Re: [Ocamlnet-devel] NetHTTPd/Netplex subtasking

[Gerd S. <in...@ge...>]

Am Donnerstag, den 10.01.2013, 15:17 +0100 schrieb Pierre-Alexandre
Voye:
> 
> 
> I followed one of the simpler example (don't remember which one), in
> fact, my app starts with this code :
> 
> let start handlers =
>   let (option_list, cmdline_infos) = Netplex_main.args() in
> 
> (*  .... cut ... *)
>  let nethttpd_factory =  Nethttpd_plex.nethttpd_factory
> ~handlers:handlers () in
>   Netplex_main.startup  ( Netplex_mp.mp ~keep_fd_open:true () )
>     Netplex_log.logger_factories  
>     Netplex_workload.workload_manager_factories 
>     [ nethttpd_factory ]          
>    cmdline_infos
> 
> 
> Normally, only the threads will use the object.

That's fine then.

> Because of my inability to user shared memory, I don't have any byte
> of global memory in this software (I use Memcache for that)
> 
> 
> So, if i start a thread and return the string result, is there a risk
> that the processes is killed by the master process before the thread
> finish his job (In theory not) ?

In theory and practice, this risk exists in deed. But you can do
something about it. The process is not killed with a signal, but there
is an orderly shutdown procedure going through several steps until
terminating the process, and it is possible to run some user code for
process cleanup. Nethttpd_plex.nethttpd_factory takes a ~hooks argument:

let hooks =
  object
    inherit Netplex_kit.empty_processor_hooks()

    method shutdown() = wait_for_the_termination_of_the_threads()
  end

I think a simple counter for the number of threads would be sufficient
(remember that "incr counter" and "decr counter" are atomic), and you
could just busy-wait (while !counter > 0 do sleep 1 done).

Note that there is also a second hook, pre_finish_hook, which is even
called later, but this hook is time-bound. If the maximum time is
exceeded, the process is finally killed (the timeout is set by
~terminate_tmo of Netplex_mp.mp).

Gerd

> 
> 
> 2013/1/10 Gerd Stolpmann <in...@ge...>
>         Am Donnerstag, den 10.01.2013, 13:19 +0100 schrieb
>         Pierre-Alexandre
>         Voye:
>         
>         >
>         > Can I use a thread without risk ?
>         
>         
>         Normally, yes, if you ensure that library functions do not
>         "see" that
>         there are several threads, i.e. any object is only used by one
>         thread at
>         a time. There are normally no mutexes controlling parallel
>         access
>         built-in (except where described). There are also no global
>         variables
>         making multi-threading impossible (and if so, there are
>         mutexes around
>         them).
>         
>         I must admit that I do not exactly understand your
>         architectural
>         problem. What I've got is that
>         
>          - You get a request via Nethttpd
>          - You call your service routine via the CGI-style interface
>          - that routine computes the result to return via CGI
>          - but that routine also needs to do some side work that is
>            not needed for the CGI return value, and could be run
>            outside the strict HTTP request/response cycle
>         
>         The answer to the question how you can run such side work
>         depends very
>         much on how you deploy Nethttpd. Do you use the Netplex
>         containers, or
>         did you follow one of the simpler examples?
>         
>         Gerd
>         
>         
>         
>         
>         --
>         ------------------------------------------------------------
>         Gerd Stolpmann, Darmstadt, Germany    ge...@ge...
>         Creator of GODI and camlcity.org.
>         Contact details:        http://www.camlcity.org/contact.html
>         Company homepage:       http://www.gerd-stolpmann.de
>         *** Searching for new projects! Need consulting for system
>         *** programming in Ocaml? Gerd Stolpmann can help you.
>         ------------------------------------------------------------
>         
> 
> 
> 
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-- 
------------------------------------------------------------
Gerd Stolpmann, Darmstadt, Germany    ge...@ge...
Creator of GODI and camlcity.org.
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
*** Searching for new projects! Need consulting for system
*** programming in Ocaml? Gerd Stolpmann can help you.
------------------------------------------------------------