i am currently learning to use the the concurrent features of Java provided by the package java.util.concurrent. As an exercise i tried to write a little program that could be used to performance test a HTTP API. But somehow my program is not terminating correctly very often. It even crashes my OS.
Following is the pseudo code of my program:
- Instantiate Request Objects, that query an HTTP API (In the example i just query one random site).
- Instantiate multiple Callables, where each one represents a represents an Http Call.
- Iterate over the Callables and schedule them via a ScheduledExecutorService (how many requests should be performed per second can be configured at the begin of the code).
- After scheduling all Callables, i am beginning to iterate over the Futures. If a futures is done, retrieve the response. Do this every second. If no new Future was finished, quit the loop.
What problems am i experiencing in detail?
- Lots of times, the program is not finishing correctly. I see all log prints in the console, as if the program is finishing correctly. But actually i am seeing that stop button in eclipse still remains active
. If i click it, it says that the program could not be terminated correctly. It does not finish no matter how i long i wait (NOTE: I am starting the program inside eclipse). - I can provoke the error easily if i am increasing the number of Requests. If am turning up to 2000, this will happen for sure. If it happens my OS even crashes, i can still use eclipse, but other apps do not work anymore.
- My Environment is Eclipse 3.7 on Mac OS X 10.7 with Java 1.6 and Apache httpclient 4.2.2
Do you spot any major erros in my code? Before i have never had such issues in a java program with crashing my OS and seeing no exceptions at all.
The code:
public class ConcurrentHttpRequestsTest {
/**
* @param args
*/
public static void main(String[] args) {
ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(25);
Integer standardTimeout = 5000;
Float numberOfRequestsPerSecond = 50.0f;
Integer numberOfRequests = 500;
Integer durationBetweenRequests = Math.round(1000 / numberOfRequestsPerSecond);
// build Http Request
HttpGet request = null;
request = new HttpGet("http://www.spiegel.de");
// request.addHeader("Accept", "application/json");
HttpParams params = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(params, standardTimeout);
HttpConnectionParams.setSoTimeout(params, standardTimeout);
request.setParams(params);
// setup concurrency logic
Collection<Callable<Long>> callables = new LinkedList<Callable<Long>>();
for (int i = 1; i <= numberOfRequests; i++) {
HttpClient client = new DefaultHttpClient();
callables.add(new UriCallable(request, client));
}
// start performing requests
int i = 1;
Collection<Future<Long>> futures = new LinkedList<Future<Long>>();
for (Callable<Long> callable : callables) {
ScheduledFuture<Long> future = scheduledExecutorService.schedule(callable, i * durationBetweenRequests, TimeUnit.MILLISECONDS);
futures.add(future);
i++;
}
// process futures (check wether they are ready yet)
Integer maximumNoChangeCount = 5;
boolean futuresAreReady = false;
int noChangeCount = 0;
int errorCount = 0;
List<Long> responses = new LinkedList<Long>();
while (!futuresAreReady) {
boolean allFuturesAreDone = true;
boolean atLeast1FutureIsDone = false;
Iterator<Future<Long>> iterator = futures.iterator();
while (iterator.hasNext()) {
Future<Long> future = iterator.next();
allFuturesAreDone = allFuturesAreDone && (future.isDone());
if (future.isDone()) {
try {
atLeast1FutureIsDone = true;
responses.add(future.get());
iterator.remove();
} catch (Exception e) {
// remove failed futures (e.g. timeout)
// System.out.println("Reached catch of future.get()" +
// e.getClass() + " " + e.getCause().getClass() + " " +
// e.getMessage());
iterator.remove();
errorCount++;
}
}
if (future.isCancelled()) {
// this code is never reached. Just here to make sure that
// this is not the cause of problems.
System.out.println("Found a cancelled future. Will remove it.");
iterator.remove();
}
}
if (!atLeast1FutureIsDone) {
System.out.println("At least 1 future was not done. Current noChangeCount:" + noChangeCount);
noChangeCount++;
} else {
// reset noChangeCount
noChangeCount = 0;
}
futuresAreReady = allFuturesAreDone;
// log the current state of responses, errors and remaining futures
System.out.println("Size of responses :" + responses.size() + "; Size of futures:" + futures.size() + " Errors:" + errorCount);
if (noChangeCount >= maximumNoChangeCount) {
System.out.println("Breaking while loop becauce no new future finished in the last " + maximumNoChangeCount + " iterations");
break;
}
// check every second
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (Long responsetime : responses) {
// analyze responsetimes or whatever
}
// clean up
// .shutdown() made even more problems than shutdownNow()
scheduledExecutorService.shutdownNow();
System.out.println("Executors have been shutdown - Main Method finished. Will exit System.");
System.out.flush();
System.exit(0);
}
private static class UriCallable implements Callable<Long> {
private HttpUriRequest request;
private HttpClient client;
public UriCallable(HttpUriRequest request, HttpClient client) {
super();
this.request = request;
this.client = client;
}
public Long call() throws Exception {
Long start = System.currentTimeMillis();
HttpResponse httpResponse = client.execute(request);
Long end = System.currentTimeMillis();
return end - start;
}
}
}
