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?
*/
if (ngx_add_channel_event(cycle, my_channel, NGX_READ_EVENT,
ngx_http_push_channel_handler) == NGX_ERROR) {
exit(2);
}
//...

#define NGX_CMD_HTTP_PUSH_CHECK_MESSAGES 87; //some unlikely number.
(looks hacky)

static void ngx_http_push_channel_handler(ngx_event_t *ev) {
//mostly copied from ngx_channel_handler (os/unix/ngx_process_cycle.c)
ngx_int_t n;
ngx_channel_t ch;
ngx_connection_t *c;
if (ev->timedout) {
ev->timedout = 0;
return;
}
c = ev->data;
for ( ;; ) {
n = ngx_read_channel(c->fd, &ch, sizeof(*ch), ev->log);
if (n == NGX_ERROR) {
if (ngx_event_flags & NGX_USE_EPOLL_EVENT) {
ngx_del_conn(c, 0);
}
ngx_close_connection(c);
return;
}
if ((ngx_event_flags & NGX_USE_EVENTPORT_EVENT) &&
(ngx_add_event(ev, NGX_READ_EVENT, 0) == NGX_ERROR)) {
return;
}
if (n == NGX_AGAIN) { return; }

//the custom command now.
if(ch.command==NGX_CMD_HTTP_PUSH_CHECK_MESSAGES) {
//take a look at the message queue for this worker process
in shared memory.
}
}
}

/* elsewhere, in a different worker process: */
if(/*some condition*/) {
ngx_channel_t ch;
ch.command = NGX_CMD_HTTP_PUSH_CHECK_MESSAGES;
ch.fd = -1;

if((ngx_write_channel(ngx_processes[request_owner_worker_process_slot].channel[0
/*or 1?*/], &ch, sizeof(*ch), some_log))!=NGX_OK) {
//do some error handling
}
}


Thanks again,
- Leo