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2015-12-18MAINT-5976: Fix bug in LLCoros::set_consuming() mechanism.Nat Goodspeed
The original implementation of set_consuming() involved a bool* pointing to a local bool in VoidListener::operator()()'s stack frame. postAndSuspend() would set that bool (through the pointer) as soon as it returned from suspension. The trouble with that is that LLEventMailDrop potentially calls its new listener (fulfilling the future) immediately in the listen_impl() override -- in other words, way up at the top of postAndSuspend(), well before the code that sets the relevant bool. Instead, make the adapter formerly known as VoidListener bind the coroutine's get_consuming() value at adapter construction time (before listening on the LLEventPump), so that its operator()() has the coroutine's correct get_consuming() value to return. Eliminating the bool* makes the code both simpler AND more correct! This change makes that adapter very specific to coroutine usage. Rename it FutureListener and migrate it from lleventcoros.h into the .cpp file. Nobody else was using it anyway. Make corresponding changes to postAndSuspend2() and its WaitForEventOnHelper class -- whose name no longer corresponds to the function as it used to. Rename that one FutureListener2. The new FutureListener functionality, common to both these adapters, makes it useful to derive FutureListener2 from FutureListener. Introduce llmake(), a generic function to deduce template type arguments from function parameter types. This allows us to remove the voidlistener() and wfeoh() helper functions. Hiding VoidListener broke one of the lleventcoro_test.cpp tests. But that test was sort of a lame recap of an earlier implementation of postAndSuspend(), based on LLEventPump events. Recast that test to illustrate how to use a coroutine future to suspend a coroutine for something other than an LLEventPump. But that rubbed my nose in the fact that we MUST wrap future's context switching with proper management of the current coroutine. Introduce LLCoros::Future<T>, which wraps boost::dcoroutines::future<T>. Use LLCoros::Future<T> in postAndSuspend() and postAndSuspend2().