Terminating multiple processes

[Russel Winder]

On Wed, 2018-01-31 at 13:26 -0500, Steven Schveighoffer via
Digitalmars-d-learn wrote:
> 
[…]
> You talking about processes or threads? `receive` I believe is an 
> inter-thread channel, no?

These are threads with no shared memory, just message passing via
channels. I think of them as processes, but not OS processes. My poor
choose of names, I should just have said threads.

> Terminating processes is generally done via signals or in the case
> of 
> windows, calling the right system call.

Indeed. usually SIGHUP or SIGTERM, but never SIGKILL.

> Threads are another story. Typically, you need to have the thread
> check 
> periodically for a termination event. There's no "nice" way to do it
> out 
> of band.

This is what I was fearing. Of course from a theoretical standpoint it
is the right way to do things.

> In my experience, the best way to do it is to never block, but use
> some 
> sort of "wait on input" for any would-be-blocking operation. You can
> use 
> a large timeout, like 1 second, if immediate termination isn't
> important.

The thread in question is usually blocked in an inotify wait state
having no input channel. It seems I will have to manufacture a select.

I think this is what is missing in D, or at least my knowledge of it.
In Go, I can set up a select between channels and block, no need for a
timeout, an input on either channel causes a wakeup. The code then has
to work out which channel caused the wakeup. On the other hand DInotify
doesn't provide a channel style blocking wait, so select isn't an
option.

> If you are using Fibers, and all your i/o is done using some event-
> based 
> system (e.g. vibe.d), then things can be easier.

I am not sure I want to get into single-threaded event queues, but
maybe I should. I like the dataflow approach, it is simpler for me to
reason about.

-- 
Russel.
===========================================
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk
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