I am learning to use ExectorService to pool threads and send out tasks. I have a simple program below
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
class Processor implements Runnable {
private int id;
public Processor(int id) {
this.id = id;
}
public void run() {
System.out.println("Starting: " + id);
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
System.out.println("sorry, being interupted, good bye!");
System.out.println("Interrupted " + Thread.currentThread().getName());
e.printStackTrace();
}
System.out.println("Completed: " + id);
}
}
public class ExecutorExample {
public static void main(String[] args) {
Boolean isCompleted = false;
ExecutorService executor = Executors.newFixedThreadPool(2);
for (int i = 0; i < 5; i++) {
executor.execute(new Processor(i));
}
//executor does not accept any more tasks but the submitted tasks continue
executor.shutdown();
System.out.println("All tasks submitted.");
try {
//wait for the exectutor to terminate normally, which will return true
//if timeout happens, returns false, but this does NOT interrupt the threads
isCompleted = executor.awaitTermination(100, TimeUnit.SECONDS);
//this will interrupt thread it manages. catch the interrupted exception in the threads
//If not, threads will run forever and executor will never be able to shutdown.
executor.shutdownNow();
} catch (InterruptedException e) {
}
if (isCompleted) {
System.out.println("All tasks completed.");
} else {
System.out.println("Timeout " + Thread.currentThread().getName());
}
}
}
It does nothing fancy, but creates two threads and submits 5 tasks in total. After each thread completes its task, it takes the next one,
In the code above, I use executor.submit. I also changed to executor.execute. But I do not see any difference in the output. In what way are the submit and execute methods different?
This what the API says
Method submit extends base method Executor.execute(java.lang.Runnable) by creating and returning a Future that can be used to cancel execution and/or wait for completion. Methods invokeAny and invokeAll perform the most commonly useful forms of bulk execution, executing a collection of tasks and then waiting for at least one, or all, to complete. (Class ExecutorCompletionService can be used to write customized variants of these methods.)
But it's not clear to me as what it exactly means?
