Effective Java - 并发工具优先于 wait 和

第81条 并发工具优先于 wait 和 notify

1. 比较常见的同步器：CountDownLatch、Semaphore、CyclicBarrier、Exchanger、Phaser

2. CountDownLatch的用法:

   public static long time(Executor executor, int concurrency, Runnable action) throws InterruptedException {
       CountDownLatch ready = new CountDownLatch(concurrency);
       CountDownLatch start = new CountDownLatch(1);
       CountDownLatch done = new CountDownLatch(concurrency);
       for (int i = 0; i < concurrency; i++) {
           executor.execute(() -> {
               ready.countDown(); // Tell timer we're ready
               try {
                   start.await(); // Wait till peers are ready
                   action.run();
               } catch (InterruptedException e) {
                   Thread.currentThread().interrupt();
               } finally {
                   done.countDown(); // Tell timer we're done
               }
           });
       }
       ready.await(); // Wait for all workers to be ready
       long startNanos = System.nanoTime();
       start.countDown(); // And they're off!
       done.await(); // Wait for all workers to finish
       return System.nanoTime() - startNanos;
   }
   

3. 始终应该使用 while 循环模式来调用 wait 方法；永远不要在循环之外调用 wait 方法

4. 不应该在新代码中使用wait和notify

思考

1. 应该有空了解下Java的concurrent库提供的内容，由Doug Lea开发的AQS
2. wait和notify本身并不会太重要，但是基本的原理还是要了解下。本科期间找实习，一个笔试题就是让用这两个函数，实现两个线程，按顺序输出26个英文字母