IO Exception - read end dead - what causes it in this example and how to fix it - multithread application in Java

问题:

This is an extension of my question posted here, while that seems to have fixed one part of my problem, now I see IO-Exception read end dead exception. I am using a multithreaded application where thread-1 produces random numbers and other thread-2 consumes it to calculate the average. once the average reaches a threshold, I signal thread-1 to stop producing the numbers. This is the basic design of the code.

I am getting IO-Exception read end dead exception. I want to know why it comes and how to fix it. Thanks.

The code below :

import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.PipedInputStream; import java.io.PipedOutputStream; import java.util.Random; import java.util.concurrent.atomic.AtomicBoolean;  //  class NumGen extends Thread {      PipedOutputStream pos;     DataOutputStream dos;     AtomicBoolean isDone;      public NumGen(PipedOutputStream pos,AtomicBoolean isDone){         this.pos=pos;         dos=new DataOutputStream(pos);         this.isDone=isDone;     }      public void run(){         while (!isDone.get()){             Random rand = new Random();             try {                 dos.writeDouble(rand.nextDouble()+100.0);             } catch (IOException e) {                 // TODO Auto-generated catch block                 e.printStackTrace();             }         }     } }  class RunningAvg extends Thread {      PipedInputStream pis;     DataInputStream dis;     Double avg;     int count;     Double runningTotal;     AtomicBoolean isDone;      public RunningAvg(PipedInputStream pis,AtomicBoolean isDone){         this.pis=pis;         dis=new DataInputStream(pis);         runningTotal=0.0;         avg=0.0;         this.isDone=isDone;     }      public void run(){         try {         while (dis.available()>0){             count+=1;             runningTotal+=dis.readDouble();                 avg=runningTotal/count;                 System.out.printf("The average in count no : %s is %s%n",count,avg);                 if (avg>1E5)                   isDone.set(true);         }             } catch (IOException e) {                 // TODO Auto-generated catch block                 e.printStackTrace();             }         }     }   public class InterThreadComm {      public static void main(String[] args){       try {         PipedOutputStream pos= new PipedOutputStream();         PipedInputStream pis = new PipedInputStream(pos);         AtomicBoolean isDone = new AtomicBoolean(false);         NumGen ng = new NumGen(pos,isDone);         RunningAvg ra = new RunningAvg(pis,isDone);         ng.start();         ra.start();     } catch (IOException e) {         // TODO Auto-generated catch block         e.printStackTrace();     }     }   } 

EDIT: As per the answer below: I tried to close the Streams using try-with-resources. but I get java.io.IOException: Pipe closed

public class InterThreadComm {      public static void main(String[] args){       try(PipedOutputStream pos= new PipedOutputStream();PipedInputStream pis =new PipedInputStream(pos)){          AtomicBoolean isDone = new AtomicBoolean(false);         NumGen ng = new NumGen(pos,isDone);         RunningAvg ra = new RunningAvg(pis,isDone);         ng.start();         ra.start();     } catch (IOException e) {         // TODO Auto-generated catch block         e.printStackTrace();     }     }   } 

回答1:

The root cause is here:

while (dis.available()>0){ 

What happens is the consumer thread is able to consume all of the data sometimes. There's nothing available so it breaks early.

The exception gets thrown because PipedInputStream/PipedOutputStream keep track of what threads are reading and writing. There is a private method called checkStateForReceive that throws, basically it is complaining that your consumer thread has ended:

} else if (readSide != null && !readSide.isAlive()) {     throw new IOException("Read end dead"); } 

(readSide is the consumer Thread.)

You can see this get called in the stack trace:

 java.io.IOException: Read end dead     at java.io.PipedInputStream.checkStateForReceive(PipedInputStream.java:246)     at java.io.PipedInputStream.receive(PipedInputStream.java:210)     at java.io.PipedOutputStream.write(PipedOutputStream.java:132)     at java.io.DataOutputStream.writeLong(DataOutputStream.java:207)     at java.io.DataOutputStream.writeDouble(DataOutputStream.java:242) 

So write calls receieve on the input stream, which calls checkStateForReceieve and throws if the reading Thread isn't alive.

I think your loop condition should just be:

while(!isDone.get()) { 

Unrelated to the exception, I also think you might have essentially an infinite loop here:

if (avg>1E5)     isDone.set(true); 

Your number generator generates numbers between 100 and 101 so averaging them will never be greater than 1e5. You might have meant to check if runningTotal > 1E5.

Also:

• Don't forget to close your streams when you are done with them.
• Your consumer thread catches IOException outside its loop but the producer catches inside the loop. The producer doesn't abort if there's an exception: it just keeps going, catching exceptions over and over. You might want to move the catch to outside the loop like the consumer.

About your edit:

If you want to close the streams in main, you can join on the threads.

try(     PipedOutputStream pos= new PipedOutputStream();     PipedInputStream pis =new PipedInputStream(pos) ){      AtomicBoolean isDone = new AtomicBoolean(false);     NumGen ng = new NumGen(pos,isDone);     RunningAvg ra = new RunningAvg(pis,isDone);      ng.start();     ra.start();      try {        ng.join(); // wait for ng and ra to complete        ra.join(); //     } catch(InterruptedException ie) {} } catch (IOException e) {     e.printStackTrace(); } 

文章来源: IO Exception - read end dead - what causes it in this example and how to fix it - multithread application in Java