为什么其他条件不显示在等待线程的控制台上。如果我使用 future.get() 方法？

Question

这里是office实例getsum()returnsn位数字之和，一次只允许一个线程完成计算，休眠1秒.在此期间，其他线程将尝试锁定，如果线程未获得锁定，它会在控制台上打印 else 条件并在 do-while 循环中迭代，直到完成

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

public class Office {
    private ReentrantLock lock = new ReentrantLock(true);

    public void login(String name) {
        System.out.println("Good Morning : " + name);
    }

    public long getSum(String name, long number) {
        long sum = 0;
        try {
            do {
                if (lock.tryLock(500, TimeUnit.MILLISECONDS)) {
                    for (int i = 1; i <= number; i++) {
                        sum = sum + i;
                        Thread.sleep(1000);
                    }
                    lock.unlock();
                    break;
                } else {
                    System.out
                            .println("waiting for lock : " + name + " " + Thread.currentThread() + " " + "is waiting");
                }
            } while (true);

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return sum;
    }

    public void logout(String name) {
        System.out.println("Good night : " + name);
    }
}

import java.util.concurrent.Callable;

public class MyCallable implements Callable {
    private Office office;
    private String name;
    private long number;

    public MyCallable(Office office, String name, long number) {
        this.office = office;
        this.name = name;
        this.number = number;
    }

    @Override
    public Object call() throws Exception {
        office.login(name);
        long total = office.getSum(name, number);
        office.logout(name);
        return total + " " + name;
    }
}

这里future.get()如果我们正在使用，我们无法通过控制台获取线程等待语句，如果我们不是，则等待语句成功显示在控制台.我有点好奇为什么它会发生，因为 get() 仅在 Thread 完成时显示结果，并在必要时等待计算完成，然后检索其结果。它如何影响 office 实例

的 getSum 中的 else 语句

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class Main {
    public static void main(String[] args) {
        long total = 0;
        String name = null;
        Office office = new Office();
        MyCallable myCallable[] = { new MyCallable(office, "Nik", 10), new MyCallable(office, "Dev", 20),
                new MyCallable(office, "push", 30), new MyCallable(office, "Sam", 40) };

        ExecutorService service = Executors.newFixedThreadPool(2);
        for (MyCallable callable : myCallable) {

            Future future = service.submit(callable);
            try {
                String result[] = future.get().toString().split(" ");
                total = Integer.parseInt((result[0]));
                name = result[1];
                System.out.println(name + " " + total);
            } catch (InterruptedException | ExecutionException e) {
                e.printStackTrace();
            }

        }
        service.shutdown();
    }
}

我使用 future.get() 方法

OUTPUT:
Good Morning : Nik
Good night : Nik
Nik 55
Good Morning : Dev
Good night : Dev
Dev 210
Good Morning : push
Good night : push
push 465
Good Morning : Sam
Good night : Sam
Sam 820

这里我期待 else 语句也用于等待线程，但如果我使用 future.get();

则不会得到它

Answer 1

您需要先提交所有期货，然后才尝试调用.get()。这是您修改的主要方法：

    public static void main(String[] args) {
        long total = 0;
        String name = null;
        Office office = new Office();
        MyCallable myCallable[] = { 
                new MyCallable(office, "Nik", 10), 
                new MyCallable(office, "Dev", 20),
                new MyCallable(office, "push", 30), 
                new MyCallable(office, "Sam", 40) };

        ExecutorService service = Executors. newFixedThreadPool(2);
        List<Future> futures = new ArrayList<>();
        for (MyCallable callable : myCallable) {
            futures.add(service.submit(callable));
        }
        for (Future future : futures) {
            try {
                String result[] = future.get().toString().split(" ");
                total = Integer.parseInt((result[0]));
                name = result[1];
                System.out.println(name + " " + total);
            } catch (InterruptedException | ExecutionException e) {
                e.printStackTrace();
            }
        }
        service.shutdown();
    }

这会产生以下输出：

Good Morning : Dev
Good Morning : push
waiting for lock : Dev Thread[pool-1-thread-2,5,main] is waiting
waiting for lock : Dev Thread[pool-1-thread-2,5,main] is waiting

为什么其他条件不显示在等待线程的控制台上。如果我使用 future.get() 方法？

Why else condition not shows over console for waiting Thread. if i'm using future.get() method?

java

multithreading

callable

thread-synchronization

reentrantlock