locking a file from processing

[Andrew Mcmurray]

Hi all

I have multiple processes monitoring the same directory for files to process. I want to be able to lock a file that is being processed so none of the other processes can start processing that file. I have seen methods that rename the file with '.' in front. Is this a good way to do it or is there a better way? Also when you rename do you create a new file?

Thanks,

AMD

[Peter Chase]

I don't think there's anything special about renaming with a dot in front of the name, except that some platforms will hide that file from ordinary directory listings presented to the user. They will not be hidden from Java, I believe, even on those platforms.

However, if your programs "know" that a file starting with a dot is already being processed, then your idea ought to work, providing that renaming is "atomic", meaning no thread or process will see a part-renamed file.

Unfortunately, the Java API does not make any guarantees about how renaming (File.renameTo()) works. It might be atomic, or it might not.

In practice, I believe that renaming, within the same directory is atomic on Win/Lin/MacOSX. Therefore, your idea should work.

[Peter Chase]

... but a nicer architecture might be to have a single component responsible for scanning the directory. That component would then hand over responsibility for processing the files to one of a pool of processor components.

[Andrew Mcmurray]

Thanks Peter,

So should I do something like this

    
File file = new File("oldname"); 
File file2 = new File(".newname"); 
       
boolean success = file.renameTo(file2); 
if (!success) 
{ 
         // File was not successfully renamed 
} 
 

Or can I just use file.rename on the original file?

Thanks,

AMD