Summary:
Allocations are expensive, especially when done under a lock as this increase
the critical section, reducing the potential concurrency. While this yields to
a 1.25x speedup, this is more of a sideway improvement as the allocation is now
done prior to enqueuing. This also means that de-duplicating requests is now
more expensive, as no allocation would be done before, but at the same time,
de-duplication is the non-common code path, so the tradeoff is worthwhile.
Reviewed By: chadaustin
Differential Revision: D30520228
fbshipit-source-id: 99dea65e828f9c896fdfca6b308106554c989282
f3dc469957