Mongrel users - Apr 2007 - What''s mongrel doing when it''s idle.

A totally idle mongrel seems to wake up about once a second doing
a little stuff like:
   select(4, [3], [], [], {0, 999696})     = 0 (Timeout)
   gettimeofday({1176400534, 112594}, NULL) = 0
   select(4, [3], [], [], {0, 0})          = 0 (Timeout)
   time(NULL)                              = 1176400534
   time(NULL)                              = 1176400534
   gettimeofday({1176400534, 113841}, NULL) = 0
   gettimeofday({1176400534, 114138}, NULL) = 0
over and over.

I realize it''s not a big deal to do so little so infrequently; but 
wondering why it wakes up to do anything at all.    Any reason
whatever it''s polling for can''t just be added to the select()
conditions?


I only noticed because on an extremely overloaded server (I have dozens of 
virtual machines running on a box here and memory on each is limited and 
each are running quite a few web servers) I was mildly surprised to see 
that the mongrel tasks didn''t get swapped out completely.  The waking
up
once a second is probably why.

    Ron

PS: Equally curious to me as that irb seems to wake up a few times a 
second too; but that''s less of a concern because I don''t leave
irbs
running on purpose.

On Thu, 12 Apr 2007 11:03:36 -0700 (PDT)
rm_mongrel at cheapcomplexdevices.com wrote:
> 
> A totally idle mongrel seems to wake up about once a second doing
> a little stuff like:
>    select(4, [3], [], [], {0, 999696})     = 0 (Timeout)
>    gettimeofday({1176400534, 112594}, NULL) = 0
>    select(4, [3], [], [], {0, 0})          = 0 (Timeout)
>    time(NULL)                              = 1176400534
>    time(NULL)                              = 1176400534
>    gettimeofday({1176400534, 113841}, NULL) = 0
>    gettimeofday({1176400534, 114138}, NULL) = 0
> over and over.
> 
> I realize it''s not a big deal to do so little so infrequently; but
> wondering why it wakes up to do anything at all.    Any reason
> whatever it''s polling for can''t just be added to the
select()
> conditions?
Ruby uses select() to do it''s IO processing and thread control, but
only after you start one thread.

Ruby doesn''t put a timeout parameter into the select call unless
there''s a thread sleeping.

If you have threads waiting for IO, and have someone running Mongrel
from the console, and you don''t have a thread calling sleep once a
second, then...

CTRL-C won''t exit the process on most systems.

So, most ruby code that uses threads throws in a bogus sleeping thread
that doesn''t do much.

-- 
Zed A. Shaw, MUDCRAP-CE Master Black Belt Sifu
http://www.zedshaw.com/
http://www.awprofessional.com/title/0321483502 -- The Mongrel Book
http://mongrel.rubyforge.org/