Re: Basic question about LuaSocket and sleeping

[mchalkley@...]

Saturday, September 22, 2012, 2:01:56 PM, you wrote:

>> -----Original Message-----
>> From: lua-l-bounces@lists.lua.org [mailto:lua-l-bounces@lists.lua.org]
>> On Behalf Of mchalkley@mail.com
>> Sent: zaterdag 22 september 2012 18:33
>> To: Lua mailing list
>> Subject: Re: Basic question about LuaSocket and sleeping
>> 
>> Matthew,
>> 
>> Saturday, September 22, 2012, 12:11:19 PM, you wrote:
>> 
>> > 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
>> 
>> Thanks!  I'll play with a test using select() instead of sleep(), and
>> learn how that works...

> Select takes a list of sockets to write to and a list of sockets to read
> from. The OS blocks the thread (no CPU usage) until the select times out or
> one of the listed sockets becomes available for reading/writing (that is:
> guaranteed not to block when performing the next read/write, though there
> are exceptions). This allows you to wait for incoming IO without using CPU.

> Select isn't very hard, but check the part about the timeouts on the sockets
> and the select (2 different timeouts). I usually put sockets on 0 timeout
> (non-blocking) and set the required timeout be used with select.
> For an implementation using timers with a scheduler checkout CopasTimer
> (available through LuaRocks). It extends Copas with timer capabilities using
> calculated timeouts (when it calls select, it sets the timeout to the first
> timer expiring, so it returns upon IO or when a timer is due to be
> executed). 
> Though Copas is essentially a server (waits for incoming connections), it's
> simple to add outgoing connections. I think the method is called addtask()
> or newtask() or something similar. The Copas documentation (on github,
> master, not released yet) contains an example I added a while ago. Dunno
> what you need, but UDP support is also in master, not released yet.

> HTH.

> Thijs

Yes, it does help - I appreciate the info. In fact, I think I'll play
with Copas first, before I actually put the functionality into my
program. I'm trying to do most of this stuff myself, so I understand
how it (and Lua) really works, and so I know I'm really not adding
more than what I really need, but I also realize the benefits of not
reinventing the wheel when I don't have to...

Thanks again,

Mark