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POThreads in newCachedThreadPool() are always waiting and the thread count is always increasing
 

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  1. POThreads in newCachedThreadPool() are always waiting and the thread count is always increasing
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    <p>I meet a problem that tomcat throws <code>OutOfMemoryError</code>:</p> <pre><code>SEVERE: Servlet.service() for servlet DataPortServlet threw exception java.lang.OutOfMemoryError: unable to create new native thread at java.lang.Thread.start0(Native Method) at java.lang.Thread.start(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.addIfUnderMaximumPoolSize(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.execute(Unknown Source) at java.util.concurrent.AbstractExecutorService.submit(Unknown Source) ... </code></pre> <p>What I want to do is: when data received in a servlet, send the received data to another server through <code>HttpClient</code>, related code:</p> <p>servlet:</p> <pre><code>protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException { ... byte[] data = getDataFromRequest(request); // pseudo code, get data CallableLogSender sender = new CallableLogSender(data); pool.submit(sender); // here the pool is the one instantiated at the start of application, singleton ... } </code></pre> <p>class implements <code>Callable</code> interface:</p> <pre><code>public class CallableLogSender implements Callable&lt;Integer&gt; { private byte[] content; public CallableLogSender(byte[] content) { this.content = content; } @Override public Integer call() { try { String uri = getRemoteServerUri(); // pseudo code, get uri here HttpPost request = new HttpPost(uri); request.setHeader("Content-Type", "application/x-www-form-urlencoded"); request.setEntity(new ByteArrayEntity(content)); HttpClient httpClient = getHttpClient(); // pseudo code, get cached http client, it is a singleton instance HttpResponse response = httpClient.execute(request); statusCode = response.getStatusLine().getStatusCode(); EntityUtils.consume(response.getEntity()); } catch(Exception e) { // log error here... } finally { request.releaseConnection(); } return statusCode; } } </code></pre> <p>As shown in the code, I <code>submit</code> a task to thread pool every time when a client connected, then I use jProfiler to monitor tomcat, it shows that the thread number in the pool is always increasing!!! and all the threads are in <code>waiting</code> state, so when the thread number exceeds the threshold, <code>OutOfMemoryError</code> occurs.</p> <p>In my opinion, the threads should be reused and the thread number should be stable, at least not always increase, I don't know if it is because the <code>waiting</code> state makes the pool think that the threads are all "busy", so new thread needs to be created.</p> <p>So any suggestion about how to make the pool reuse the threads and not always create new thread?</p> <p>Thanks in Advance, Kelvin</p> <hr> <p>edit: Finally I find the root cause is because the http request takes too long to respond, so if tasks are submitted in a burst, the thread count will be always increasing, since one task takes too long to complete.</p>
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    1. USKelvin Hu
    1. USKelvin Hu
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      1. POThreads in newCachedThreadPool() are always waiting and the thread count is always increasing
      1. USNicholas
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    1. COHow do you instantiate your pool, and have you tried naming your threads such that you can identify if it's the pool threads *in particular* consuming resources ?
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      1. POThreads in newCachedThreadPool() are always waiting and the thread count is always increasing
      1. USBrian Agnew
    2. CO@BrianAgnew The pool is instantiated at the start of the application, so it is a singleton. I did not name my threads, but the pool did it, from jProfiler I see their names are all like `pool-2-thread-1842`, the last integer varies.
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      1. POThreads in newCachedThreadPool() are always waiting and the thread count is always increasing
      1. USKelvin Hu
 

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