(fs) Cannot delete file if memory mapped with FileChannel.map (windows)

Name: nt126004 Date: 07/15/2002


FULL PRODUCT VERSION :
java version "1.4.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-b92)
Java HotSpot(TM) Client VM (build 1.4.0-b92, mixed mode)

FULL OPERATING SYSTEM VERSION : Microsoft Windows 2000
[Version 5.00.2195]


A DESCRIPTION OF THE PROBLEM :
A file opened for read-only access and memory mapped using
the map method of FileChannel cannot be deleted even when
the channel is closed.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1.Compile and run the source code
2. Run it as follows: java testFileDelete filename
   where filename is the name of the file to be deleted.


EXPECTED VERSUS ACTUAL BEHAVIOR :
Expected: List the contents of the file specified on the
command line and delete it.
Actual: Lists the contents of the file, however fails to
delete it.


ERROR MESSAGES/STACK TRACES THAT OCCUR :
Could not delete file testdel.txt

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;

public class testFileDelete {

public static void main(String[] args) {


FileInputStream fis = null;

if (args.length < 1) {
System.err.println("Usage: java testFileDelete <filename>");
System.exit(1);
}

File f = new File(args[0]);


try {
// Open the file
fis = new FileInputStream(f);
} catch (FileNotFoundException ex) {
System.err.println("Error! " + ex.getMessage());
System.exit(2);
}


try {
// Get a channel from the stream
FileChannel fc = fis.getChannel();

// Map the file into memory
MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, (int)fc.size());

// Do something interesting here. For this example, just print the
// contents of the file.

// Decode the file into a char buffer, so we can print the contents.
Charset cs = Charset.forName("8859_1");
CharsetDecoder cd = cs.newDecoder();
CharBuffer cb = cd.decode(bb);

// Now print it out to standard output
System.out.print(cb);

// Close the channel and the stream
fc.close();

// Close the input stream even though closing the
// channel should do this
fis.close();
} catch (IOException ex) {
System.err.println("Error! " + ex.getMessage());
System.exit(3);
}

// Done processing file. Now delete it.
boolean deleted = f.delete();
if (!(deleted)) {
System.err.println("Could not delete file " + f.getName());
System.exit(2);
}
}

}
---------- END SOURCE ----------

CUSTOMER WORKAROUND :
FileChannel.map seems to be causing this problem. A
possible workaround is to not use the NIO package.
(Review ID: 153724)
======================================================================

Name: nt126004 Date: 07/15/2002


FULL PRODUCT VERSION :
java version "1.4.0"
Java(TM) 2 Runtime Environment, Standard Edition (build
1.4.0-b92)
Java HotSpot(TM) Client VM (build 1.4.0-b92, mixed mode)

FULL OPERATING SYSTEM VERSION :
Microsoft Windows 2000 [Version 5.00.2195]

A DESCRIPTION OF THE PROBLEM :
If a file has been memory mapped (using
java.nio.channels.FileChannel.map), File.deleteOnExit does
not work reliably. It depends on whether the mapped buffer
has been 'finalized' before the JVM exits.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Run the attached code. You have a 1KB 'temporary' file
left behind.
2. If you uncomment the System.gc() line, the subsequent
delete may work (but in my actual code this is unreliable).


EXPECTED VERSUS ACTUAL BEHAVIOR :
I would expect the File.deleteOnExit to always delete the
file. This would require the JVM to unmap any mapped files
before deleteing 'temporary' files. This failure I consider
a bug.

There is a second issue, which is the difficulty of using
File.delete and other methods when we can't control the
timing of unmapping. I will submit a separate RFE for this.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.*;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

class TestMemoryMapping
{
public static void main(String[] args)
{
try
{
File f = File.createTempFile("Test", null);
f.deleteOnExit();
RandomAccessFile raf = new RandomAccessFile(f, "rw");
raf.setLength(1024);
FileChannel channel = raf.getChannel();
MappedByteBuffer buffer = channel.map
(FileChannel.MapMode.READ_WRITE, 0, 1024);
channel.close();
raf.close();
buffer = null;
// System.gc();
if (f.delete())
System.out.println("Temporary file
deleted: "+f);
else
System.out.println("Not yet deleted: "+f);
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}
---------- END SOURCE ----------

CUSTOMER WORKAROUND :
Calling System.gc sometimes works.
(Review ID: 153921)
======================================================================