gh-106078: Suppress the warning caused by multi-phase initialization of decimal

[CharlieZhao95]

>>> python -m test test_decimal
Running Release|x64 interpreter...
0:00:00 Run tests sequentially
0:00:00 [1/1] test_decimal
...: warning: mpd_setminalloc: ignoring request to set MPD_MINALLOC a second time

This warnning is caused by the multi-phase initialization of decimal module. When decimal module is repeatedly imported, decimal_exec will be executed multiple times and this warning will be raised.

See #107287 (comment) for details.

• Issue: Isolate the _decimal extension module #106078

[CharlieZhao95]

Maybe we can skip news for this PR.

[CharlieZhao95]

It looks like the global variable check is failing, the tool cannot ignore static variables inside functions. Adding
__attribute__((constructor)) might be a more elegant option.
Forget this. Unfortunately, there is no equivalent for __attribute__((constructor)) on Windows.

[Eclips4]

I've tested it locally, and it works. Multiple imports of decimal doesn't make any warnings anymore.
LGTM.

[AlexWaygood]

The warning that's being suppressed here was recently brought up again in #110266

[erlend-aasland]

See also the discussion about a global init/exit API for extension modules.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x RHEL7 LTO + PGO 3.x has failed when building commit de10522.

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HEAD is now at de10522... gh-106078: Suppress the warning caused by multi-phase initialization of `decimal` (#107524)
Switched to and reset branch 'main'

find: ‘build’: No such file or directory
find: ‘build’: No such file or directory
find: ‘build’: No such file or directory
find: ‘build’: No such file or directory
make[2]: [clean-retain-profile] Error 1 (ignored)
Python/instrumentation.c: In function ‘allocate_instrumentation_data’:
Python/instrumentation.c:1497:9: warning: missing braces around initializer [-Wmissing-braces]
         code->_co_monitoring->local_monitors = (_Py_LocalMonitors){ 0 };
         ^
Python/instrumentation.c:1497:9: warning: (near initialization for ‘(anonymous).tools’) [-Wmissing-braces]
Python/instrumentation.c:1498:9: warning: missing braces around initializer [-Wmissing-braces]
         code->_co_monitoring->active_monitors = (_Py_LocalMonitors){ 0 };
         ^
Python/instrumentation.c:1498:9: warning: (near initialization for ‘(anonymous).tools’) [-Wmissing-braces]
Objects/bytes_methods.c: In function ‘find_internal’:
Objects/bytes_methods.c:526:31: warning: ‘subobj’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         if (PyObject_GetBuffer(subobj, &subbuf, PyBUF_SIMPLE) != 0)
                               ^
Objects/bytes_methods.c: In function ‘_Py_bytes_find’:
Objects/bytes_methods.c:526:31: warning: ‘subobj’ may be used uninitialized in this function [-Wmaybe-uninitialized]
Objects/bytes_methods.c:513:15: note: ‘subobj’ was declared here
     PyObject *subobj;
               ^
Objects/bytes_methods.c: In function ‘_Py_bytes_rfind’:
Objects/bytes_methods.c:526:31: warning: ‘subobj’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         if (PyObject_GetBuffer(subobj, &subbuf, PyBUF_SIMPLE) != 0)
                               ^
Objects/bytes_methods.c:513:15: note: ‘subobj’ was declared here
     PyObject *subobj;
               ^
Objects/bytes_methods.c: In function ‘_Py_bytes_count’:
Objects/bytes_methods.c:675:31: warning: ‘sub_obj’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         if (PyObject_GetBuffer(sub_obj, &vsub, PyBUF_SIMPLE) != 0)
                               ^
Python/instrumentation.c: In function ‘allocate_instrumentation_data’:
Python/instrumentation.c:1497:9: warning: missing braces around initializer [-Wmissing-braces]
         code->_co_monitoring->local_monitors = (_Py_LocalMonitors){ 0 };
         ^
Python/instrumentation.c:1497:9: warning: (near initialization for ‘(anonymous).tools’) [-Wmissing-braces]
Python/instrumentation.c:1498:9: warning: missing braces around initializer [-Wmissing-braces]
         code->_co_monitoring->active_monitors = (_Py_LocalMonitors){ 0 };
         ^
Python/instrumentation.c:1498:9: warning: (near initialization for ‘(anonymous).tools’) [-Wmissing-braces]
Python/pytime.c: In function ‘pytime_mul’:
Python/pytime.c:1388:1: note: correcting inconsistent profile data
 }
 ^
./Modules/_io/clinic/fileio.c.h: In function ‘_io_FileIO_close’:
./Modules/_io/fileio.c:175:32: warning: ‘exc’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         _PyErr_ChainExceptions1(exc);
                                ^
./Modules/_io/fileio.c:160:15: note: ‘exc’ was declared here
     PyObject *exc;
               ^
./Modules/_io/clinic/textio.c.h: In function ‘_io_TextIOWrapper_seek’:
./Modules/_io/textio.c:2601:45: warning: ‘MEM[(char * {ref-all})&cookie + 20B]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         decoded = PyObject_CallMethodObjArgs(self->decoder, &_Py_ID(decode),
                                             ^
./Modules/_io/textio.c:2452:17: note: ‘MEM[(char * {ref-all})&cookie + 20B]’ was declared here
     cookie_type cookie;
                 ^
./Modules/_io/textio.c:2610:54: warning: ‘MEM[(char * {ref-all})&cookie + 16B]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         if (PyUnicode_GetLength(self->decoded_chars) < cookie.chars_to_skip) {
                                                      ^
./Modules/_io/textio.c:2452:17: note: ‘MEM[(char * {ref-all})&cookie + 16B]’ was declared here
     cookie_type cookie;
                 ^
./Modules/_io/textio.c:2420:40: warning: ‘MEM[(char * {ref-all})&cookie + 8B]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     return _textiowrapper_encoder_reset(
                                        ^
./Modules/_io/textio.c:2452:17: note: ‘MEM[(char * {ref-all})&cookie + 8B]’ was declared here
     cookie_type cookie;
                 ^
./Modules/_io/textio.c:2420:40: warning: ‘MEM[(char * {ref-all})&cookie]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     return _textiowrapper_encoder_reset(
                                        ^
./Modules/_io/textio.c:2452:17: note: ‘MEM[(char * {ref-all})&cookie]’ was declared here
     cookie_type cookie;
                 ^

make: *** [buildbottest] Error 5