线程基础知识点 notify()

最新推荐文章于 2024-03-18 18:12:02 发布

afeiod

最新推荐文章于 2024-03-18 18:12:02 发布

阅读量524

点赞数 1

分类专栏： j2se

本文链接：https://blog.youkuaiyun.com/afeiod/article/details/43185835

版权

j2se 专栏收录该内容

1 篇文章

订阅专栏

本文介绍了Java中wait()和notify()的基本使用原则，并通过实例详细展示了如何利用Condition实现队列缓冲区的多路通信，以及如何运用ReadWriteLock实现代理缓存。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

wait() , notify() 必须处在当前对象监视器(锁对象) 同步块内调用，否则会爆 current thread not owner; 即：IllegalMonitorStateException.

notify() 唤醒的线程也得与次对象监视器上的线程去竞争所有权（也包括当前调用notify() 自身线程在释放锁后也会去竞争）。

队列缓冲区：用Condition 线程通信机制多路通信实现。可参考： JDK帮助文档 Condition类

 class BoundedBuffer {
   final Lock lock = new ReentrantLock();
   final Condition notFull  = lock.newCondition(); 
   final Condition notEmpty = lock.newCondition(); 

   final Object[] items = new Object[100];
   int putptr, takeptr, count;

   public void put(Object x) throws InterruptedException {
     lock.lock();
     try {
       while (count == items.length) 
         notFull.await();
       items[putptr] = x; 
       if (++putptr == items.length) putptr = 0;
       ++count;
       notEmpty.signal();
     } finally {
       lock.unlock();
     }
   }

   public Object take() throws InterruptedException {
     lock.lock();
     try {
       while (count == 0) 
         notEmpty.await();
       Object x = items[takeptr]; 
       if (++takeptr == items.length) takeptr = 0;
       --count;
       notFull.signal();
       return x;
     } finally {
       lock.unlock();
     }
   } 
 }

代理缓存：  用 ReadWriteLock 读写锁机制实现， 参考JDK  ReentrantReadWriteLock类  class CachedData {
   Object data;
   volatile boolean cacheValid;
   ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();

   void processCachedData() {
     rwl.readLock().lock();
     if (!cacheValid) {
        // upgrade lock manually
        rwl.readLock().unlock();   // must unlock first to obtain writelock
        rwl.writeLock().lock();
        if (!cacheValid) { // recheck
          data = ...
          cacheValid = true;
        }
        // downgrade lock
        rwl.readLock().lock();  // reacquire read without giving up write lock
        rwl.writeLock().unlock(); // unlock write, still hold read
     }

     use(data);
     rwl.readLock().unlock();
   }
 }