FileEditor.java - I/O Intensive Process

JVM Tutorials - Herong's Tutorial Examples

∟I/O Impact of Multi-Thread Applications

∟FileEditor.java - I/O Intensive Process

This section describes a thread productivity testing program, FileEditor.java, that repeats a work unit of reading data from a file and writing it back. It is a good example of I/O intensive process.

After looking at the CPU usage impact of multi-thread CPU intensive applications, we can now look at the disk I/O usage impact of multi-thread I/O intensive applications.

Here is the source code of FileEditor.java, which represents a thread to read data from a file and write it back repeatedly:

/* FileEditor.java
 * Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
import java.io.*;
import java.util.*;
public class FileEditor extends Thread {
   public int fileSize; // The size of the file to work on
   public String fileName; // The name of the file
   public long jobCount; // The number of jobs done so far
   public int myCheckSum; // The checksum of the file
   public int firstByte; // The first byte of the file
   public static void main(String[] a) {
      int size = 1000;
      String name = "FileEditor.dat";
      long interval = 1; // Monitoring interval in seconds
      if (a.length>0) size = Integer.parseInt(a[0]);
      if (a.length>1) name = a[1];
      System.out.println("File size: "+size);

      // Initializing the data file
      byte[] data = new byte[size];
      Random r = new Random();
      r.nextBytes(data);
      try {
         FileOutputStream fos = new FileOutputStream(name);
         fos.write(data);
         fos.close();
      } catch (Exception e) {
      	 System.out.println(e.toString());
      	 return;
      }
      
      FileEditor t = new FileEditor(size, name);
      t.start();
      int i = 0;
      long startTime = System.currentTimeMillis();
      System.out.println(
         "Time, Count, Productivity, CheckSum, firstByte");
      while (true) {
         try {
            sleep(interval*1000);
         } catch (InterruptedException e) {
            System.out.println("Monitor interrupted.");
         }
         long curTime = System.currentTimeMillis();
         long duration = (curTime - startTime)/1000;
         long productivity = t.jobCount/duration;
         System.out.println(duration+", "+t.jobCount
            +", "+productivity+", "+t.myCheckSum+", "+t.firstByte);
      }
   }
   public FileEditor(int size, String name) {
      fileSize = size;
      fileName = name;
      jobCount = 0;
      myCheckSum = 0;
      firstByte = 0;
   }
   public void run() {
      byte[] buffer = new byte[fileSize];
      try {
         while (true) {
            FileInputStream fis = new FileInputStream(fileName);
            int bytes = fis.read(buffer);
            fis.close();
            long sum = 0;
            for (int i=0; i<fileSize; i++) {
                sum = (sum+(buffer[i]&0x00FF))%Integer.MAX_VALUE;
            }
            myCheckSum = (int)sum;
            firstByte = buffer[0]&0x00FF;
            FileOutputStream fos = new FileOutputStream(fileName);
            fos.write(buffer,1,fileSize-1);
            fos.write(buffer,0,1);
            fos.close();
            jobCount++;
         }
      } catch (Exception e) {
      	 System.out.println(e.toString());
      	 return;
      }     
   }
}

Some notes on FileEditor.java:

FileEditor.java is designed as a Thread class, so it can be invoked as multithreading processes by a controlling program.
The run() method is designed to perform the work unit repeatedly in the endless while loop.
The work unit is to open a data file, read its data, and write the data back with 1 byte shifted. Not much memory is needed. Not much CPU power is needed. And no database operations.
The main() method is designed to run the process as a single thread to verify the correctness of the process.

FileEditor.java seems to be working correctly, as you can see from the following test results. It shows that 4 random bytes were used in the data file: 78, 39, 230, 197, and the sum is 544.

C:\>"\Program Files\java\jdk1.7.0_45\bin\javac" FileEditor.java

C:\>"\Program Files\Java\jdk1.7.0_45\bin\java" FileEditor 4
File size: 4
Time, Count, Productivity, CheckSum, firstByte
1, 3104, 3103, 544, 230
2, 5760, 2880, 544, 197
3, 7415, 2471, 544, 230
4, 10133, 2533, 544, 78
5, 13557, 2711, 544, 78
6, 15178, 2529, 544, 39
7, 18899, 2699, 544, 230
8, 20687, 2585, 544, 230
9, 23472, 2608, 544, 197
10, 26679, 2667, 544, 230
11, 30381, 2761, 544, 197
12, 32760, 2730, 544, 197
13, 36462, 2804, 544, 39
14, 38472, 2748, 544, 197
15, 40940, 2729, 544, 197
16, 44014, 2750, 544, 39
...

But when running it again with a file size of 10, I got an exception:

C:\>"\Program Files\Java\jdk1.7.0_45\bin\java" FileEditor 10
java FileEditor 10
File size: 10
Time, Count, Productivity, CheckSum, firstByte
1, 832, 832, 1472, 99
2, 2273, 1136, 1472, 136
3, 3959, 1319, 1472, 102
4, 5674, 1418, 1472, 129
5, 6716, 1343, 1472, 94
6, 8357, 1392, 1472, 231
7, 9337, 1333, 1472, 231
8, 10794, 1349, 1472, 129
9, 11877, 1319, 1472, 231
10, 12827, 1282, 1472, 231
...
43, 55835, 1298, 1472, 94
44, 56922, 1293, 1472, 99
45, 58131, 1291, 1472, 218
java.io.FileNotFoundException: FileEditor.dat (The requested 
operation cannot be performed on a file with a user-mapped section
open)

What's wrong with FileEditor.java? I am reading and writing to the same file repeatedly. But it is always closed before open it again. See next section for more details on this issue.

Last update: 2014.

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Downloading and Installing JDK 1.8.0 on Windows

Downloading and Installing JDK 1.7.0 on Windows

java.lang.Runtime Class - The JVM Instance

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ClassLoader Class - Class Loaders

Class Class - Class Reflections

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JRockit JVM 28.2.7 by Oracle Corporation

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