Is there a real asynchronous file accessor in java?

Question

I want to read/write to a raw device(which is just a file in linux) asyncly, and I have been using java.nio.channels.AsynchronousFileChannel.

But it's a 'fake asynchronous', because the AsynchronousFileChannel uses a thread pool to execute the read/write tasks. It's actually calling the synchronized read/write interface offered by OS.

What I really want is a real asynchronous implementation which is io_submit in linux.

But I can't find it in jdk or any other repositories like guava or apache.

So my question is this :

In java, is there an existing implementation of asynchronous file accessor based on the native io_submit interface ?
If not, why can't I see anyone else who need it ?

Wouldn't this go against the very "platform-independent" nature of Java? — rmlan, May 02 '18 at 01:49
rmlan, there could be an asynchronous implementation which used io_submit on Linux and threads on platforms which didn't support that mechanism -- it doesn't have to break platform independence. — tgdavies, May 02 '18 at 02:20
Why do you want to do this? What will this allow you to do that `AsynchronousFileChannel` doesn't? — tgdavies, May 02 '18 at 02:21
Here's some discussion: http://mail.openjdk.java.net/pipermail/nio-discuss/2011-July/000581.html — tgdavies, May 02 '18 at 02:25
@tgdavies, thanks, I saw this discussion. But the reason I want this is that if I turn off the file system cache and the disk buffer, the threads' implementation can't give a good performance comparing to io_submit — T.Tony, May 02 '18 at 02:48

score 1 · Answer 1 · answered Sep 15 '19 at 19:15

In java, is there an existing implementation of asynchronous file accessor based on the native io_submit interface

Not in the default Java libraries at the time of writing (2019). I doubt there's much enthusiasm to implement an io_submit() Java wrapper in the default libraries because:

libaio/KAIO is quirky. Linux's KAIO is fraught with constraints like only really being asynchronous when doing direct I/O (and even then there are very elaborate rules which will turn submission synchronous if broken that go beyond the caller's control)
There's no guarantee that libaio library itself would be around so you would have to bundle it with Java or otherwise reimplement it.

If not, why can't I see anyone else who need it ?

People who need it that badly have recreated wrappers (e.g. see https://github.com/zrlio/jaio ). However supporting KAIO would be a Linux only thing and thus not that portable (which goes a bit against a key Java ethos).

Is there a real asynchronous file accessor in java?

1 Answers1