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FuturesA.java Simple example of using Futures.
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class FuturesA {
public static void run() throws Exception {
ExecutorService executor = new ThreadPoolExecutor(4, 4, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<Runnable>());
Future<String> f1 = executor.submit(new CallToRemoteServiceA());
Future<String> f2 = executor.submit(new CallToRemoteServiceB());
System.out.println(f1.get() + " - " + f2.get());
}
public static void main(String args[]) {
try {
run();
} catch (Exception e) {
e.printStackTrace();
}
}
private static final class CallToRemoteServiceA implements Callable<String> {
@Override
public String call() throws Exception {
// simulate fetching data from remote service
Thread.sleep(100);
return "responseA";
}
}
private static final class CallToRemoteServiceB implements Callable<String> {
@Override
public String call() throws Exception {
// simulate fetching data from remote service
Thread.sleep(40);
return "responseB";
}
}
}

Will you consider add those after the io?

    executor.shutdown();
    executor.awaitTermination(100, TimeUnit.MILLISECONDS);
@ghost

ghost commented Oct 19, 2014

The expected output is that System.out.println(f1.get() + " - " + f2.get());
will take 140 ms to return?

No, both future will start in parallel. It will take less than (100+40) ms.

mabh commented Sep 28, 2015

expression in sysout will take approximately 100ms to get evaluated

It will take 140ms approximately if there is single core, otherwise it will do 100ms

amitp85 commented Aug 2, 2017 edited

@limxtop1989 It will not take 140ms on single core because both threads can sleep in parallel, it will not wait for one thread's sleep to finish before executing another thread.

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