多线程通信 wait和notify

Love The Way You Lie 2023-08-17 17:33 126阅读 0赞

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();
    	}
    	
    	
    }