Fix invalid function cast warnings with gcc 8
for method conventions different from METH_NOARGS, METH_O and
METH_VARARGS excluding Argument Clinic generated code.
All the subinterpreter tests were disabled in gh-7513. This commit re-enables them, but leaves one bad test disabled. The test is partly causing problems because it makes assumptions about the availability of a high-level interpreters module (see PEP 554). So I'm disabling the test until such a high-level module is available.
For bpo-32604 I added extra subinterpreter-related tests (see #6914), which caused a few buildbots to crash. This patch fixes the crash by ensuring that refcounts in channels are handled properly.
METH_NOARGS functions need only a single argument but they are cast
into a PyCFunction, which takes two arguments. This triggers an
invalid function cast warning in gcc8 due to the argument mismatch.
Fix this by adding a dummy unused argument.
The CPython runtime assumes that there is a one-to-one relationship (for a given interpreter) between PyThreadState and OS threads. Sending and receiving on a channel in the same interpreter was causing crashes because of this (specifically due to a check in PyThreadState_Swap()). The solution is to not switch threads if the interpreter is the same.
Serhiy Storchaka
Victor Stinner
Peter Eisentraut
Alexey Izbyshev
Benjamin Peterson
Eric Snow
Siddhesh Poyarekar