线程的死锁与线程的通信

产生背景

不同线程分别占用对方需要的同步资源部放弃,都在等待对方放弃自己需要的同步资源,形成了线程的死锁

解决方法

专门的算法,原则

尽量减少同步资源的定义

案例

package com.zyd.thread;

public class TestDeadLock {
    static StringBuilder sb1 = new StringBuilder();
    static StringBuilder sb2 = new StringBuilder();
    public static void main (String[] args){
            new Thread(){
              public void run(){
                  synchronized (sb1){
                      try {
                          Thread.currentThread().sleep(10);
                      } catch (InterruptedException e) {
                          e.printStackTrace();
                      }
                      sb1.append("A");
                      synchronized (sb2){
                          sb2.append("B");
                          System.out.println(sb1);
                          System.out.println(sb2);
                      }
                  }
              }
            }.start();

            new Thread(){
                public void run(){
                synchronized (sb2){
                    try {
                        Thread.currentThread().sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    sb1.append("C");
                    synchronized (sb1){
                        sb2.append("D");
                        System.out.println(sb1);
                        System.out.println(sb2);
                    }
                }
                }

            };

    }
}

线程的通信

定义在Object里面

wait():令当前线程挂起并放弃CPU,同步资源,使别的线程可访问并修改共享资源,而当前线程排队等待再次对资源的访问

notify():唤醒正在排队等待同步资源的线程中优先级最高者结束等待

notifyAll():唤醒正在排队等待资源的所有线程结束等待

注意:

这桑方法只有在synchronized方法或synchronized代码块中才能使用,否则报错

java.lang.IllegalMonitorStateException异常

案例:使用两个线程打印 1-100. 线程1, 线程2 交替打印

package com.zyd.thread;

 class PrintNum implements Runnable {
    int num = 1;
    Object obj = new Object();
    @Override
    public void run() {
        while (true){
            synchronized (obj){
                obj.notify();
                if (num <= 100){
                    try {
                        Thread.currentThread().sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName()+":"+num);
                    num++;
                }else {
                    break;
                }
                try {
                    obj.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}
public class TestCommunication{
     public static void main (String[] args){
             PrintNum p = new PrintNum();
         Thread t1 = new Thread(p);
         Thread t2 = new Thread(p);

         t1.setName("A:");
         t2.setName("B");
         t1.start();
         t2.start();
     }
}