[PATCH] tevent and threads - infrastructure improvements.

[Stefan (metze) Metzmacher]

Hi Jeremy,

> The reason was that libev has the function:
> 
> ev_async_send()
> 
> which allows one thread to schedule a callback
> on the event loop of another thread.
> 
> I knew this could be done in tevent, but didn't
> have an elegant (a matter of opinion of course :-)
> solution, so I coded one up. Here it is for your
> review.
> 
> It has the advantage that if you don't need
> the functionality to schedule a callback
> on the event loop of another thread, you don't
> pay any costs in regular tevent usage.
> 
> It adds 3 functions to tevent:
> 
> int tevent_threaded_context_register(struct tevent_context *ev);
> 
> which sets up the background data structures
> needed for the functionality.
> 
> int tevent_threaded_context_unregister(struct tevent_context *ev);
> 
> which tears them down again, and finally:
> 
> int tevent_threaded_async_call(struct tevent_context *dest_ev_ctx,
>                                 void (*callback_fn)(struct tevent_context *,
>                                                 void *),
>                                 void **pp_private);

void ** is not valid in an argument list.

> which asynchronously schedules callback_fn to be invoked
> on the destination context under the thread that's running
> it's event loop.

This somehow feels unnatural in the tevent environment.

Something like this would be better:

struct tevent_context *tevent_thread_proxy_context(struct tevent_context
*main_ev);

The thread can then only schedule immediate events on the returned proxy
context, this will wakeup the main_ev and move the immediate events from
the proxy to the main_ev.

The immediate events can be preallocated in before starting the thread.

metze

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