What is the difference between asynchronous I/O and asynchronous function?

Question

Node.js, is an asynchronous I/O. what does this actually mean?

Is there different between I create an async function by spawning another thread to do the process?

e.g.

void asyncfuntion(){
    Thread apple = new Thread(){
       public void run(){
           ...do stuff
       }
    }
    apple.start()
}

If there is difference, can I do a asynchronous I/O in javascript?

Answer 1

Asynchronous I/O

Asynchronous I/O (from Wikipedia)

Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished.

What this means is, if a process wants to do a read() or write(), in a synchronous call, the process would have to wait until the hardware finishes the physical I/O so that it can be informed of the success/failure of the I/O operation.

On asynchronous mode, once the process issues a read/write I/O asynchronously, the system calls is returned immediately once the I/O has been passed down to the hardware or queued in the OS/VM. Thus the execution of the process isn't blocked (hence why it's called non-blocking I/O) since it doesn't need to wait for the result from the system call, it will receive the result later.

Asynchronous Function

Asynchronous functions is a function that returns the data back to the caller by a means of event handler (or callback functions). The callback function can be called at any time (depending on how long it takes the asynchronous function to complete). This is unlike the synchronous function, which will execute its instructions before returning a value.

...can I do a asynchronous I/O in java?

Yes, Java NIO provides non-blocking I/O support via Selector's. Also, Apache MINA, is a networking framework that also includes non-blocking I/O. A related SO question answers that question.