Java并发编程---使用wait/notify模拟阻塞Queue

深碍√TFBOYSˉ_ 2022-06-02 00:27 148阅读 0赞

**一.BlockingQueue(阻塞Queue)**

**1.概念**

顾名思义,首先它是一个队列,并且支持阻塞的机制,阻塞地放入和得到数据.我们要实现LinkedBlockingQueue下面两个简单的方法put和take

put(anObject):把anObject加到BlockingQueue里,如果BlockingQueue没有空间,则调用此方法的线程被阻断,直到BlockingQueue里面有空间再继续

take:取走BlockingQueue里排在首位的对象,若BlockingQueue为空,阻断进入等待状态,直到BlockingQueue有新的数据被加入

**2.代码示例**

package com.thread.message;
    
    import java.util.LinkedList;
    import java.util.concurrent.TimeUnit;
    import java.util.concurrent.atomic.AtomicInteger;
    
    public class MyQueue {
    	//1.需要一个承载元素的集合
    	LinkedList<Object> list = new LinkedList<Object>();
    	
    	//2.需要一个计数器(统计linkedList的个数)
    	private AtomicInteger count = new AtomicInteger(0);
    	
    	//3.需要制约上限和下限
    	private final int minSize = 0;
    	private int maxSize;
    	
    	//4.构造方法
    	public MyQueue(int size) {
    		this.maxSize = maxSize;
    	}
    
    	//5.初始化一个对象,用于加锁
    	private final Object lock = new Object();
    	
    	//put(anObject):把anObject加到BlockingQueue里,如果BlockingQueue没有空间,则调用此方法的线程被阻断,直到BlockingQueue里面有空间再继续
    	public void put(Object obj){
    		synchronized (lock) {
    			while(count.get() == this.maxSize){
    				try {
    					lock.wait();
    				} catch (InterruptedException e) {
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    			}
    			//1.加入元素
    			list.add(obj);
    			//2.计数器累加
    			count.incrementAndGet();    //加1后notify
    			//通知另外一个线程(唤醒)
    			lock.notify();
    			System.out.println("新加入的元素为: " + obj);
    		}
    	}
    	
    	//take: 取走BlockingQueue里排在首位的对象,若BlockingQueue为空,阻断进入等待状态,直到BlockingQueue有新的数据被加入
    	public Object take(){
    		Object ret = null;
    		synchronized (lock) {
    			while(count.get() == this.maxSize){
    				try {
    					lock.wait();
    				} catch (InterruptedException e) {
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    			}
    			//1.做移除元素操作
    			ret = list.removeFirst();
    			//2.计数器递减
    			count.decrementAndGet();
    			//3.唤醒另外一个线程
    			lock.notify();
    		}
    		return ret;
    	}
    	
    	public int getSize(){
    		return this.count.get();
    	}
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		final MyQueue mq = new MyQueue(5);
    		mq.put("a");
    		mq.put("b");
    		mq.put("c");
    		mq.put("d");
    		mq.put("e");
    		
    		System.out.println("当前容器的长度: " + mq.getSize());
    		Thread t1 = new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				mq.put("f");
    				mq.put("g");
    			}
    		},"t1");	
    		
    		t1.start();
    		
    		Thread t2 = new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				Object o1 = mq.take();
    				System.out.println("移除的元素为: " + o1);
    				Object o2 = mq.take();
    				System.out.println("移除的元素为: " + o2);
    			}
    		},"t2");
    		
    		try {
    			TimeUnit.SECONDS.sleep(2);
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    		t2.start();
    	}
    
    }

package com.thread.message;
    
    public class ChangLock {
     
    	private String lock = "lock";
    	
    	private void method(){
    		synchronized (lock) {     //加锁跟没加锁没区别,因为锁改变了
    			try {
    				System.out.println("当前线程: " + Thread.currentThread().getName() + "开始");
    				lock = "change lock";
    				Thread.sleep(2000);
    				System.out.println("当前线程: " + Thread.currentThread().getName() + "结束");
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    	}
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
            final ChangLock changLock = new ChangLock();
            Thread t1 = new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				changLock.method();
    			}
    		},"t1");
            
            Thread t2 = new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				changLock.method();
    			}
    		},"t2");
            
            t1.start();
            
            try {
    			Thread.sleep(1000);
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
            t2.start();
    	}
    
    }

package com.thread.message;
    
    /**
     * 死锁问题,在设计程序时就应该避免双方持有对方锁的情况
     * @author Administrator
     *
     */
    public class DeadLock implements Runnable {
    
    	private String tag;
    	private static Object lock1 = new Object();
    	private static Object lock2 = new Object();
    	
    	public void setTag(String tag){
    		this.tag = tag;
    	}
    	@Override
    	public void run() {
    		// TODO Auto-generated method stub
           if(tag.equals("a")){
        	   synchronized (lock1) {
    			try {
    				System.out.println("当前线程: " + Thread.currentThread().getName() + "进入lock1执行");
    				Thread.sleep(2000);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    			synchronized (lock2){
    				System.out.println("当前线程: " + Thread.currentThread().getName() + "进入lock2执行");
    			}
    		}
           }
           
           if(tag.equals("b")){
        	   synchronized (lock2) {
    			try {
    				System.out.println("当前线程: " + Thread.currentThread().getName() + "进入lock2执行");
    				Thread.sleep(2000);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    			synchronized (lock1){
    				System.out.println("当前线程: " + Thread.currentThread().getName() + "进入lock1执行");
    			}
    		}
           }
           
           
    	}
    
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
            DeadLock d1 = new DeadLock();
            d1.setTag("a");
            DeadLock d2 = new DeadLock();
            d2.setTag("b");
            
            Thread t1 = new Thread(d1,"t1");
            Thread t2 = new Thread(d2,"t2");
            
            t1.start();
            try {
    			Thread.sleep(500);
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
            t2.start();
    	}
    
    }

package com.thread.message;
    
    public class ModifyLock {
    
    	private String name;
    	private int age;
    	
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public int getAge() {
    		return age;
    	}
    
    	public void setAge(int age) {
    		this.age = age;
    	}
    
    	public synchronized void changeAttributte(String name,int age){	
    		try {
    			System.out.println("当前线程: " + Thread.currentThread().getName() + "开始");
    			this.setName(name);
    			this.setAge(age);
    			
    			System.out.println("当前线程: " + Thread.currentThread().getName() + "修改对象内容为: " + this.name + "," + this.age);
    			Thread.sleep(2000);
    			System.out.println("当前线程: " + Thread.currentThread().getName() + "结束");
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    	}
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
           final ModifyLock modifyLock = new ModifyLock();
           Thread t1 = new Thread(new Runnable() {	
    		@Override
    		public void run() {
    			// TODO Auto-generated method stub
    			modifyLock.changeAttributte("张三", 20);
    		 }
    	   },"t1");
           
           Thread t2 = new Thread(new Runnable() {	
    		@Override
    		public void run() {
    			// TODO Auto-generated method stub
    			modifyLock.changeAttributte("李四", 21);
    		 }
    	  },"t2");
           
           t1.start();
           try {
    		Thread.sleep(1000);
    	 } catch (InterruptedException e) {
    		// TODO Auto-generated catch block
    		e.printStackTrace();
    	 }
           t2.start();
    	}
    
    }

package com.thread.message;
    
    public class ObjectLock {
    
    	public void method1(){
    	  synchronized (this) {     //对象锁
    		 try {
    			 System.out.println("do method1...");
    			Thread.sleep(2000);
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    	  }
    	}
    	
    	public void method2(){            //类锁
    		synchronized (ObjectLock.class) {
    			try {
    				System.out.println("do method2...");
    				Thread.sleep(2000);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    	}
    	
    	private Object lock = new Object();
    	public void method3(){              //任何对象锁
    		synchronized (lock) {
    			try {
    				System.out.println("do method3...");
    				Thread.sleep(2000);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    	}
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		final ObjectLock objLock = new ObjectLock();
    		Thread t1 = new Thread(new Runnable() {
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				objLock.method1();
    			}
    		},"t1");
    		
    		Thread t2 = new Thread(new Runnable() {	
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				objLock.method2();
    			}
    		},"t2");
    		
    		Thread t3 = new Thread(new Runnable() {
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				objLock.method3();
    			}
    		},"t3");
    	}
    
    }