreads ?<br/> It is quite possible only a few threads, say 2 threads, out nTheads have executed startGate.await() call of the run() method. <br/> And at this time the main thread executes <code>startGate.countDown()</code>. This call will notify only the 2 threads ( out of nThreads ) waiting on the latch. <br/></p> <p>Now the rest of the other threads ( nThread - 2 ) will call <code>startGate.await()</code> later in time, but as the main thread has already raised a notification, so the worker threads( nThreads- 2) will now wait indefinitely for notification ?</p> <p>Or I am missing something ?</p>
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