# 使用notifyAll完善多線程下的生產者消費者模型 我們先看一下wait()的代碼注釋：  使當前線程等待，直到另一個線程調用了這個對象的notify()或notifyAll()方法，換句話說，這個方法是執行了wait(0); 當前線程必須擁有該對象的監視器。線程釋放此監視器的所有權，并等待另一個線程通過調用notify()或notifyAll()方法，讓這個對象監視器上等待的線程被喚醒，然后線程等待，直到它可以重新獲得監視器的所有權并恢復執行。 notify()是通知一個線程喚醒，而notifyAll()是會將wait()在同一個monitor的所有線程都會喚醒，而我們之前出現問題就是因為notify是隨機的，那么我們現在使用notifyAll試一下： ```java /** * @program: ThreadDemo * @description: 優化多線程下的生產者消費者模型，避免多生產者-多消費者造成的程序假死 * @author: hs96.cn@Gmail.com * @create: 2020-09-07 */ public class ProduceConsumerVersion3 { private int i = 0; private final Object LOCK = new Object(); private volatile boolean isProduced = false; public void produce() { synchronized (LOCK) { if (isProduced) { try { LOCK.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(Thread.currentThread().getName() + "->" + (++i)); LOCK.notifyAll(); isProduced = true; } } public void consume() { synchronized (LOCK) { if (!isProduced) { try { LOCK.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(Thread.currentThread().getName() + "->" + i); LOCK.notifyAll(); isProduced = false; } } public static void main(String[] args) { ProduceConsumerVersion3 pc = new ProduceConsumerVersion3(); Stream.of("P1", "P2", "P3").forEach(n -> new Thread(new Runnable() { @Override public void run() { while (true) { pc.produce(); try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } } } }, n).start()); Stream.of("C1", "C2", "C3", "C4").forEach(n -> new Thread(() -> { while (true) { pc.consume(); try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } } }, n).start()); } } ``` 運行效果如下：  可以看到有連續生產2個的情況，那么是什么原因導致的呢？ 其實仔細想一下，就是p3的生產完之后釋放鎖，然后p2搶到了，就繼續生產了，那么怎么解決呢？讓p2wait到p3生產的數據消費掉即可了，改進代碼如下：‘ ```java /** * @program: ThreadDemo * @description: 優化多線程下的生產者消費者模型，避免多生產者-多消費者造成的程序假死 * @author: hs96.cn@Gmail.com * @create: 2020-09-07 */ public class ProduceConsumerVersion3 { private int i = 0; private final Object LOCK = new Object(); private volatile boolean isProduced = false; public void produce() { synchronized (LOCK) { while (isProduced) { try { //System.out.println(Thread.currentThread().getName()+"wait...."); LOCK.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(Thread.currentThread().getName() + "->" + (++i)); LOCK.notifyAll(); isProduced = true; } } public void consume() { synchronized (LOCK) { while (!isProduced) { try { //System.out.println(Thread.currentThread().getName()+"wait...."); LOCK.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(Thread.currentThread().getName() + "->" + i); LOCK.notifyAll(); isProduced = false; } } public static void main(String[] args) { ProduceConsumerVersion3 pc = new ProduceConsumerVersion3(); Stream.of("P1", "P2", "P3").forEach(n -> new Thread(new Runnable() { @Override public void run() { while (true) { pc.produce(); try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } } } }, n).start()); Stream.of("C1", "C2", "C3", "C4").forEach(n -> new Thread(() -> { while (true) { pc.consume(); try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } } }, n).start()); } } ``` 運行效果如下：