Inter-Thread Communication. How to detect if one side is missing?

[Daniel B. Davis]

If this is the wrong forum -- sometimes its difficult to tell. I didn't notice a specific forum for inter-thread communication. Please forgive and move this to the correct place.

As part of inter-thread I/O for something I am doing, I have developed a working model of the I/O needed, attached. It uses PipedWriters and PipedReaders for bidirectional communication for two entities which I've named SideA and SideB in the model. The thing is, while SideA will always be present, SideB may not always be. SideB can be used independently, while SideA cannot be. Is there a way for SideB to tell if SideA is present using only the piping setup? Or must I use other ways for this?

A related question is that the Timeout has never worked, and I have not been able to make it. (Perhaps, instead I might use timers.) If it did, then sideB might use timeout and lack of response (the pipes block) to infer that sideA is missing. While there are plenty of ways to add other arrangements, doing it based upon the communication mechanism seems somehow more elegant.

Thanks, as always.

After trying to send a zip file for convenience, and got stopped by the website, I wonder: Often with my mailer I send a .zip file as .data, with instructions to rename. Is something like that welcomed here? I do not want to overstep, but sending zip can be a convenience. Not obviously for something small like this, but for larger things. Could it not be scanned for difficulties before execution? After that, I found I was also not permitted to send .txt files. Not knowing how you want files sent, I have tried 2 ways.

The file with extension .data is actually a .zip file containing only the src directory from eclipse. The file with extension .x is actually a text file containing all Java source, well-marked. Each contains only source for the 7 tiny files. Since the Attachment tab shows only the last file I attached, though it says I may attach 3, and the Firefox Windows File Chooser allows only single selection, I don't know what is going on. I would appreciate some words about how I might legitimately send 7 or more tiny source programs in three files. Should I copy them bodily into the text of the posting? Having written that, source is below:


File SideA.java
-----------------

package com.sideA;

// Bidirectional communications using 2 piped channels between two 
// separate notional class groupings files. subsystems, whathaveyou.
// Each of the channels are composed of 1 PipedReader and 1 PipedWriter.
// For symmetry, both SideA and SideB are identical but complementary:
// either one may be used to start things. Only SideA has been tested.

import java.io.*;
import java.util.*;
import com.sideB.SideB;
import com.sideB.SideBReceiver;
import com.sideB.SideBSender;
import com.sideA.SideASender;
import com.sideA.SideAReceiver;
import com.originator.Timeout;

public class SideA {
	//private static SideB sideB = null;
	//private static SideA sideA = null;
	//public SideA getSideA() { return sideA; }
	//public void setSideB (SideB sideB) { this.sideB = sideB; }

	public static void main(String[] args) throws Exception {
		
		new Timeout(1000, "\n\n>>>>>>>>>>>> Terminated <<<<<<<<<<<<<<<<\n");
		SideBSender bsender = new SideBSender();
		SideAReceiver areceiver = new SideAReceiver(bsender);
		SideASender asender = new SideASender();
		SideBReceiver breceiver = new SideBReceiver(asender);
		bsender.start();
		areceiver.start();
		asender.start();
		breceiver.start();
	}
} 

File SideASender.java
-------------------------

package com.sideA;

import java.io.*;
import java.util.*;
import com.sideB.SideB;
import com.sideB.SideBReceiver;
import com.sideB.SideBSender;
import com.originator.Timeout;

public class SideASender extends Thread {
	private Random rand = new Random();
	private PipedWriter out = new PipedWriter();
	public PipedWriter getPipedWriter() { return out; }
	
	private PipedWriter sideBWriter;
	
	public void run() {
		while(true) {
			for(char c = 'A'; c <= 'Z'; c++) {
				try {
					out.write(c);
					sleep(rand.nextInt(5));
				} catch(Exception e) {
					throw new RuntimeException(e);
				}
			}
		}
	}
}

File SideAReceiver.java
---------------------------

package com.sideA;

import java.io.*;
import java.util.*;
import com.sideB.SideB;
import com.sideB.SideBReceiver;
import com.sideB.SideBSender;
import com.originator.Timeout;

public class SideAReceiver extends Thread {
	StringBuffer sb = new StringBuffer();
	char c;
	private PipedReader in;
	
	public SideAReceiver(SideBSender bsender) throws IOException {
		in = new PipedReader(bsender.getPipedWriter());
	}
	
	public void run() {
		try {
			while(true) {
				// Blocks until characters are there:
				int i = 0;
				while(((c = (char)in.read()) != 0xa) && i++ < 15) {
					sb.append(c);
				}
				sb.append(c);
				System.out.println("SideA: "+sb.toString());
				sb.delete(0, sb.length());
			}
		} catch(IOException e) {
			throw new RuntimeException(e);
		}
	}
}

File SideB.java
-----------------

package com.sideB;

import java.io.*;
import java.util.*;
//import com.sideA.SideA;
import com.sideA.SideAReceiver;
import com.sideA.SideASender;
import com.originator.Timeout;

public class SideB {
	//private static SideA sideA = null;
	//private static SideB sideB = null;
	//public SideB getSideB() { return sideB; }
	//public void setSideA (SideA sideA) { this.sideA = sideA; }

	public static void main(String[] args) throws Exception {
		SideASender asender = new SideASender();
		SideBReceiver breceiver = new SideBReceiver(asender);
		SideBSender bsender = new SideBSender();
		SideAReceiver areceiver = new SideAReceiver(bsender);
		asender.start();
		breceiver.start();
		areceiver.start();
		bsender.start();
		new Timeout(4000, "Terminated");
	}
}

File SideBSender.java
-------------------------

package com.sideB;

import java.io.*;
import java.util.*;
import com.originator.Timeout;

public class SideBSender extends Thread {
	private Random rand = new Random();
	private PipedWriter out = new PipedWriter();
	public PipedWriter getPipedWriter() { return out; }
	
	private PipedWriter sideBWriter;
	
	public void run() {
		while(true) {
			for(char c = 'A'; c <= 'Z'; c++) {
				try {
					out.write(c);
					sleep(rand.nextInt(5));
				} catch(Exception e) {
					throw new RuntimeException(e);
				}
			}
		}
	}
}

File SideBReceiver.java
---------------------------

package com.sideB;

import java.io.*;
import java.util.*;
import com.sideA.*;

public class SideBReceiver extends Thread {
	StringBuffer sb = new StringBuffer();
	char c;
	private PipedReader in;
	
	public SideBReceiver(SideASender sender) throws IOException {
		in = new PipedReader(sender.getPipedWriter());
	}
	
	public void run() {
		try {
			while(true) {
				// Blocks until characters are there:
				int i = 0;
				while(((c = (char)in.read()) != 0xa) && i++ < 15) {
					sb.append(c);
				}
				sb.append(c);
				System.out.println("SideC: "+sb.toString());
				sb.delete(0, sb.length());
			}
		} catch(IOException e) {
			throw new RuntimeException(e);
		}
	}
}

File Timeout.java
-------------------

package com.originator;
import java.util.*;
import javax.naming.TimeLimitExceededException;

public class Timeout  implements Runnable {
	String msg;
	long wait;
	
	public Timeout(int interval, String msg) {
		wait = interval;
		this.msg = msg;
		new Thread().start();
	}
	
	public void run() {
		try{
			Thread.sleep(wait);
			//System.out.println(msg);
			//System.exit(0);
			throw new TimeLimitExceededException(msg);
		} catch(TimeLimitExceededException tlx) {
			System.out.println(tlx.getMessage());
			System.exit(0);
		} catch(InterruptedException intx) {
			intx.printStackTrace();
		}
	}

}

[Tony Docherty]

Please UseCodeTags (← click) when posting code as it makes it easier for people to read your code. I've added them for you this time.