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
