Re: How to stop Java HTTP server

From:
Shiladitya <shiladitya.biswas@gmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 14 Oct 2010 10:16:35 -0700 (PDT)
Message-ID:
<0c2e3506-ea34-4eb9-87db-62440bc07e25@c32g2000vbq.googlegroups.com>
On Oct 14, 8:12 am, Tom Anderson <t...@urchin.earth.li> wrote:

On Wed, 13 Oct 2010, Shiladitya wrote:

I need a way to call httpServerExe.stop() from this thread.

So the main thread can be like this:

      httpServerExe.start();
      while(!terminated) {
         Thread.sleep(4000);
        }
        httpServerExe.stop();


That's the wrong way to do it. Rather than sleeping in a loop, this threa=

d

should wait on a monitor, and threads which want to stop the server shoul=

d

notify that monitor.

The main code would look like:

server.start();
synchronized (terminationLock) {
        while (!terminated) terminationLock.wait();}

server.stop();

Code which wants to stop it can go:

terminated = true;
synchronized (terminationLock) {
        terminationLock.notify();

}

I have set up a handler for a URL (/terminateCommand). So if anyone sen=

d

a request to this URL, the terminated flag should be set and main threa=

d

should stop the http server.

But I can't figure out how to set the flag from one of the handlers so
that main thread gets interrupted.


The handler has to have a reference to the place the flag lives. If the
flag is a static variable on a class, then it can go directly to the clas=

s

by name:

MainClass.terminated = true;
synchronized (terminationLock) {
        MainClass.terminationLock.notify();

}

Although of course it would be better to wrap that in a method:

MainClass.terminate();

class MainClass {
        private static boolean terminated;
        private static Object terminationLock;
        public static void terminate() {
                terminated = true;
                synchronized (terminationLock) {
                        terminationLock.notify();
                }
        }

}

If it's on an object, then you will need to pass a reference to that
object to the handler somehow, perhaps when you construct it.

void main(String... args) {
        HttpServer server = HttpServer.create();
        ServerController controller = new ServerController(serv=

er);

        HttpHandler terminationHandler = new TerminationHandler=

(controller);

        server.createContext("/terminate", terminationHandler);
        new Thread(controller).start;

}

class ServerController implements Runnable {
        private HttpServer server;
        private boolean terminated;
        private Object terminationLock = new Object();
        public ServerController(HttpServer server) {
                this.server = server;
        }
        public void run() {
                server.start();
                synchronized (terminationLock) {
                        try {
                                while (!t=

erminated) terminationLock.wait();

                        }
                        catch (InterruptedExcepti=

on e) {}

                }
                server.stop();
        }
        public void terminate() {
                terminated = true;
                synchronized (terminationLock) {
                        terminationLock.notify();
                }
        }

}

You could dispense with the terminationLock by using the ServerController
itself to wait and notify on, but i tend to steer way from that, and use
private objects as locks, so that the wait/notify activity of the methods
can't 'leak' across the interface.

An even better way to do this, actually, would be with a
java.util.concurrent.CountDownLatch with a count of one:

class ServerController implements Runnable {
        private HttpServer server;
        private CountDownLatch latch = new CountDownLatch(1);
        public ServerController(HttpServer server) {
                this.server = server;
        }
        public void run() {
                server.start();
                try {
                        latch.await();
                }
                catch (InterruptedException e) {}
                server.stop();
        }
        public void terminate() {
                latch.countDown();
        }

}

tom

--
you can't feel your stomack with glory -- Czako


That was very helpful Tom. I have tested it out and it works nicely !

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