How to use mkdirs in a thread safe manner in Java?

Question

After experiencing issues with mkdirs() and poking around the interwebs, I get the impression that there are thread safety issues with mkdirs().

Is there a way to ensure the directories are properly created when it is possible that multiple threads might be trying to create similar file structures?

Thanks

(In my case I will be using this on Android)

Answer 1

I'm not sure if Android supports the concurrent package but here is my take:

private static Lock fsLock = new ReentrantLock();

private void mkdir( File dir ) throws FileNotFoundException {

    if( dir.exists() ) {
        return;
    }

    fsLock.lock();
    try {
        if( !dir.exists() ) {
            log.info( "Creating directory {}", dir.getAbsolutePath() );
            if( !dir.mkdirs() ) {
                throw new FileNotFoundException( "Can't create directory " + dir.getAbsolutePath() );
            }
        }
    } finally {
        fsLock.unlock();
    }
}

The method returns early if the directory already exists. If it doesn't exist, only one thread will try to create it.