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From: cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups: comp.unix.programmer
Subject: Re: OT: Windows (Was: Re: Open Source does not mean easily
Date: Mon, 6 Jan 2025 16:39:49 -0000 (UTC)
Organization: PANIX Public Access Internet and UNIX, NYC
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In article <vlgun1$1minf$1@dont-email.me>,  <Muttley@DastardlyHQ.org> wrote:
>On Mon, 6 Jan 2025 15:22:51 -0000 (UTC)
>cross@spitfire.i.gajendra.net (Dan Cross) wibbled:
>>In article <vlgots$1le5s$1@dont-email.me>,  <Muttley@DastardlyHQ.org> wrote:
>>>In Windows yes, which frankly is probably not a coincidence. Not so much
>>>in unix unless you're writing a GUI program.
>>
>>Very much in Unix, actually.  The kernel is highly asynchronous
>>(it must be, to match the hardware), and has been since the
>>early 1970s.  Many user programs similarly.
>>
>>Historically, many systems have provided direct support for
>>asynchronous programming on Unix.  Going back to the early
>>commerical Unix days, masscomp's real time Unix had ASTs, not
>>signals, to support asynch IO directly from userspace.  More
>>recently, POSIX.1b and POSIX AIO are widely supported.  Polling
>>interfaces like kqueue and epoll, etc, exist largely to support
>
>Multiplexing is not asychronous, its simply offloading status checking to
>the kernel.

Of course.  It's a means to allow a program to respond to
asynchronous events.

>The program using is still very much sequential , at least at
>that point.

But the events are not.  That's the point.  This allows a
program to initiate a non-blocking IO operation (like, say,
establishing a TCP connection using the sockets API), go do
something else, and check it's status later.

>Posix AIO is not asynch in the strict sense , its more "ok kernel, go do this
>and I'll check how you're doing later". Proper asynch where the program 
>execution path gets bounced around between various callbacks is something
>else entirely.

The POSIX AIO interface allows the kernel to generate a signal
to inform the program that an IO operation has completed, e.g.,
by setting up the `aio_sigevent` and `SIGEV_SIGNAL`.  It doesn't
get much more asynchronous than that.

	- Dan C.