Java: Asynchronous concurrent writes to disk

Question

I have a function in my Main thread which will write some data to disk. I don't want my Main thread to stuck (High Latency of Disk I/O) and creating a new thread just to write is an overkill. I have decided to use ExecutorService.

ExecutorService executorService = Executors.newFixedThreadPool(3);

   Future future = executorService.submit(new Callable<Boolean>() {
    public Boolean call() throws Exception {
      logger.log(Level.INFO, "Writing data to disk");
      return writeToDisk();
    }
  });

writeToDisk is the function which will write to disk

Is it a nice way to do? Could somebody refer better approach if any?

UPDATE: Data size will be greater than 100 MB. Disk bandwidth is 40 MBps, so the write operation could take couple of seconds. I don't want calling function to stuck as It has to do other jobs, So, I am looking for a way to schedule Disk I/O asynchronous to the execution of the calling thread.

I need to delegate the task and forget about it!

Answer 1

There are two approaches that I am aware of, spin up a thread (or use a pool of threads as you have) or memory map a file and let the OS manage it. Both are good approaches, memory mapping a file can be as much as 10x faster than using Java writers/streams and it does not require a separate thread so I often bias towards that when performance is key.

Either way, as a few tips to optimize disk writing try to preallocate the file where possible. Resizing a file is expensive. Spinning disks do not like seeking, and SSDs do not like mutating data that has been previously written.

I wrote some benchmarks to help me explore this area awhile back, feel free to run the benchmarks yourself. Amongst them is an example of memory mapping a file.