如何在Java中正确实现生产者消费者模式。

huangapple
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英文:

how to properly implement producer - consumer in Java

问题

我是您的中文翻译，以下是翻译好的内容：

我是这样实现生产者消费者的。

但是它抛出了错误。

我尝试使用了使用锁的这种方法。链接

  1. class Testclass {
  2.     Boolean isFresh = false;
  3.     int count = 0;
  4.     public synchronized void GET(String threadName){
  5.         while(!isFresh){
  6.             try {
  7.                 isFresh.wait();
  8.             } catch (InterruptedException e) {
  9.                 e.printStackTrace();
  10.             }
  11.         }
  12.         System.out.println("GET方法被调用：" + count + " " + threadName);
  13.         isFresh = false;
  14.         isFresh.notify();
  16.     }
  18.     public synchronized void PUT(String threadName){
  19.         while(isFresh){
  20.             try{
  21.                 isFresh.wait();
  22.             }catch( InterruptedException e){
  23.                 e.printStackTrace();
  24.             }
  25.         }
  26.         count++;
  27.         System.out.println("PUT方法被调用：" + count + " " + threadName);
  28.         isFresh = true;
  29.         isFresh.notify();
  30.     }
  32. }
  33. class Producer implements Runnable{
  34.     Testclass q;
  35.     String name;
  36.     Producer(Testclass q, String name){
  37.         this.q = q;
  38.         this.name = name;
  39.     }
  40.     public void run(){
  41.         while(true){
  42.             int time = (int)(Math.random() * 10000);
  44.             try {
  45.                 Thread.sleep(time);
  46.             } catch (InterruptedException e) {
  47.                 e.printStackTrace();
  48.             }
  49.             q.PUT(this.name);
  50.         }
  52.     }
  53. }
  55. class Consumer implements Runnable{
  56.     Testclass q;
  57.     String name ;
  58.     Consumer(Testclass q,String name){
  59.         this.q = q;
  60.         this.name = name;
  61.     }
  62.     public void run(){
  63.         while(true){
  64.             int time = (int)(Math.random() * 10000);
  66.             try {
  67.                 Thread.sleep(time);
  68.             } catch (InterruptedException e) {
  69.                 e.printStackTrace();
  70.             }
  71.             q.GET(this.name);
  72.         }
  74.     }
  75. }
  77. public class Main {
  78.     public static void main(String[] args){
  79.         Testclass t = new Testclass();
  80.         Thread t1 = new Thread(new Consumer(t, "消费者 1"));
  81.         Thread t2 = new Thread(new Consumer(t, "消费者 2"));
  82.         Thread t3 = new Thread(new Producer(t, "生产者 1"));
  83.         Thread t4 = new Thread(new Producer(t, "生产者 2"));
  84.         t1.start();
  85.         t2.start();
  86.         t3.start();
  87.         t4.start();
  88.         try{
  89.             t1.join();
  90.         }catch (InterruptedException e){
  91.             e.printStackTrace();
  92.         }
  94.     }
  95. }

这个实现会抛出以下错误。

请解释为什么所有线程都抛出了 Illegal MonitorStateException 错误？

  1. PUT方法被调用：1 生产者 1
  2. Exception in thread "Thread-2" java.lang.IllegalMonitorStateException: 当前线程不是所有者
  3. 	at java.base/java.lang.Object.notify(Native Method)
  4. 	at Testclass.PUT(Main.java:34)
  5. 	at Producer.run(Main.java:54)
  6. 	at java.base/java.lang.Thread.run(Thread.java:832)
  7. GET方法被调用：1 消费者 1
  8. Exception in thread "Thread-0" java.lang.IllegalMonitorStateException: 当前线程不是所有者
  9. 	at java.base/java.lang.Object.notify(Native Method)
  10. 	at Testclass.GET(Main.java:19)
  11. 	at Consumer.run(Main.java:76)
  12. 	at java.base/java.lang.Thread.run(Thread.java:832)
  13. Exception in thread "Thread-1" java.lang.IllegalMonitorStateException: 当前线程不是所有者
  14. 	at java.base/java.lang.Object.wait(Native Method)
  15. 	at java.base/java.lang.Object.wait(Object.java:321)
  16. 	at Testclass.GET(Main.java:12)
  17. 	at Consumer.run(Main.java:76)
  18. 	at java.base/java.lang.Thread.run(Thread.java:832)
  19. PUT方法被调用：2 生产者 2
  20. Exception in thread "Thread-3" java.lang.IllegalMonitorStateException: 当前线程不是所有者
  21. 	at java.base/java.lang.Object.notify(Native Method)
  22. 	at Testclass.PUT(Main.java:34)
  23. 	at Producer.run(Main.java:54)
  24. 	at java.base/java.lang.Thread.run(Thread.java:832)
  26. Process finished with exit code 0

我想知道为什么输出会是这样的？正确的实现方法是什么？

英文:

I implemented producer consumer like this.

But it is throwing error.

I tried to use this method of using lock. Link

  1. class Testclass {
  2.     Boolean isFresh = false;
  3.     int count = 0;
  4.     public synchronized void GET(String threadName){
  5.         while(!isFresh){
  6.             try {
  7.                 isFresh.wait();
  8.             } catch (InterruptedException e) {
  9.                 e.printStackTrace();
  10.             }
  11.         }
  12.         System.out.println("GET method was called : " + count + " " + threadName);
  13.         isFresh = false;
  14.         isFresh.notify();
  16.     }
  18.     public synchronized void PUT(String threadName){
  19.         while(isFresh){
  20.             try{
  21.                 isFresh.wait();
  22.             }catch( InterruptedException e){
  23.                 e.printStackTrace();
  24.             }
  25.         }
  26.         count++;
  27.         System.out.println("PUT method was called : " + count + " " + threadName);
  28.         isFresh = true;
  29.         isFresh.notify();
  30.     }
  32. }
  33. class Producer implements Runnable{
  34.     Testclass q;
  35.     String name;
  36.     Producer(Testclass q, String name){
  37.         this.q = q;
  38.         this.name = name;
  39.     }
  40.     public void run(){
  41.         while(true){
  42.             int time = (int)(Math.random() * 10000);
  44.             try {
  45.                 Thread.sleep(time);
  46.             } catch (InterruptedException e) {
  47.                 e.printStackTrace();
  48.             }
  49.             q.PUT(this.name);
  50.         }
  52.     }
  53. }
  55. class Consumer implements Runnable{
  56.     Testclass q;
  57.     String name ;
  58.     Consumer(Testclass q,String name){
  59.         this.q = q;
  60.         this.name = name;
  61.     }
  62.     public void run(){
  63.         while(true){
  64.             int time = (int)(Math.random() * 10000);
  66.             try {
  67.                 Thread.sleep(time);
  68.             } catch (InterruptedException e) {
  69.                 e.printStackTrace();
  70.             }
  71.             q.GET(this.name);
  72.         }
  74.     }
  75. }
  78. public class Main {
  79.     public static void main(String[] args){
  80.         Testclass t = new Testclass();
  81.         Thread t1 = new Thread(new Consumer(t, "consumer 1"));
  82.         Thread t2 = new Thread(new Consumer(t, "consumer 2"));
  83.         Thread t3 = new Thread(new Producer(t, "producer 1"));
  84.         Thread t4 = new Thread(new Producer(t, "producer 2"));
  85.         t1.start();
  86.         t2.start();
  87.         t3.start();
  88.         t4.start();
  89.         try{
  90.             t1.join();
  91.         }catch (InterruptedException e){
  92.             e.printStackTrace();
  93.         }
  95.     }
  99. }

this implementation throws following error.

Please explain
why all the threads are throwing Illegal MonitorStateException?

  1. PUT method was called : 1 producer 1
  2. Exception in thread "Thread-2" java.lang.IllegalMonitorStateException: current thread is not owner
  3. 	at java.base/java.lang.Object.notify(Native Method)
  4. 	at Testclass.PUT(Main.java:34)
  5. 	at Producer.run(Main.java:54)
  6. 	at java.base/java.lang.Thread.run(Thread.java:832)
  7. GET method was called : 1 consumer 1
  8. Exception in thread "Thread-0" java.lang.IllegalMonitorStateException: current thread is not owner
  9. 	at java.base/java.lang.Object.notify(Native Method)
  10. 	at Testclass.GET(Main.java:19)
  11. 	at Consumer.run(Main.java:76)
  12. 	at java.base/java.lang.Thread.run(Thread.java:832)
  13. Exception in thread "Thread-1" java.lang.IllegalMonitorStateException: current thread is not owner
  14. 	at java.base/java.lang.Object.wait(Native Method)
  15. 	at java.base/java.lang.Object.wait(Object.java:321)
  16. 	at Testclass.GET(Main.java:12)
  17. 	at Consumer.run(Main.java:76)
  18. 	at java.base/java.lang.Thread.run(Thread.java:832)
  19. PUT method was called : 2 producer 2
  20. Exception in thread "Thread-3" java.lang.IllegalMonitorStateException: current thread is not owner
  21. 	at java.base/java.lang.Object.notify(Native Method)
  22. 	at Testclass.PUT(Main.java:34)
  23. 	at Producer.run(Main.java:54)
  24. 	at java.base/java.lang.Thread.run(Thread.java:832)
  26. Process finished with exit code 0

I want to know why is the output like that?
and what is the correct way of implementing it?

答案1

得分: 0

你应该使用 BlockingQueue。这样你就不需要使用 wait/notify，甚至不需要使用 synchronized。

  1. class Testclass {
  2.     BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(1);
  3.     AtomicInteger count = new AtomicInteger(0);
  4.     public void GET(String threadName) throws InterruptedException{
  5.         Integer i = queue.take();
  6.         count.getAndIncrement();
  7.         System.out.println("GET method was called : " + count + " " + threadName);
  8.     }
  10.     public void PUT(String threadName) throws InterruptedException{
  12.         int c = count.get();
  13.         queue.put(c);
  14.         count.getAndIncrement();
  15.         System.out.println("PUT method was called : " + count + " " + threadName);
  16.     }
  18. }

我不确定你想如何处理 count 变量。通过更改队列大小，可以轻松地进行扩展。

英文:

You should use a BlockingQueue. Then you don't have to use wait/notify or even synchronzied.

  1. class Testclass {
  2.     BlockingQueue&lt;Integer&gt; queue = new ArrayBlockingQueue(1);
  3.     AtomicInteger count = new AtomicInteger(0);
  4.     public void GET(String threadName) throws InterruptedException{
  5.         Integer i = queue.take();
  6.         count.getAndIncrement();
  7.         System.out.println(&quot;GET method was called : &quot; + count + &quot; &quot; + threadName);
  8.     }
  10.     public void PUT(String threadName) throws InterruptedException{
  12.         int c = count.get();
  13.         queue.put(c);
  14.         count.getAndIncrement();
  15.         System.out.println(&quot;PUT method was called : &quot; + count + &quot; &quot; + threadName);
  16.     }
  18. }

I'm not sure what you want to do with count. This is readily extensible by changing the size of your Queue.

huangapple
  • 本文由 发表于 2020年7月27日 17:17:31
  • 转载请务必保留本文链接：https://java.coder-hub.com/63112235.html
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