[JAVA] Item 80: Prefer executors, tasks, and streams to threads

80. Select executors, tasks, and streams from threads

• You can easily execute the process in the background using the Executor Framework.
• By using the Executor Framework, it is now possible to wait until all tasks are completed, or wait until any one task is completed, execute tasks periodically, and so on.

package tryAny.effectiveJava;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ExecutorTest {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        List<Callable<String>> tasks = Arrays.asList(() -> "first", () -> "second");

        ExecutorService es = Executors.newFixedThreadPool(2);
        List<Future<String>> rets = es.invokeAll(tasks);

        for (Future<String> r : rets) {
            System.out.println(r.get());
        }

        System.out.println(es.invokeAny(tasks));//first or second randomly

    }
}

package tryAny.concurrentUtility;

import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

//Continues to generate random values every second.
public class ConcurrentTest6 {
    public static void main(String[] args) {
	ScheduledThreadPoolExecutor stpe = new ScheduledThreadPoolExecutor(1);

	ScheduledFuture<?> sf = stpe.scheduleAtFixedRate(new Runnable() {
	    @Override
	    public void run() {
		System.out.println(Math.random());
	    }
	}, 1000, 1000, TimeUnit.MILLISECONDS);

	while (true) {
	    if (sf.isCancelled() || sf.isDone()) {
		stpe.shutdown();
		break;
	    }
	}
    }
}

• If you want to process using multiple threads, use java.util.concurrent.Executors because there is a factory method to create various thread pools. If their use does not suit your needs, use ThreadPoolExecutor directly.
• NewCachedThreadPool can be used on a server with relatively light processing, but cached thread pool behaves like executing a submitted task immediately and creating a new thread if there is no thread, so on a server with heavy processing You should use newFixedThreadPool.
• Avoid using Threads directly. In ExecutorFramework, the unit of processing and the mechanism of execution are separated, and there is flexibility.
• Since Java7, it has become possible to execute processing efficiently with a mechanism called fork-join.

package tryAny.concurrentUtility;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;

public class ConcurrentTest8 {
    public static void main(String[] args) {
        int data[] = { 1, 2, 3, 4, 5, 6, 7 };
        ForkJoinPool service = new ForkJoinPool();
        service.invoke(new AddAction(data, 0, data.length));
    }
}

class AddAction extends RecursiveAction {
    private static final int THRESHOLD_SIZE = 3;
    private int start;
    private int end;
    private int[] numbers;

    public AddAction(int[] numbers, int start, int end) {
        this.start = start;
        this.end = end;
        this.numbers = numbers;
    }

    protected void compute() {
        int total = 0;
        if (end - start <= THRESHOLD_SIZE) {
            for (int i = start; i < end; i++) {
                total += numbers[i];
            }
            System.out.println(total + " ");
        } else {
            new AddAction(numbers, start + THRESHOLD_SIZE, end).fork();
            new AddAction(numbers, start, Math.min(end, start + THRESHOLD_SIZE)).compute();
        }
    }
}