Java并发知识总结

jixu

8. 并发

启动线程的几种方式

Thread t7 = new Thread(timer);

t7.start();

Thread.sleep(100) //暂停当前线程

class MT extends Thread {

  private int n;

  public MyThread( int n ){

    super();

    this.n=n;

  }

  public void run() {

    for(int i=0;i<n;i++) {

      System.out.println(i);

    }

  }

}

Class MT implements Runnable{

  private int n;

  public MyTask(int n){

    this.n = n;

  }

  public void run() {

    for(int i=0; i<n; i++) {

      System.out.println(i);

    }

  }

}

new Thread(){

  public void run() {

  for(int i=0; i<10; i++)

    System.out.println(i);

  }

}.start();

new Thread( ( ) -> {

  for(int i=0; i<10; i++)

    System.out.println(i);

} ).start();

线程同步

synchronize：对象加锁

synchronized(cnt) {

    cnt++;  //临界区

}

wait() 释放对象锁，阻塞当前进程
notify() / notifyAll() 相当于signal，让阻塞的线程继续

java并发API：java.util.concurrent
原子变量：保证线程安全
　　AtomicInteger cnt=new AtomicInteger(0);
　　cnt.getAndIncrement();
集合：
　　ArrayList/HashMap不是线程安全的
　　Vector及Hashtable是线程安全的
　　CopyOnWriteArrayList、 CopyOnWriteArraySet：适合于很少写入而读取频繁的对象
　　ConcurrentHashMap：putIfAbsent(), remove(), replace()
队列：
　　BlockingQueue<Integer> q=new ArrayBlockingQueue<>(3);　　　　put() take()

线程池

class ThreadPoolDemo

{

  public static void main(String[] args) {

    ExecutorService pool=Executors.newCachedThreadPool();

    MyTask t1=new MyTask(5);  MyTask t2=new MyTask(7);

    pool.execute(t1);         pool.execute(t2);

    pool.shutdown();

  }

}

class MyTask implements Runnable {

  int n=10;

  public MyTask(int n){ this.n=n;}

  public void run(){

    for(int i=0;i<n; i++)System.out.print(i);

  }

}

实现一个生产者-消费者问题

 class Producer extends Thread {

   private CubbyHole cubbyhole;

   private int number;

   public Producer(CubbyHole c, int number) {

     cubbyhole = c;

     this.number = number;

   }

   public void run() {

     for (int i = 0; i <10; i++)

       cubbyhole.put(i);

   }

 }

 class Consumer extends Thread {

   private CubbyHole cubbyhole;

   private int number;

   public Consumer(CubbyHole c, int number) {

     cubbyhole = c;

     this.number = number;

   }

   public void run() {

     int value = 0;

     for (int i = 0; i <10; i++)

       value = cubbyhole.get();

   }

 }

 class CubbyHole {

   private int data[] = new int[3];

   private int index = 0;

   public synchronized int get() {

     while (index <= 0) {

       try{

         wait(); //waits for notify() from Producer

       } catch (InterruptedException e) { }

     }

     index --;

     int value = data[index];

     System.out.println("Consumer got: " + data[index]);

     notify();

     return value;

   }

   public synchronized void put(int value) {

     while (index >= data.length) {

       try{

         wait(); //waits for notify() from consumer

       } catch (InterruptedException e) { }

     }

     System.out.println("Producer put: " + value);

     data[index] = value;

     index ++;

     notify();

   }

 }

 class ProducerConsumerStack {

   public static void main(String args[]) {

     CubbyHole c = new CubbyHole();

     Producer p1=new Producer(c,1);

     Consumer c1=new Consumer(c,1);

     p1.start();

     c1.start();

   }

 }

Ref：https://github.com/CyC2018/CS-Notes/blob/master/notes/Java%20%E5%B9%B6%E5%8F%91.md

巴特西

Java并发知识总结

8. 并发

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