On Sun, Jun 20, 2010 at 5:51 AM, Avi Bab <a...@breach.com> wrote: > Hello all, > > > > I’d like to use a socket based bufferevent to perform asynchronous writing > to the underlying socket: > > One thread, X, adds data to the output evbuffer (either by > evbuffer_reserve_space+ evbuffer_commit_space or by evbuffer_add_reference) > and another thread, Y, dispatches on the bufferevent’s event_base (i.e., > actually sends the data via the socket). > > My questions are – > > Does thread X need to perform locking on the evbuffer? > > If so then how can I have thread Y synchronize on the same locks? > > I assume that setting the bufferevent option BEV_OPT_THREADSAFE will not > affect the “direct” access to the evbuffer by X.
Setting BEV_OPT_THREADSAFE will make the evbuffers and the bufferevents all get locks, which should work fine for most operations. As of Libevent 2.0, a bufferevent and the two evbuffers associated with it all share the same lock. (Some future version might get smarter here; but in practice the current approach seems good enough.) There's one wrinkle here, though: sometimes you want a *set* of operations on a bufferevent or evbuffer to be atomic. For example, even though evbuffer_reserve_space() is locked, and evbuffer_commit_space() is locked, you still don't want another thread modifying an evbuffer in between when you call evbuffer_reserve_space() and evbuffer_commit_space(). You can prevent this by calling evbuffer_lock() before you start doing the operations you want to be atomic, and evbuffer_unlock() when the atomic operations are finished. Libevent 2.0.6-rc will introduce a bufferevent_lock()/bufferevent_unlock() pair to perform the same function on bufferevents. yrs, -- Nick *********************************************************************** To unsubscribe, send an e-mail to majord...@freehaven.net with unsubscribe libevent-users in the body.
