多线程通信 wait和notify-蒲公英云

多线程通信 wait和notify

一、概念
线程是操作系统中独立的个体，这些线程如果不通过特殊的手段进行处理，就无法组成一个完整的整体。因此线程通信就称为组成一个整体的必须条件之一。当线程之间存在通信，那么系统之间的交互就会更加强大。在提高CPU使用率的前提下，会使开发人员对线程任务在开发的过程中进行有效的把控和监督。
使用wait/notify实现线程之间的通信。这两个方法都是Object的类方法。也就是java的所有对象都提供了这两个方法。
wait/notify必须配合关键字synchronize使用
wait方法是释放锁，notify方法是不释放锁
1.异步通信

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
public class ListAdd2 { 
    private volatile static List list = new ArrayList();    
    public void add(){ 
        list.add("bjsxt");
    }
    public int size(){ 
        return list.size();
    }
    public static void main(String[] args) { 
        final ListAdd2 list2 = new ListAdd2();
        final Object lock = new Object();
        Thread t1 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                try { 
                    synchronized (lock) { 
                        System.out.println("t1启动..");
                        for(int i = 0; i <10; i++){ 
                            list2.add();
                            System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
                            Thread.sleep(500);
                            if(list2.size() == 5){ 
                                System.out.println("已经发出通知..");
                                lock.notify();
                            }
                        }                        
                    }
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
        }, "t1");
        Thread t2 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                synchronized (lock) { 
                    System.out.println("t2启动..");
                    if(list2.size() != 5){ 
                        try { 
                            lock.wait();
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                    System.out.println("当前线程：" + Thread.currentThread().getName() + "收到通知线程停止..");
                    throw new RuntimeException();
                }
            }
        }, "t2");    
        t2.start(); // 注意此处，t2线程先启动
        t1.start();
    }
}

2.实时通信

public class ListAdd3 { 
    private volatile static List list = new ArrayList();
    final static CountDownLatch countDownLatch = new CountDownLatch(1);  // 数字表示发起几次通知，线程才会被唤醒，如果为2，则需要写两次通知，如代码中注释
    public void add(){ 
        list.add("bjsxt");
    }
    public int size(){ 
        return list.size();
    }
    public static void main(String[] args) { 
        final ListAdd3 list2 = new ListAdd3();
        final Object lock = new Object();
        Thread t1 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                try { 
                  // synchronized (lock) { 
                        System.out.println("t1启动..");
                        for(int i = 0; i <10; i++){ 
                            list2.add();
                            System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
                            Thread.sleep(500);
                            if(list2.size() == 5){ 
                                System.out.println("已经发出通知..");
                                countDownLatch.countDown();
                                //countDownLatch.countDown(); // 如果括号中数字为2，则这里写几次
                               // lock.notify();
                            }
                        }
                   // }
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
        }, "t1");
        Thread t2 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                //synchronized (lock) { 
                    System.out.println("t2启动..");
                    if(list2.size() != 5){ 
                        try { 
                            //lock.wait();
                            countDownLatch.await();
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                    System.out.println("当前线程：" + Thread.currentThread().getName() + "收到通知线程停止..");
                    throw new RuntimeException();
                }
           // }
        }, "t2");
        t2.start();
        t1.start();
    }
}
import java.util.ArrayList;
import java.util.List;
public class ListAdd1 { 
    private volatile static List list = new ArrayList();    
    public void add(){ 
        list.add("bjsxt");
    }
    public int size(){ 
        return list.size();
    }
    public static void main(String[] args) { 
        final ListAdd1 list1 = new ListAdd1();
        Thread t1 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                try { 
                    for(int i = 0; i <10; i++){ 
                        list1.add();
                        System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
                        Thread.sleep(500);
                    }    
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
        }, "t1");
        Thread t2 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                while(true){ 
                    if(list1.size() == 5){ 
                        System.out.println("当前线程收到通知：" + Thread.currentThread().getName() + " list size = 5 线程停止..");
                        throw new RuntimeException();
                    }
                }
            }
        }, "t2");        
        t1.start();
        t2.start();
    }
}