vibe.d - asynchronously wait() for process to exit

[Steven Schveighoffer via Digitalmars-d-learn]

On 6/20/16 12:29 PM, Vladimir Panteleev wrote:
> On Monday, 20 June 2016 at 16:16:32 UTC, Steven Schveighoffer wrote:
>> What is the OS support for waitid
>> (http://man7.org/linux/man-pages/man2/waitpid.2.html)? Seems to have
>> support for async waiting of multiple processes (at least it can
>> return immediately if no child has exited). One consideration is how
>> responsive you need to be to a process exiting -- is it ok for example
>> to be notified 500ms after the process exits? If so, you can
>> interleave timed waits for socket data with a check to see if any
>> process exits. I've done this in the past for such things. I don't
>> know how well this works for libevent though.
>
> std.process has tryWait() if polling were acceptable, but I would really
> like to avoid it. Or have I misunderstood?

tryWait works on a single PID. From my reading of the docs, it appears 
you can call waitid and no matter how many children you have, if one 
exits, then it will capture that.

It would be nice if the Linux wait mechanisms were all standardized 
similar to Windows. I think the only thing that allows such universal 
access is file descriptors. Processes are definitely a case where it's 
not easy to deal with the events. Signal handlers suck as an async 
mechanism.

But my point was that you can poll on every start of event loop, and 
handle process exits if they are ready, and then every 500ms or so if no 
i/o becomes ready. In practice, this should be pretty responsive, unless 
you are only doing process execution and no i/o. And half second delay 
between process exit and handling of result is pretty small even in that 
case.

-Steve