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();
}

来源：https://stackoverflow.com/questions/22181107/io-exception-read-end-dead-what-causes-it-in-this-example-and-how-to-fix-it

标签

java

multithreading

ioexception