第81條 并發(fā)工具優(yōu)先于 wait 和 notify

1. 比較常見的同步器：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. 始終應(yīng)該使用 while 循環(huán)模式來調(diào)用 wait 方法；永遠(yuǎn)不要在循環(huán)之外調(diào)用 wait 方法

4. 不應(yīng)該在新代碼中使用wait和notify

思考

1. 應(yīng)該有空了解下Java的concurrent庫提供的內(nèi)容，由Doug Lea開發(fā)的AQS
2. wait和notify本身并不會太重要，但是基本的原理還是要了解下。本科期間找實(shí)習(xí)，一個筆試題就是讓用這兩個函數(shù)，實(shí)現(xiàn)兩個線程，按順序輸出26個英文字母