FileChannel and mapping files

Question

Hello,
I'have some strange problem with mapping file using a FileChannel and the map method.
My program creates some number of threads. These threads are accessing in a file (in a different places) to write down some information. The number of the created threads is about (max) 100 but at one moment I may have for example from 1 to 60 threads that are active.
Sometimes when a thread tries to map some region from the file, I have an exception.
So here is my code:
FileChannel fch = rafOut.getChannel();
try {
position = rafOut.getChannel().position();
//I have the exception here fch.map(....)
mbf = fch.map(FileChannel.MapMode.READ_WRITE, position, Manager.getSize());
} catch (IOException e2) {
  e2.printStackTrace();
//here I'm using some putXXX() methods
//and at the and I have
mbf.force();
}This code sometimes generates this exception:
java.io.IOException: The requested operation over a mapped file was not accomplished
     at sun.nio.ch.FileChannelImpl.truncate0(Native Method)
     at sun.nio.ch.FileChannelImpl.map(Unknown Source)
     at DataWriter.run(DataWriter.java:40)
Any idea why I have this error?
Regards,
Anton
PS. The first part of the exception message was written in French, so I tried to translated it :)
Edited by: anton_tonev on Nov 5, 2007 6:49 AM

Answer 1

Hi ejp,
i'm trying to extend the file. In the begging the file is empty, so every thread adds data to the file.
About the mapping, yes I know that map many times the same file is not the right solution ... but for every thread I'm mapping a different part of the file, for exemple :
one thread maps from 0 byte to the 256 byte and writes there the data.
another thread maps from 256 to 1024 and so on ...
The problem is that the threads don't know the size of the data before the mapping(e.g. the future size of the entire file), if it was known, may be I could map the entire file in the memory. And there is more thing, the file sometimes becomes very big .. a hundred of Gbs, so mapping just some parts of it in the memory for me is the best solution.
Regards,
Anton