Problem of using Pipe in threads

[Guy Jay]

Hello all,
I have encountered a "java.io.IOException: Write end dead" in the
following code:

    
import java.io.*;
import java.util.*;
 
public class MyPipe {
  
  private PipedWriter piOut;
  private PipedReader piIn;
  private PrintWriter out;
  private Timer timer;
  
public MyPipe() {
try {
piOut = new PipedWriter();
piIn = new PipedReader(piOut);
out = new PrintWriter(piOut, true);
} catch(Exception e) {
e.printStackTrace();
}
}

public void send() {
out.println("attack!");
}

public void cancelTimer() {
timer.cancel();
timer = null;
}


public void _main() {
MyRecv r = new MyRecv(piIn);
r.start();

timer = new Timer();
timer.schedule(new Attacker(this), 2000, 1000);

try {
while (true) {
out.println("send");
Thread.sleep(5000);
}
} catch(Exception e) {
e.printStackTrace();
}
}

public static void main(String[] args) {
new MyPipe()._main();
}

}
 
class Attacker extends TimerTask {

MyPipe p = null;

public Attacker(MyPipe p) {
this.p = p;
}

public void run() {
try {
p.send();
p.cancelTimer();
} catch(Exception e) {
e.printStackTrace();
}
}
}
 
class MyRecv extends Thread{
private PipedReader piIn;
private BufferedReader in;

public MyRecv(PipedReader piIn) {
try {
this.piIn = piIn;
in = new BufferedReader(piIn);
} catch(Exception e) {
e.printStackTrace();
}
}

public void run() {
try {
while (true) {
String line = in.readLine();
System.out.println("MyRecv: " + line);
}
} catch(Exception e) {
e.printStackTrace();
}
}
}

From my observation, whenever the timer thread is killed the pipe will be
automatically broken. What's the cause of this exception?
I ran the above code on java version "1.5.0_06" and Windows XP home sp2.
Thanks in advance.

[Peter Chase]

I'm not sure if your problem is the same as the one I had with PipedReader/Writer, but it might be, so I'll share it.

The documentation doesn't say so, but UTSL reveals that PipedReader/Writer expect exactly one thread to do the reading and one thread to do the writing. If one of those threads dies, it considers the pipe broken.

So, you can't do what I tried to do. I had a PipedReader open on one thread, connected to a PipedWriter. I tried to write snippets to the PipedWriter from various threads. But when the first writing thread died, so did my PipedReader/Writer.

[Henry Wong]

Never used PipedReader / PipedWriter, but for PipedInputStream / PipedOutputStream, it seems to keep track of only the last thread that read or write to the pipe. So...

When I got an IOException, due to a thread death on the other side of the pipe, I just waited until another thread used the other side of the pipe, and tried again. This worked because my threads rarely died, it only happened when the application changed users.

Henry

[Guy Jay]

Thank you very much.
Now i try to prevent killing the timer thread before the main thread using the pipe.