SimulatedDiskIOServer.java

// Java - simulate occasional problematic (long blocking) requests for disk IO
// to build: javac SimulatedDiskIOServer.java
// to run: java SimulatedDiskIOServer

import java.net.*;
import java.io.*;
import java.text.*;
import java.util.*;


public class SimulatedDiskIOServer {

public static final int READ_TIMEOUT_SECS = 4;

public static final int STATUS_OK = 0;
public static final int STATUS_QUEUE_TIMEOUT = 1;
public static final int STATUS_BAD_INPUT = 2;


public static void simulated_file_read(long disk_read_time_ms) {
    try {
        Thread.sleep(disk_read_time_ms);
    } catch (InterruptedException ignored) {
    }
}

public static void handle_socket_request(Socket sock,
                                         long receipt_timestamp) {
    BufferedReader reader = null;
    BufferedWriter writer = null;

    try {
        reader =
            new BufferedReader(new InputStreamReader(sock.getInputStream()));
        writer =
            new BufferedWriter(new OutputStreamWriter(sock.getOutputStream()));

        // read request from client
        String request_text = reader.readLine();

        // did we get anything from client?
        if ((request_text != null) && (request_text.length() > 0)) {
            // determine how long the request has waited in queue
            final long start_processing_timestamp = System.currentTimeMillis();
            final long queue_time_ms = start_processing_timestamp -
                receipt_timestamp;
            final int queue_time_secs = (int) (queue_time_ms / 1000);

            int rc = STATUS_OK;
            long disk_read_time_ms = 0;
            String file_path = "";

            // has this request already timed out?
            if (queue_time_secs >= READ_TIMEOUT_SECS) {
                System.out.println("timeout (queue)");
                rc = STATUS_QUEUE_TIMEOUT;
            } else {
                StringTokenizer st = new StringTokenizer(request_text,",");
                if (st.countTokens() == 3) {
                    rc = Integer.parseInt(st.nextToken());
                    disk_read_time_ms = Long.parseLong(st.nextToken());
                    file_path = st.nextToken();
                    simulated_file_read(disk_read_time_ms);
                }
            }

            // total request time is sum of time spent in queue and the
            // simulated disk read time
            final long tot_request_time_ms =
                queue_time_ms + disk_read_time_ms;

            // return response text to client
            writer.write("" + rc + "," +
                         tot_request_time_ms + "," +
                         file_path + "\n");
            writer.flush();
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException ignored) {
            }
        }
        if (writer != null) {
            try { 
                writer.close();
            } catch (IOException ignored) {
            }
        }

        // close client socket connection
        try {
            sock.close();
        } catch (IOException ignored) {
        }
    }
}

public static void main(String[] args) {
    int server_port = 7000;
    try {
        ServerSocket server_socket = new ServerSocket(server_port);
        System.out.println("server listening on port " + server_port);

        while (true) {
            try {
                final Socket sock = server_socket.accept();
                if (sock != null) {
                    final long receipt_timestamp = System.currentTimeMillis();
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            handle_socket_request(sock, receipt_timestamp);
                        }
                    }).start();
                }
            } catch (IOException ignored) {
            }
        }
    } catch (IOException e) {
        System.out.println("error: unable to create server socket on port " + server_port);
    }
}

}