bpo-1635741: port multiprocessing to multiphase init

[koubaa]

https://bugs.python.org/issue1635741

[vstinner]

Hum, right now, I still cannot build the extension module. Example of errors:

/home/vstinner/python/master/Modules/_multiprocessing/multiprocessing.c:192:5: error: expected ‘while’ before ‘if’
  192 |     if (PyDict_SetItemString(flags, #name, value) < 0) {    \
      |     ^~
/home/vstinner/python/master/Modules/_multiprocessing/multiprocessing.c:200:5: note: in expansion of macro ‘ADD_FLAG’
  200 |     ADD_FLAG(HAVE_SEM_OPEN);
      |     ^~~~~~~~
In file included from ./Include/pytime.h:6,
                 from ./Include/Python.h:85,
                 from /home/vstinner/python/master/Modules/_multiprocessing/multiprocessing.h:6,
                 from /home/vstinner/python/master/Modules/_multiprocessing/multiprocessing.c:10:
/home/vstinner/python/master/Modules/_multiprocessing/multiprocessing.c:196:15: error: ‘value’ undeclared (first use in this function)
  196 |     Py_DECREF(value)                                        \
      |               ^~~~~
./Include/object.h:112:41: note: in definition of macro ‘_PyObject_CAST’
  112 | #define _PyObject_CAST(op) ((PyObject*)(op))
      |                                         ^~

} in return -1; } of ADD_FLAG is too much and should be removed.

Also, there is a missing ";" at the end of the macro, after Py_DECREF(value).

Well, see my previous comment.

I'm not sure if you updated the PR or not in the meanwhile.

Try to build Python locally.

[koubaa]

@vstinner strange. It builds fine for me and the CI (on windows). I'll try to see why ubuntu/mac are not building.

[koubaa]

@vstinner now it makes sense. On windows all the uses of ADD_FLAG are disabled by the preprocessor. I manually defined HAVE_SEM_OPEN to 1 to figure out the macro issue.

[koubaa]

@vstinner can this be merged?

[shihai1991]

Oh, I have a comment but I forget press the submit button.

[vstinner]

@shihai1991 @corona10: Would you mind to review this PR? (use the Approve button if it LGTY).

[shihai1991]

Thanks, LGTM.

[vstinner]

Thanks @koubaa, merged. Thanks for reviews @shihai1991 and @corona10.