kc3-lang/libevent

2010-01-14T16:30:40

Changelist code to defer event changes until just before dispatch This is necessary or useful for a few reasons: 1) Sometimes applications will add and delete the same event more than once between calls to dispatch. Processing these changes immediately is needless, and potentially expensive (especially if we're on a system that makes one syscall per changed event). Yes, this actually happens in practice for nonpathological code, such as in cases where the user's callback conditionally re-adds a non-persistent event, or where draining a buffer turns off writing and invokes a user callback which adds more data which in turn re-enabled writing. 2) Sometimes we can coalesce multiple changes on the same fd into a single syscall if we know about them in advance. For example, epoll can do an add and a delete at the same time, but only if we have found out about both of them before we tell epoll. 3) Sometimes adding an event that we immediately delete can cause unintended consequences: in kqueue, this makes pending events get reported spuriously.