Power failure and FileOutputStream behavior.

Question

Hi,
In our application, we use FileOutputStream to write binary data to a file. We perform a out.close() to close the file. However, if there is a power failure, the data is not written out.
We created a simple test utility, which writes out 1K file containing 256 sequences of the string 'abcd'. After the close, we did a sleep(60000) to sleep for a minute. Everything works fine in the normal case. If however there is a power failure (pull the power cord), after the close() but before the sleep() expires, the file is not written out. We get a file of either zero bytes or sometimes a file of 1024 bytes, all of them being zero. The JVM sis the SUN JVM 1.4.3_08
The following is a simple class.
import java.io.File;
import java.io.FileOutputStream;
public class FileWriteTest {
     public static void main(String args[]) {
          if (args.length < 1) {
               System.err.println("Usage: <file> <wait-time>");
               return;
          final String filename = args[0];
          final byte[] buffer = new byte[1024];
          int waitTime = 60 * 1000;
          if (args.length == 2)
               waitTime = Integer.parseInt(args[1]);
     for (int i = 0; i < 256; i++) {
               buffer[i * 4 + 0] = 'a';
               buffer[i * 4 + 1] = 'b';
               buffer[i * 4 + 2] = 'c';
               buffer[i * 4 + 3] = 'd';
     try {
                    java.io.OutputStream out = new FileOutputStream(new File(filename));
                    out.write(buffer, 0, buffer.length);
                    out.close();
                    Thread.sleep(waitTime);
          } catch (Exception e) {
               System.err.println("Exception: " + e.getLocalizedMessage());
               e.printStackTrace();
               return;               
Thanks.

Answer 1

FileOuputStream doesn't do any buffering so what you are seeing is the behaviour of your operating systems. They usually defer writes so they can be consolidated and performed at convenient times for the disc controller.