communication between worker processes

[Maxim Dounin]

Hello!

On Mon, Oct 19, 2009 at 05:18:12PM -0400, Leo P. wrote:

> Maxim Dounin wrote:
> >Hello!
> >
> >On Mon, Oct 19, 2009 at 12:23:00AM -0400, Leo P. wrote:
> >
> >>How might I be able to send a message or (custom) event to some
> >>given worker process? I am storing pointers to requests (and the
> >>workers that processed them) in shared memory for a module (
> >>http://github.com/slact/nginx_http_push_module ), and need to alert
> >>said workers to respond to said requests, from the context of a
> >>location request handler in a module. (maybe using ngx_channel
> >>stuff?)
> >>I'd really appreciate any suggestions.
> >
> >There is no infrastructure for interprocess notifications in nginx
> >right now.  Basically it's the reason why there is no such things
> >as busy locks and so on.
> >
> >You may try to emulate it via e.g. message queue in shared memory
> >and periodic timer in each worker process to check it.  It's not
> >perfect, but probably will work for you.
> >
> >Maxim Dounin
> >
> >
> What about using ngx_add_channel_event on process initialization?
> Is there anything obviously wrong with doing something like the following:
> 
> /*in init process callback*/
>    ngx_socket_t my_channel=ngx_channel;
>    /* is that the correct socket? what about
>      ngx_processes[ngx_process_slot].channel[0] and
>      ngx_processes[ngx_process_slot].channel[1] ?
>      which could be used?
>    */

[...]

Socket pairs in question are used for nginx's own needs (control 
commands from master to workers).  Any attempt to reuse them will 
case nginx malfunction at next control command.

Eventually this will grow into something more generic and modules 
will be able to use this for their own commands.  But it's not here 
yet.

Maxim Dounin

p.s. BTW, just to make sure you know: nginx_http_push_module 
relies on shared memory as something unconditionally available for 
all processes, but this isn't really true during binary upgrades.  
New binary creates their own shared memory zones from scratch.  As 
a result - module won't survive binary upgrades flawlessly but 
will loose messages instead.