Question

线程t1在wait()被击中后进入死锁状态。即使 t2中有notify()。代码陷入僵局。没有得到Print语句 - “等待被释放后::::”

我可以看到两个线程竞争在counterAdd()中获取监视器。因此，我认为通知将起作用。

package com.java.thread.practice;

  public class WaitAndNotify4 {

        int counter = 0;

        /*
           CounterAdd() is to be accessed by both t1 and t2.
           If not synchronized not giving consistent output. 
        */ 
        synchronized int counterAdd(){
            return counter++;
        }

        public static void main(String[] args) throws InterruptedException{

            // Creating method to call the threads.
            WaitAndNotify4 andNotify4 = new WaitAndNotify4();
            andNotify4.testRaceCondition();

        }

        private  void testRaceCondition() throws InterruptedException {

            // Thread t1 created and launched.

            Thread t1 = new Thread(new Runnable(){
                @Override
                public void run() {

                    for(int i=0; i<5; i++){
                        synchronized(this){
                        if(i== 1){
                            System.out.println("Calling wait after count 1");
                            try {
                             // Assuming that this wait will be resumed by notify in t2.

                                wait();
                                System.out.println("After wait is released :::: ");
                            } catch (InterruptedException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }

                        }
                        }
                        counterAdd();
                    }
                }
            });


            Thread t2 = new Thread(new Runnable(){
                @Override
                public void run() {
                    // TODO Auto-generated method stub

                    for(int i=0; i<5; i++){
                        if(i==2){

                            synchronized(this){
                                System.out.println("Before releasing the counter :::::");
                                notify();
                                System.out.println("After releasing the counter :::::");
                            }

                        }
                        counterAdd();
                    }

                }
            });



            t1.start();
            t2.start();

            t1.join();
            t2.join();

            System.out.println(" Sum value is found as ::::: "+counter);

        }
    }

Answer 1

您正在同步不同的对象。对象t1的第一种情况，t2的第二种情况，counterAdd上的方法andNotify4。为了锁定andNotify4，你需要做任何类似的事情。

public class Main {
    private int counter = 0;

    synchronized int counterAdd() {
        return counter++;
    }

    public static void main(String[] args) throws InterruptedException {
        Main andNotify4 = new Main();
        andNotify4.testRaceCondition();
    }

    private void testRaceCondition() throws InterruptedException {
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 5; i++) {
                    synchronized (Main.this) {
                        if (i == 1) {
                            System.out.println("Calling wait after count 1");
                            try {
                                Main.this.wait();
                                System.out.println("After wait is released :::: ");
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                    counterAdd();
                }
            }
        });

        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 5; i++) {
                    if (i == 2) {
                        synchronized (Main.this) {
                            System.out.println("Before releasing the counter :::::");
                            Main.this.notify();
                            System.out.println("After releasing the counter :::::");
                        }
                    }
                    counterAdd();
                }
            }
        });

        t1.start();
        t2.start();

        t1.join();
        t2.join();

        System.out.println(" Sum value is found as ::::: " + counter);
    }
}

等待并通知Java中的死锁情况

1 个答案: