Java并发知识总结

jixu

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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