Send task's functions separately with send_object()

[rafa-be]

Client.send_object() allows constant arguments to be sent only once when calling Client.submit() multiple time.

It would be nice to also allow functions to be serialized and send once using the same mechanism:

func_ref = client.send_object(my_function)

fut_1 = client.submit(func_ref, arg_1)
fut_2 = client.submit(func_ref, arg_2)

[rafa-be]

I had some time to experiment with this. Sadly, the gain is way less than I expected (0.05 to 0.1 ms per call to submit()).

That's because the client is already caching the function, thanks to how the function ID is generated (using an MD5 hash).

Thus the only benefit is that the function is only serialized once. But Cloudpickle's function serialization is pretty fast.

>>> c = Client("tcp://127.0.0.1:1234")

>>> sqrt_ref = c.send_object(math.sqrt)

>>> %timeit fut = c.submit(math.sqrt, 16)
74.3 μs ± 325 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)

>>> %timeit fut = c.submit(sqrt_ref, 16)
39.4 μs ± 210 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)

>>> %timeit c.submit(math.sqrt, 16).result()
1.98 ms ± 39.2 μs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)

>>> %timeit c.submit(sqrt_ref, 16).result()
1.87 ms ± 41.6 μs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)

I'd not say that the gain is negligible, but I'm not sure it makes sense considering it adds some (limited) complexity to the client's code.

See rafa-be/scaler@df430e6 for the implementation.