Re: Basic question about LuaSocket and sleeping

[Matthew Wild <mwild1@...>]

Hi,

On 22 September 2012 16:52,  <mchalkley@mail.com> wrote:
> What I'm really wondering, though, is how socket reads take place. For
> example, I'm trying to keep my program from using any more system
> resources than possible because it's a monitoring tool, so it "sleeps"
> most of the time. How does LuaSocket handle reading sockets if I have
> it sleeping for 10-15 seconds between iterations (checking the
> schedule to see if there's anything to do). Does a packet that's
> received on a socket the program is listening to interrupt the sleep
> cycle, or what? This is such a basic question, I suppose, that it must
> be addressed in the documentation somewhere, but I can't find it...

The function you are looking for is select() (available as
socket.select()). It is basically a special kind of sleep from which
the process can be woken up by events on sockets:
http://w3.impa.br/~diego/software/luasocket/socket.html#select

There are libraries around to abstract select(), Copas is a really
nice one as far as simple programming goes, but it is designed more
for servers than clients. It does have the ability to make client
connections though, and add also timers, with a little more work. I'm
sure others here have other recommendations too.

> Maybe I'm just obsessing over something that's "automagic", but one of
> the reasons I'm learning Lua instead of using Perl or Python, which I
> already knew, is because of the speed and compactness of Lua. It's
> pretty cool to see something like what I've got right now run in less
> than 3 mb of memory (most of the time), and take about 5 seconds of
> cpu time every 24 hours....

I worked somewhere once where they ran a critical process on a server.
It occasionally crashed for one reason or another, so someone wrote a
small Ruby script to monitor the process and restart it when it
crashed. The next day both the process and the Ruby script were gone -
the simple Ruby script having somehow managed to consume all the
memory on the machine and bring down the service, and itself.

Regards,
Matthew