Re: [Libevent-users] HTTP and thread safety

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Mon, Jan 31, 2011 at 12:42 PM, Marco <marco.tijuana@xxxxxxxxx> wrote:
> Hi everyone, simple question..
>
> 2 threads, T1 is in the event loop, T2 does some other things.
> Assume that I have a safe way of communicating between T1 and T2.
>
> I'm planning to use T2 to create http requests objects and then give them to
> T1 to actually perform the request, i.e.:
>
> T2 calls
> - evhttp_connection_base_new
> - evhttp_connection_set_timeout
> - evhttp_connection_set_retries
> - evhttp_connection_set_closecb
> - evhttp_request_new
>
> Then T2 passes the evhttp_connection and evhttp_request to T1, who calls
> evhttp_make_request.
> (again, assume this message passing is implemeted safely)
>
> Is this thread safe?
> Or does any of the functions invoked by T2 modify the event base (owned by
> T1)?

Hm.  All I can go with in response here is that "evhttp is not
threadsafe"; nobody has done the sufficient thread-safety analysis on
it.  From what I can see, evhttp_connection_base_new makes a
non-threadsafe bufferevent, which will indeed add and remove events
from the event base.  bufferevent_set_timeout, called by
evhttp_conection_set_timeout, also manipulates events.

I think you *might* be okay here, but I really can't guarantee it
unless somebody takes a good hard look at the evhttp code in question.

-- 
Nick
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