CODEWITHSUNDEEP
javamultithreadingtimerexecutor
user2137817
user2137817

Reputation: 1853

Execute multiple threads each one for a certain amount of time in java

I'm sending files to my local server that creates a file back. My problem occurs when the user perform multiple actions one after another and I need to show an error message if one of the requests don't get a feedback file in 5 min.

How can I handle all these requests? I used newSingleThreadScheduledExecutor to check if the feedback file is there every minute but I don't know how to handle multiple ones and keep the countdown to each request for the 5 min case. My try:

ListeningExecutorService executor = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(listPrinter.size()));
        for(int i=0;i<list.size();i++){
            try {

                final File retrievedFile = new File("/home/"+list.get(i)+".csv");

                ListenableFuture<File> future = executor.submit(new Callable<File>() {
                    public File call() {
                        // Actually send the file to your local server
                        // and retrieve a file back

                        if(retrievedFile.exists())
                        {
                            new Notification("file exits").show(Page.getCurrent());
                        }
                        else{
                            new Notification("file no exits").show(Page.getCurrent());
                        }
                        return retrievedFile;
                    }
                });
                future.get(5, TimeUnit.MINUTES);
            } catch (InterruptedException ex) {
                Exceptions.printStackTrace(ex);
            } catch (ExecutionException ex) {
                Exceptions.printStackTrace(ex);
            } catch (TimeoutException ex) {
                Exceptions.printStackTrace(ex);
                new Notification("Time out").show(Page.getCurrent());
            }
        }

But it just get executed at the beginning and that's it but when the file is added nothing happens.

Is it possible to do this with watchService? It works pretty well for me but I didn't know about the 5 min case

Upvotes: 3

Views: 532

Answers (3)

user2137817
user2137817

Reputation: 1853

I solved the problem by using a Timer that is executed every 5 minutes getting all the db transactions that happened for the last 5 minutes and didn't get any response and show my error code. It works pretty good. Thanks everyone for the help

Upvotes: 0

fps
fps

Reputation: 34460

You could do this manually, but using Guava ListenableFuture would be much better:

// Here we create a fixed thread pool with 10 threads and an inifinite-capacity queue
ListeningExecutorService executor = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));

final File fileToSend = ...; // 

ListenableFuture<File> future = executor.submit(new Callable<File>() {
    public File call() {
        // Actually send the file to your local server
        // and retrieve a file back
        File retrievedFile = YourLocalServer.sendAndRetrieve(fileToSend);
        return retrievedFile;
    }
});

Futures.addCallback(future, new FutureCallback<File>() {

    public void onSuccess(File retrievedFile) {
        // Handle the successfully retrieved file when it returns
    }

    public void onFailure(Throwable thrown) {
        // Handle the error
    }
});

By sending the file asynchronously, you can send and retrieve many files at any given time. Then, when the server responds (either with a retrieved file or with an error), you can handle the response (retrieved file or exception) just when it comes back, without needing to wait for it. This means that the onSuccess() or onFailure() methods will be automatically executed when there's a response available from your local server.

Upvotes: 0

jjlema
jjlema

Reputation: 850

Take a look to the Future interface:

http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Future.html

should fit perfectly to your problem.

When you run a thread, the result could be a Future, it is the result of a asyncronous task, and you can have one Future per asyncronous task that you are launching.

Future<File> sendReceiveFile(File inputFile) {
    final Future<File> future = new YourFuture<File>(...);
    new Thread() {
        @Override
        public void run() {
            File outputFile = null;
            try {
                 outputFile = SendFileToServer(inputFile);
            } catch (final Exception e) {
                // do something
            } finally {
                future.setValue(fileOutput);
            }
        }
    }.start();
    return future;
}

And in your main:

Future<File> future = sendReceiveFile(myFile);
File outputFile = null;
try {
    outputFile = future.get(1, TimeUnit.MINUTE);
} catch(TimeOutException e) {
    // do something
}

Upvotes: 2

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