java多线程笔记--顺序执行

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java多线程笔记–多线程顺序执行

文章目录


参考: https://www.cnblogs.com/xiaoxi/p/8035725.html

https://blog.csdn.net/hefenglian/article/details/82596072

https://blog.csdn.net/Evankaka/article/details/80800081

1.java多线程笔记–顺序执行

1.使用join
如在线程B中调用了线程A的Join()方法,直到线程A执行完毕后,才会继续执行线程B
2.使用CountDownLatch
await方法阻塞当前线程,当CountDownLatch减为0时就代表条件已成熟,所有因调用await方法而阻塞的线程都会被唤醒
3.使用阻塞队列,利用队列的FIFO特性
4.使用newSingleThreadExecutor内部,线程池的newSingleThreadExecutor内部使用一个容量不限的阻塞队列,同3类似

2.java多线程笔记–循环顺序打印问题

解决:3个线程1、2、3依次执行打印ABC,但是实际处理的时候不一定先执行线程1打印A,具体跟判断逻辑有关,比如先执行了线程3,但是run中判断满足条件才输出。

2.1通过Lock、3个Condition的等待唤醒机制和状态变量判断,来控制3个线程输出顺序

public class PrintABCByLockAndCondition 
    private static Lock lock = new ReentrantLock();
    private static Condition conditionA = lock.newCondition();
    private static Condition conditionB = lock.newCondition();
    private static Condition conditionC = lock.newCondition();
    private static int status = 0;

    public static void main(String[] args) 
        new PrintABCByLockAndCondition().printABC();
    

    public void printABC() 
        ExecutorService service = Executors.newFixedThreadPool(3);
        //线程的执行顺序跟提交顺序无关
        service.execute(new RunnableC());
        service.execute(new RunnableB());
        service.execute(new RunnableA());
        service.shutdown();
    

    private class RunnableA implements Runnable 
        @Override
        public void run() 
            try 
                lock.lock();
                while (true) 
                    while (status % 3 != 0) //注意这里是不等于0,也就是说没轮到该线程执行,之前一直等待状态
                        conditionA.await();//释放了锁,进入阻塞等待,依赖C唤醒
                    
                    System.out.print("A");
                    status++;
                    conditionB.signal(); // A执行完唤醒B线程
                

             catch (InterruptedException e) 
                e.printStackTrace();
             finally 
                lock.unlock();
            

        
    

    private class RunnableB implements Runnable 
        @Override
        public void run() 

            try 
                lock.lock();
                while (true) 
                    while (status % 3 != 1) 
                        conditionB.await();
                    
                    System.out.print("B");
                    status++;
                    conditionC.signal(); // B执行完唤醒C线程
                
             catch (InterruptedException e) 
                e.printStackTrace();
             finally 
                lock.unlock();
            

        
    

    private class RunnableC implements Runnable 
        @Override
        public void run() 
            try 
                lock.lock();
                while (true) 
                    while (status % 3 != 2) 
                        conditionC.await();
                    
                    System.out.println("C");
                    status++;
                    conditionA.signal(); // C执行完唤醒A线程
                

             catch (InterruptedException e) 
                e.printStackTrace();
             finally 
                lock.unlock();
            
        
    

2.2通过Lock和状态变量判断,来控制3个线程输出顺序

public class PrintABCByLock 
    private static Lock lock = new ReentrantLock();
    private static int status = 0;

    public static void main(String[] args) 
        new PrintABCByLock().printABC();
    

    public void printABC() 
        ExecutorService service = Executors.newFixedThreadPool(3);
        //线程的执行顺序跟提交顺序无关
        service.execute(new RunnableC());
        service.execute(new RunnableB());
        service.execute(new RunnableA());
        service.shutdown();
    

    private class RunnableA implements Runnable 
        @Override
        public void run() 
            while (true) 
                try 
                    lock.lock();
                    while (status % 3 == 0) 
                        System.out.print("A");
                        status++;
                    
                 finally 
                    lock.unlock();
                
            
        
    

    private class RunnableB implements Runnable 
        @Override
        public void run() 
            while (true) 
                try 
                    lock.lock();
                    while (status % 3 == 1) 
                        System.out.print("B");
                        status++;
                    
                 finally 
                    lock.unlock();
                
            
        
    

    private class RunnableC implements Runnable 
        @Override
        public void run() 
            while (true) 
                try 
                    lock.lock();
                    while (status % 3 == 2) 
                        System.out.println("C");
                        status++;
                    
                 finally 
                    lock.unlock();
                
            

        
    

2.3通过3个信号量,每个信号量的最大许可为1,来控制3个输出顺序

public class PrintABCBySemaphore 

    //信号量,表示可用的许可数量,用于控制同时容许访问的线程数量
    public Semaphore s1 = new Semaphore(1);
    public Semaphore s2 = new Semaphore(0);
    public Semaphore s3 = new Semaphore(0);

    public static void main(String[] args) 
        new PrintABCBySemaphore().printABC();
    

    public void printABC() 
        ExecutorService exe = Executors.newFixedThreadPool(3);
        exe.execute(new RunnableC());
        exe.execute(new RunnableA());
        exe.execute(new RunnableB());
        exe.shutdown();
    

    private class RunnableA implements Runnable 
        @Override
        public void run() 
            while (true) 
                try 
                    s1.acquire();//获取信号量,s1 - 1
                    System.out.print("A");
                    s2.release();//释放信号量,s2 + 1
                 catch (InterruptedException e) 
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                
            
        
    

    private class RunnableB implements Runnable 
        @Override
        public void run() 
            while (true) 
                try 
                    s2.acquire();//获取信号量,s2 - 1
                    System.out.print("B");
                    s3.release();//释放信号量,s3 + 1
                 catch (InterruptedException e) 
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                
            
        
    

    private class RunnableC implements Runnable 
        @Override
        public void run() 
            while (true) 
                try 
                    s3.acquire();//获取信号量,s3 - 1
                    System.out.println("C");
                    s1.release();//释放信号量,s1 + 1
                 catch (InterruptedException e) 
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                
            
        
    

2.4通过Atomic原子自增和3个线程的判断逻辑,来控制3个线程输出顺序

public class PrintABCByAtomic 
    private AtomicInteger status = new AtomicInteger(0);

    public static void main(String[] args) 
        new PrintABCByAtomic().printABC();
    

    public void printABC() 

        ExecutorService service = Executors.newFixedThreadPool(3);
        //线程的执行顺序跟提交顺序无关
        service.execute(new RunnableC());
        service.execute(new RunnableB());
        service.execute(new RunnableA());
        service.shutdown();
    

    private class RunnableA implements Runnable 
        @Override
        public void run() 
            while (true) 
                if (status.get() % 3 == 0) 
                    System.out.print("A");
                    status.getAndIncrement();
                
            
        
    

    private class RunnableB implements Runnable 
        @Override
        public void run() 
            while (true) 
                if (status.get() % 3 == 1) 
                    System.out.print("B");
                    status.getAndIncrement();
                
            
        
    

    private class RunnableC implements Runnable 
        @Override
        public void run() 
            while (true) 
                if (status.get() % 3 == 2) 
                    System.out.println("C");
                    status.getAndIncrement();
                
            

        
    

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