Thread--生产者消费者假死分析

Posted 2020-08-30 MicroCat

1 package p_c_allWait;
2 
3 public class ValueObject {
4     
5     public static String value = "";
6 
7 }

 1 package p_c_allWait;
 2 
 3 public class P {
 4     
 5     private String lock;
 6 
 7     public P(String lock) {
 8         super();
 9         this.lock = lock;
10     }
11     
12     public void setValue() {
13         try {
14             synchronized (lock) {
15                 while(!ValueObject.value.equals("")) {
16                     System.out.println("生产者 " + Thread.currentThread().getName() + " WAITING 了");
17                     lock.wait();
18                 }
19                 System.out.println("生产者 " + Thread.currentThread().getName() + " RUNNABLE 了");
20                 String value = System.currentTimeMillis() + "_" + System.nanoTime();
21                 ValueObject.value = value;
22                 lock.notify();
23             }
24         } catch (Exception e) {
25             // TODO: handle exception
26             e.printStackTrace();
27         }
28     }
29 
30 }

 1 package p_c_allWait;
 2 
 3 public class C {
 4     
 5     private String lock;
 6 
 7     public C(String lock) {
 8         super();
 9         this.lock = lock;
10     }
11     
12     public void getValue() {
13         try {
14             synchronized (lock) {
15                 while(ValueObject.value.equals("")) {
16                     System.out.println("消费者 " + Thread.currentThread().getName() + " wating 了");
17                     lock.wait();
18                 }
19                 System.out.println("消费者 " + Thread.currentThread().getName() + " RUNNABLE 了");
20                 ValueObject.value = "";
21                 lock.notify();
22             }
23         } catch (Exception e) {
24             // TODO: handle exception
25             e.printStackTrace();
26         }
27     }
28 
29 }

 1 package p_c_allWait;
 2 
 3 public class ThreadP extends Thread {
 4 
 5     private P p;
 6 
 7     public ThreadP(P p) {
 8         super();
 9         this.p = p;
10     }
11 
12     @Override
13     public void run() {
14         while(true) {
15             p.setValue();
16         }
17     }
18 
19 }

 1 package p_c_allWait;
 2 
 3 public class ThreadC extends Thread {
 4 
 5     private C c;
 6 
 7     public ThreadC(C c) {
 8         super();
 9         this.c = c;
10     }
11 
12     @Override
13     public void run() {
14         while(true) {
15             c.getValue();
16         }
17     }
18     
19     
20     
21 }

 1 package p_c_allWait;
 2 
 3 public class Run {
 4     
 5     public static void main(String[] args) {
 6         String lock = "";
 7         P p = new P(lock);
 8         C r = new C(lock);
 9         ThreadP[] pThread = new ThreadP[2];
10         ThreadC[] cThread = new ThreadC[2];
11         for(int i=0; i<2; i++) {
12             pThread[i] = new ThreadP(p);
13             pThread[i].setName("生产者 " + (i+1));
14             cThread[i] = new ThreadC(r);
15             cThread[i].setName("消费者 " + (i+1));
16             pThread[i].start();
17             cThread[i].start();
18         }
19     }
20 
21 }

 

 

 

notify每次只唤醒一个线程。

而notify唤醒线程是随机的，并不能保证每次唤醒的是异类线程，即生产者唤醒的可能是另一个生产者的线程。