yield() should not allocate

[PatrickHaecker]

julia> @allocated yield()
64

In an ideal world, yield() should not allocate. I am not sure whether this is possible in general. But my gut feeling is that it should at least be possible when yield() is effectively a no-op as the same task continues.

Maybe being able to preallocate the workqueue so that it does not allocate in practice could be an option?