`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?

[nsajko]

Can't reproduce, what's the versioninfo()?

[nsajko]

An off the cuff workaround idea: the return type of yield() sadly infers as Any, so maybe something like this would help:

function yield_workaround()
    yield()
    nothing
end
@allocated yield_workaround()

[nsajko]

Also, if you can still reproduce, a flame graph from the allocation profiler might be nice.

[oscardssmith]

is this just another case of @allocated being broken in 1.12?

[gbaraldi]

yield will by definition exercise the julia scheduler which may allocate depending on it's implementation (it might even be optimal). So this isn't really actionable

[PatrickHaecker]

Julia 1.11.5:

julia> @allocated yield()
64

Julia 1.12.0-beta1:

julia> @allocated yield()
0

Julia 1.13.0-DEV.393 (2025-04-14):

julia> @allocated yield()
0

So, indeed, there is nothing more to do with a single task (and this is what this issue is about). Thanks to everyone involved and sorry for not testing this with more recent versions.

[PatrickHaecker]

An off the cuff workaround idea: the return type of yield() sadly infers as Any, so maybe something like this would help:

function yield_workaround()
yield()
nothing
end
@allocated yield_workaround()

Thanks for the idea. Just for documenting it: This did not solve the issue for 1.12. However, I am happy that 1.12 seems to fix the issue.