2020大厂面试JUC线程重要技术点【集合+线程+阻塞队列+线程池】（上）

List<String> list = Collections.synchronizedList(new ArrayList<>());

List<String> list = new CopyOnWriteArrayList<>();

Collections.synchronizedMap();

是指尝试获取锁的线程不会阻塞，而是采用循环的方式来尝试乎获取锁，这样的好处就是减少线程上下文的切换消耗，缺点是循环会消耗CPU.
do
while()
CAS
期望值与工作区间的值比较

class MyCache{//缓存资源类
  //volatile 可见性 不保证原子性 禁止指令重排
  private volatile Map<String,Object> map = new HashMap<>();
  //解决问题 原子性
  //private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock ();
  public void put(String key,Object value){
    //加写锁
    rwLock.writeLock().lock();
    try{
      System.out.println(Thread.currentThread().getName()+"正在写入"+key);
      try{Time.MILLSECONDS.sleep(300);}catch(){};
      map.put(key,value);
      System.out.println(Thread.currentThread().getName()+"写入完成");
    }catch(Exception e){
    }finally{
      rwLock.writeLock().unlock();
    }
  }
  public void get(String key,Object value){
    //加读锁
    rwLock.readLock().lock();
    try{
    System.out.println(Thread.currentThread().getName()+"正在读取"+key);
    try{Time.MILLSECONDS.sleep(300);}catch(){};
    Object result = map.get(key);
    System.out.println(Thread.currentThread().getName()+"读取完成"+result);
    }catch(Exception e){
    }finally{
      rwLock.readLock().unlock();
    }
  }
}
public class ReadWriteLockDemo{
  public static void main(String[] args){
    MyCache myCache = new MyCache();
    //写
    for(int i = 1;i <= 5;i++){
      new Thread(() -> {
        final int tempInt = i;
        myCache.put(tempInt+"",tempInt+"");
      },String.valueOf(i)).start();
    }
    //读
    for(int i = 1;i <= 5;i++){
      new Thread(() -> {
        final int tempInt = i;
        myCache.get(tempInt+"");
      },String.valueOf(i)).start();
    }
  }
}

public class CountDownLatchDemo{
  public static void main(String[] args){
    for(int i = 1;i<=6;i++){
      new Thread(()->{
        System.out.println(Thread.currentThread().getName()+"上完自习，离开教室");
      },String.valueOf(i)).start(); 
    }
    System.out,println(Thread.currentThread().getName()+"班长最后关门走人");
  }
}

public class CountDownLatchDemo{
  public static void main(String[] args){
    // 计数
    CountDownLatch countDownLatch = new CountDownLatch(6);
    for(int i = 1;i<=6;i++){
      new Thread(()->{
        System.out.println(Thread.currentThread().getName()+"上完自习，离开教室");
        countDownLatch.countDown();//减1操作
      },String.valueOf(i)).start(); 
    }
    // 主线程等待
    countDownLatch.await();
    System.out,println(Thread.currentThread().getName()+"班长锁门，最后关门走人");
  }
}

public class CountDownLatchDemo{
  public static void main(String[] args){
    CyclicBarrier cyclicBarrier = new CyclicBarrier(7,()->{System.out.println("***召唤神龙***");});
    for(int i = 1;i<=7;i++){
      final int tempInt  = i;
      new Thread(()->{
        System.out.println(Thread.currentThread().getName()+"收集到第"+tempInt +"颗龙珠");
        cyclicBarrier.await();
      },String.valueOf(i)).start();
    }
  }
}

public class CountDownLatchDemo{
  public static void main(String[] args){
    // 模拟3个停车位
    Semaphore semaphore = new Semaphore(3);
    for(int i = 1; i <= 6;i++){
      new Thread(()->{
        try{
          semaphore.acquire();
          System.out.println(Thread.currentThread().getName()+"抢到车位");
          TimeUnit.SECONDS.sleep(3);
          System.out.println(Thread.currentThread().getName()+"停车3S后，离开车位");
        }catch(...){
        }finally{
          semaphore.release();
        } 
      },String.valueOf(i)).start();
    }
  }
}