Multiprocessing in tensor computations does not work under macOS

[egourgoulhon]

Multiprocessing, as implemented in differential geometry computations via

sage: Parallelism().set(nproc=8)

does not work under macOS. This has been reported by many users, a recent report being ​https://groups.google.com/d/msg/sage-support/0RsGgb3lmZg/zNTMFLH9AQAJ

Note there is no issue within the doctest framework, i.e. the doctests involving parallel computations implemented in src/sage/manifolds/differentiable and src/sage/tensor/modules are passed on macOS machines.

[dimpase]

it is not clear how to see that it is broken. Could you point at a doctest that doesn't work at the Sage prompt?

[egourgoulhon]

Replying to dimpase:

it is not clear how to see that it is broken. Could you point at a doctest that doesn't work at the Sage prompt?

For instance, the doctest about the ​parallelization of the Lie derivative, a short version of which is

sage: M = Manifold(2, 'M')
sage: X.<x,y> = M.chart()
sage: v = M.vector_field(-y, x)
sage: w = M.one_form(y^2*sin(x), x^3*cos(y))
sage: Parallelism().set(nproc=2)
sage: w.lie_derivative(v).display()
(-y^3*cos(x) + x^3*cos(y) + 2*x*y*sin(x)) dx 
 + (-x^4*sin(y) - 3*x^2*y*cos(y) - y^2*sin(x)) dy

[egourgoulhon]

The OP at ​https://groups.google.com/d/msg/sage-support/0RsGgb3lmZg/WNxT_rzNAwAJ says that the problem is fixed in Sage 9.1. Dima, can you confirm this? (sorry I don't have any macOS computer at hand...). If yes, we may close this ticket.

[dimpase]

works for me on macOS and Sage 9.2.beta0

[egourgoulhon]

Replying to dimpase:

works for me on macOS and Sage 9.2.beta0

Thank you Dima!