Question

I have a homework assignment to create a simple data transfer mechanism with a client/server TCP socket pair by redirecting standard I/O. I actually have it working, but when I try to transfer large files (say ~5g) the speed slows down dramatically. I am using BufferedInputStream and BufferedOutputStream, and I think that perhaps there is some optimization I can make there. The code for my server is:

private static final int BUF_SIZE = 2047;

public static void main(String[] args) throws IOException{
   /*
    * Attempt to parse command line arguments.
    * @require args[0] is an int
    */
   int port = 0;
   try {
       port = Integer.parseInt(args[0]);
   } catch(NumberFormatException e) {
       System.err.println("Port must be an integer in range 0 - 65535.");
       System.exit(-1);
   }

   /*
    * Bind server socket to specified port number and wait for request.
    * @require port >= 0 && port <= 65535
    */
   ServerSocket welcomeSocket = null;
   welcomeSocket = new ServerSocket(port);
   System.out.println("Now listening on port: " + port);

    /*
     * Accept connection from client socket.
     */
    Socket connectionSocket = null;
    connectionSocket = welcomeSocket.accept();
    System.out.println("Client made connection");

    BufferedInputStream input;
    BufferedOutputStream output;
    if(System.in.available() > 0) {
        input = new BufferedInputStream(System.in, BUF_SIZE);
        output = new BufferedOutputStream(
                connectionSocket.getOutputStream(), BUF_SIZE);
    } else {
        input = new BufferedInputStream(
                connectionSocket.getInputStream(), BUF_SIZE);
        output = new BufferedOutputStream(System.out, BUF_SIZE);
    }

    int place;
    while((place = input.read()) != -1)
        output.write(place);

    input.close();
    output.close();
    welcomeSocket.close();
    connectionSocket.close();
}

The client code is essentially the same. I have tried using different buffer sizes, including the default (by not specifying a buffer size), but they are all running at approximately the same speed. Any pointers on how I can increase my performance?

Thank you for your time!

Answer 1

while((place = input.read()) != -1)

You’re reading one byte at a time from the buffer. The overhead of calling this method millions of times is rather large.

I would suggest reading more than one byte into a buffer with the other version (and writing the same way):

public int read(byte[] b,
            int off,
            int len)

Example:

byte[] myBuffer = new byte[BUF_SIZE];
while((place = input.read(myBuffer, 0, BUF_SIZE)) != 1)
    output.write(myBuffer, 0, place);