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Implement destroy() method for graceful shutdown of MetricsStreamServlet #128

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merged 1 commit into from
Mar 20, 2013
+20 −1
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Implement destroy() method for graceful shutdown of MetricsStreamServlet #128

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21 changes: 20 additions & 1 deletion ...ain/java/com/netflix/hystrix/contrib/metrics/eventstream/HystrixMetricsStreamServlet.java
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Original file line number Diff line number Diff line change
Expand Up @@ -64,13 +64,25 @@ public class HystrixMetricsStreamServlet extends HttpServlet {
private static AtomicInteger concurrentConnections = new AtomicInteger(0);
private static DynamicIntProperty maxConcurrentConnections = DynamicPropertyFactory.getInstance().getIntProperty("hystrix.stream.maxConcurrentConnections", 5);

private volatile boolean isDestroyed = false;

/**
* Handle incoming GETs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
handleRequest(request, response);
}

/**
* Handle servlet being undeployed by gracefully releasing connections so poller threads stop.
*/
@Override
public void destroy() {
/* set marker so the loops can break out */
isDestroyed = true;
super.destroy();
}

/**
* - maintain an open connection with the client
Expand Down Expand Up @@ -115,7 +127,7 @@ private void handleRequest(HttpServletRequest request, HttpServletResponse respo
// we will use a "single-writer" approach where the Servlet thread does all the writing
// by fetching JSON messages from the MetricJsonListener to write them to the output
try {
while (poller.isRunning()) {
while (poller.isRunning() && !isDestroyed) {
List<String> jsonMessages = jsonListener.getJsonMetrics();
if (jsonMessages.isEmpty()) {
// https://github.com/Netflix/Hystrix/issues/85 hystrix.stream holds connection open if no metrics
Expand All @@ -126,8 +138,15 @@ private void handleRequest(HttpServletRequest request, HttpServletResponse respo
response.getWriter().println("data: " + json + "\n");
}
}

/* shortcut breaking out of loop if we have been destroyed */
if(isDestroyed) {
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Is this if really necessary?

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No it's not. I put it there just so destroying wouldn't potentially wait for the Thread.sleep but that's generally 500ms to maybe 2000ms - but someone could theoretically inject a very long delay. That's the only edge case this doesn't gracefully handle (someone putting in a 10000ms delay for example) since we don't interrupt the threads (and we don't track them all) but I don't know that this edge case is a big concern.

Short answer - probably not worth the optimization.

break;
}

// after outputting all the messages we will flush the stream
response.flushBuffer();

// now wait the 'delay' time
Thread.sleep(delay);
}
Expand Down