java - 递增变量多线程

Question

假设我有 10 个线程将变量递增 1。假设线程 1 首先递增变量，然后线程 2 和线程 3 依次递增。在所有 10 个线程都递增了变量之后。我需要以某种方式减少同一个变量。

递减，如果 Thread-1 首先递增变量，那么它应该最后递减。

我们需要在不设置线程优先级的情况下执行此操作。

Answer 1

您可以使用多种方法，以下是一个示例:

public class Main {
    public static void main(String[] args) throws Exception {
        for(int i=0;i<10;i++){
            final int _i=i;
            Thread t = new Thread(new T(_i));
            t.start();
      }
    }
    public static class T implements Runnable{
        int threadNumber;
        public T(int threadNumber) {
            this.threadNumber=threadNumber;
        }

        @Override
        public void run() {
            increase(this);
        }
    }
    static Thread[] threads = new Thread[10];
    static int number  =0;
    static Object generalLock=new Object();
    public static void increase(T t){
        int myNumber=0;
        synchronized (generalLock){
            myNumber=number;
            System.out.println("i am "+number+" incrementing, my real number "+t.threadNumber);
            threads[number]=Thread.currentThread();
            number++;
        }
        while (threads[9]==null){
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        for(int i=9;i>myNumber;i--){
            try {
                threads[i].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        synchronized (generalLock){
            System.out.println("i am "+number+" decrementing, my real number "+t.threadNumber);
            number--;
        }
    }
}

输出示例:

i am 0 incrementing, my real number 1
i am 1 incrementing, my real number 8
i am 2 incrementing, my real number 9
i am 3 incrementing, my real number 7
i am 4 incrementing, my real number 6
i am 5 incrementing, my real number 5
i am 6 incrementing, my real number 0
i am 7 incrementing, my real number 4
i am 8 incrementing, my real number 3
i am 9 incrementing, my real number 2
i am 9 decrementing, my real number 2
i am 8 decrementing, my real number 3
i am 7 decrementing, my real number 4
i am 6 decrementing, my real number 0
i am 5 decrementing, my real number 5
i am 4 decrementing, my real number 6
i am 3 decrementing, my real number 7
i am 2 decrementing, my real number 9
i am 1 decrementing, my real number 8
i am 0 decrementing, my real number 1

注意:您可以使用简单的 Runnable，我创建了 T 类来显示线程号，以便在递增/递减时打印它