Java线程间通信的几种方式

文章目录

一、使用同一个共享变量控制

二、PipedInputStream、PipedOutputStream

三、利用BlockingQueue

四、利用LockSupport

五、利用ThreadLocal

 

一、使用同一个共享变量控制

Synchronized、wait、notify

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public class Demo1 {
 
    private final List<Integer> list =new ArrayList<>();
 
    public static void main(String[] args) {
        Demo1 demo =new Demo1();
        new Thread(()->{
            for (int i=0;i<10;i++){
                synchronized (demo.list){
                    if(demo.list.size()%2==1){
                        try {
                            demo.list.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    demo.list.add(i);
                    System.out.print(Thread.currentThread().getName());
                    System.out.println(demo.list);
                    demo.list.notify();
                }
            }
 
        }).start();
 
        new Thread(()->{
            for (int i=0;i<10;i++){
                synchronized (demo.list){
                    if(demo.list.size()%2==0){
                        try {
                            demo.list.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    demo.list.add(i);
                    System.out.print(Thread.currentThread().getName());
                    System.out.println(demo.list);
                    demo.list.notify();
                }
            }
        }).start();
    }
}

Lock、Condition

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public class Task {
    private final Lock lock = new ReentrantLock();
 
    private final Condition addConditon = lock.newCondition();
    private final Condition subConditon = lock.newCondition();
 
    private volatile int num = 0;
    private List<String> list = new ArrayList<>();
 
    public void add() {
        for (int i = 0; i < 10; i++) {
            lock.lock();
 
            try {
                if (list.size() == 10) {
                    addConditon.await();
                }
                num++;
                Thread.sleep(100);
                list.add("add " + num);
                System.out.println("The list size is " + list.size());
                System.out.println("The add thread is " + Thread.currentThread().getName());
                System.out.println("-------------");
                subConditon.signal();
 
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }
 
    public void sub() {
        for (int i = 0; i < 10; i++) {
            lock.lock();
 
            try {
 
                if (list.size() == 0) {
                    subConditon.await();
                }
                num--;
                Thread.sleep(100);
                list.remove(0);
                System.out.println("The list size is " + list.size());
                System.out.println("The sub thread is " + Thread.currentThread().getName());
                System.out.println("-------------");
                addConditon.signal();
 
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }
 
 
    public static void main(String[] args) {
        Task task = new Task();
        new Thread(task::add).start();
        new Thread(task::sub).start();
    }
}

利用volatile

volatile修饰的变量值直接存在主内存里面，子线程对该变量的读写直接写住内存，而不是像其它变量一样在local thread里面产生一份copy。volatile能保证所修饰的变量对于多个线程可见性，即只要被修改，其它线程读到的一定是最新的值。

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public class Demo2 {
    private volatile List<Integer> list =new ArrayList<>();
    public static void main(String[] args) {
        Demo2 demo =new Demo2();
        new Thread(()->{
            for (int i=0;i<10;i++){
                    demo.list.add(i);
                    System.out.print(Thread.currentThread().getName());
                    System.out.println(demo.list);
            }
 
        }).start();
 
        new Thread(()->{
            for (int i=0;i<10;i++){
                    demo.list.add(i);
                    System.out.print(Thread.currentThread().getName());
                    System.out.println(demo.list);
                }
        }).start();
    }
}

利用AtomicInteger

和volatile类似, 只是原子操作达到预估值非A即B

二、PipedInputStream、PipedOutputStream

这里用流在两个线程间通信，但是Java中的Stream是单向的，所以在两个线程中分别建了一个input和output

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public class PipedDemo {
 
    private final PipedInputStream inputStream1;
    private final PipedOutputStream outputStream1;
    private final PipedInputStream inputStream2;
    private final PipedOutputStream outputStream2;
 
    public PipedDemo(){
        inputStream1 = new PipedInputStream();
        outputStream1 = new PipedOutputStream();
        inputStream2 = new PipedInputStream();
        outputStream2 = new PipedOutputStream();
        try {
            inputStream1.connect(outputStream2);
            inputStream2.connect(outputStream1);
        } catch (IOException e) {
            e.printStackTrace();
        }
 
    }
    /**程序退出时，需要关闭stream*/
    public void shutdown() throws IOException {
        inputStream1.close();
        inputStream2.close();
        outputStream1.close();
        outputStream2.close();
    }
 
 
    public static void main(String[] args) throws IOException {
        PipedDemo demo =new PipedDemo();
        new Thread(()->{
            PipedInputStream in = demo.inputStream2;
            PipedOutputStream out = demo.outputStream2;
 
            for (int i = 0; i < 10; i++) {
                try {
                    byte[] inArr = new byte[2];
                    in.read(inArr);
                    System.out.print(Thread.currentThread().getName()+": "+i+" ");
                    System.out.println(new String(inArr));
                    while(true){
                        if("go".equals(new String(inArr)))
                            break;
                    }
                    out.write("ok".getBytes());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
 
        }).start();
 
        new Thread(()->{
            PipedInputStream in = demo.inputStream1;
            PipedOutputStream out = demo.outputStream1;
 
            for (int i = 0; i < 10; i++) {
                try {
                    out.write("go".getBytes());
                    byte[] inArr = new byte[2];
                    in.read(inArr);
                    System.out.print(Thread.currentThread().getName()+": "+i+" ");
                    System.out.println(new String(inArr));
                    while(true){
                        if("ok".equals(new String(inArr)))
                            break;
                    }
 
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
 
        }).start();
//        demo.shutdown();
    }
}

输出:

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Thread-0: 0 go
Thread-1: 0 ok
Thread-0: 1 go
Thread-1: 1 ok
Thread-0: 2 go
Thread-1: 2 ok
Thread-0: 3 go
Thread-1: 3 ok
Thread-0: 4 go
Thread-1: 4 ok
Thread-0: 5 go
Thread-1: 5 ok
Thread-0: 6 go
Thread-1: 6 ok
Thread-0: 7 go
Thread-1: 7 ok
Thread-0: 8 go
Thread-1: 8 ok
Thread-0: 9 go
Thread-1: 9 ok

三、利用BlockingQueue

BlockingQueue定义的常用方法如下:

  • add(Object)：把Object加到BlockingQueue里，如果BlockingQueue可以容纳，则返回true，否则抛出异常。
  • offer(Object)：表示如果可能的话，将Object加到BlockingQueue里，即如果BlockingQueue可以容纳，则返回true，否则返回false。
  • put(Object)：把Object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里有空间再继续。
  • poll(time)：获取并删除BlockingQueue里排在首位的对象，若不能立即取出，则可以等time参数规定的时间，取不到时返回null。当不传入time值时，立刻返回。
  • peek()：立刻获取BlockingQueue里排在首位的对象，但不从队列里删除，如果队列为空，则返回null。
  • take()：获取并删除BlockingQueue里排在首位的对象，若BlockingQueue为空，阻断进入等待状态直到BlockingQueue有新的对象被加入为止。

BlockingQueue有四个具体的实现类：

  • ArrayBlockingQueue：数组阻塞队列，规定大小，其构造函数必须带一个int参数来指明其大小。其所含的对象是以FIFO（先入先出）顺序排序的。
  • LinkedBlockingQueue：链阻塞队列，大小不定，若其构造函数带一个规定大小的参数，生成的BlockingQueue有大小限制，若不带大小参数，所生成的BlockingQueue的大小由Integer.MAX_VALUE来决定。其所含的对象是以FIFO顺序排序的。
  • PriorityBlockingQueue：类似于LinkedBlockingQueue,但其所含对象的排序不是FIFO，而是依据对象的自然排序顺序或者是构造函数所带的Comparator决定的顺序。
  • SynchronousQueue：特殊的BlockingQueue，它的内部同时只能够容纳单个元素，对其的操作必须是放和取交替完成的。
  • DelayQueue：延迟队列，注入其中的元素必须实现 java.util.concurrent.Delayed 接口

所有BlockingQueue的使用方式类似，以下例子一个线程写入，一个线程读取，操作的是同一个Queue：

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public class BlockingQueueDemo {
 
    public static void main(String[] args) {
        LinkedBlockingQueue<String> queue = new LinkedBlockingQueue<>();
        //读线程
        new Thread(() -> {
            int i =0;
            while (true) {
                try {
                    String item = queue.take();
                    System.out.print(Thread.currentThread().getName() + ": " + i + " ");
                    System.out.println(item);
                    i++;
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
        //写线程
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    String item = "go"+i;
                    System.out.print(Thread.currentThread().getName() + ": " + i + " ");
                    System.out.println(item);
                    queue.put(item);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}

四、利用LockSupport

用LockSupport的unpark()和park()方法，实现线程间通信。

 

五、利用ThreadLocal

ThreadLocal，即线程变量，是一个以 ThreadLocal 对象为键、任意对象为值的存储结构。这个结构被依附在线程上，也就是说一个线程可以根据一个 ThreadLocal 对象查询到绑定在这个线程上的一个值。

可以通过 set(T) 方法来设置一个值，在当前线程下再通过 get() 方法获取到原先设置的值。

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public class ThreadLocalDemo {
 
    private static final ThreadLocal<Long> TIME_THREADLOCAL = new ThreadLocal<>() {
        @Override
        protected Long initialValue() {
            return System.currentTimeMillis();
        }
    };
 
    public static final void begin() {
        TIME_THREADLOCAL.set(System.currentTimeMillis());
    }
 
    public static final long end() {
        return System.currentTimeMillis() - TIME_THREADLOCAL.get();
    }
 
    public static void main(String[] args) throws InterruptedException {
        ThreadLocalDemo.begin();
        Thread.sleep(2000);
        System.out.println(ThreadLocalDemo.end());
    }
}
//输出 2003

 

posted @   47号Gamer丶  阅读(1189)  评论(0)  编辑  收藏  举报
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