IO Handling Problem

[sonalim]

Hi,

I'm in a big mess and kindly need your advices(and it's kind of urgent too)..

I have written a Named Pipe client in java where the Named Pipe server is in C++ and cannot be modified. In the client, i have used java's "RandomAccessFile" to create a bidirectional pipe to the server.

From another class a separate thread is continuously trying to read the Named Pipe Client where the main thread tries to write to the Named Pipe Client when required.

In the ideal situation i want the Named Pipe Client's read method to return -1 or null when there in no incoming stream from the server and sleep for 100ms (which will allow the main thread to perform write operations if required) and then go for the next iteration of listening. Or at-least implementing a timeout for the read function is required.

I can not change the server/client communication to sockets since server is already implemented in C++ and can not be altered.

Please give me a hit to solve this...
Thanks!

[keang]

Please can you show the relevant bits of your code.

[sonalim]

This is the code segment which create the pipe

private RandomAccessFile rafPipe = null;
....
//create the pipe
try {
	rafPipe = new RandomAccessFile( pipeName, "rws");
} catch (FileNotFoundException e) {
	System.out.println("FileNotFound exception while creating the pipe...");
	e.printStackTrace();
}

This is the write function

public boolean write(byte[] m_pTxDataBuffer, short totalpktLength) { 
	boolean wSuccess = false;
	//m_pTxDataBuffer is a pointer to the buffer that contains data to be written
	if(totalpktLength<0){
		totalpktLength = 0;
	}
	try {
		rafPipe.write(m_pTxDataBuffer, 0, totalpktLength);
		wSuccess = true;
	}catch (IOException e){
		System.out.println("IOException while writing to the pipe...");
		e.printStackTrace();
	}
	return wSuccess;
}

This is the read function

public int Read(byte[] pchBuff, int inBufferSize) {
	int byteTransfer = 0;
	if(inBufferSize<0){
		inBufferSize = 0;
	}
	try {
		byteTransfer = rafPipe.read(pchBuff, 0, inBufferSize);
	}catch (IOException e) {
		System.out.println("IO Exception while reading from the pipe.");
		e.printStackTrace();
	}
	return byteTransfer;
}

[J-Ideas]

i am thinking of if nothing in inputstream, sleep for 100ms, this is if your read is in a seperate thread from your write


if(Inputstream.available()==0) Thread.sleep(100);

[keang]

Use the getChannel() method to get a FileChannel which can be read from without blocking.

If you are reading and writing to the same file on separate threads you may also want to implement some form of locking to ensure the read thread doesn't attempt to read whilst a write is taking place.

[sonalim]

Hi,

Finally I managed to improve the code to avoid it from getting blocked until at-least one byte is read from its read() method. To implement that, before entering I check the length() of the pipe by invoking

rafPipe.lengthz()

, if the value returned is greater than "0", I invoke the read() method or otherwise avoid it. Likewise I managed to overcome the undesirable state arose because of using RandomAccessFile to implement a bidirectional named pipe.

Thanks for all your comments . I tried all of it, but finally only this method, worked for me..