Re: return to the begin of InputStream

On Thu, 10 Dec 2009 18:13:48 +0000, Tom Anderson wrote:


.......
 


Something about this niggled me - the effect of using coarse
(millisecond) time resolution and a fast (1.6 GHz) CPU when checking
the effect of single statements, so I rewrote your program to add 1000 mS
pauses between interesting groups of statements.

This shows that, on a Linux system anyway, the modification timestamp is
updated when a RandomAccessFile is written or a MappedByteBuffer is
changed. No other operations on an existing file including flushing its
buffers (FileDescriptor.sync() and MappedByteBuffer.force()) affect the
amended timestamp.

Here are the labelled timestamps:

$ java MMapTest
1 Create,open raf : = 1260562842000
2 Write : = 1260562843000
3 Sync : = 1260562843000
4 Mapped,put : = 1260562845000
5 Force : = 1260562845000
6 Close : = 1260562845000
7 Reopen raf : = 1260562845000
  File content : = Mapd file
8 Read : = 1260562845000
9 Close : = 1260562845000

and here's the modified code:

===============MMapTest.java===================

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
      
public class MMapTest
{
   public static void main(String[] args)
                      throws IOException, InterruptedException
   {
      File f = File.createTempFile("test", ".mmap");
      RandomAccessFile raf = new RandomAccessFile(f, "rw");
      showModTime(1, "Create,open raf ", f);
      raf.write("Test file\n".getBytes("UTF-8"));
      showModTime(2, "Write ", f);
      raf.getFD().sync();
      showModTime(3, "Sync ", f);
      FileChannel channel = raf.getChannel();
      MappedByteBuffer buf =
                       channel.map(MapMode.READ_WRITE, 0, f.length());
      buf.put("Mapd".getBytes("UTF-8"));
      showModTime(4, "Mapped,put ", f);
      buf.force();
      showModTime(5, "Force ", f);
      channel.close();
      showModTime(6, "Close ", f);
      raf = new RandomAccessFile(f, "r");
      showModTime(7, "Reopen raf ", f);
      System.err.println(" File content : = " + raf.readLine());
      showModTime(8, "Read ", f);
      raf.close();
      showModTime(9, "Close ", f);
   }
      
   private static void showModTime(int n, String label, File f)
                  throws InterruptedException
   {
      long t = f.lastModified();
      System.err.println(n + " " + label + ": = " + t);
      Thread.sleep(1000);
   }
}

===============MMapTest.java===================

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |