gh-106078: Move static objects related to CONTEXTVAR to the decimal module global state

[CharlieZhao95]

Move following objects related to the CONTEXTVAR to decimal module global state.

• tls_context_key
• cached_context
• current_context_var

• Issue: Isolate the _decimal extension module #106078

[CharlieZhao95]

I executed the build and unit tests locally as follows. The result looks good.

# build
./configure --without-decimal-contextvar
make

# unittest
./python -m test test_decimal

cd ./Modules/_decimal/tests
./runall-memorydebugger.sh

BTW, do we have a CI pipeline that tests build with different compile options, such as --without-decimal-contextvar here. It seems that the current CI pipeline cannot detect build errors in the #ifndef WITH_DECIMAL_CONTEXTVAR block.

[CharlieZhao95]

cc: @kumaraditya303 @erlend-aasland

[erlend-aasland]

Instead of moving the entire struct, you can use forward declarations for the needed types.

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[CharlieZhao95]

Instead of moving the entire struct, you can use forward declarations for the needed types.

 This is an alias for an anonymous struct. We cannot forward declare anonymous structs or typedefs :(

A solution is to name these structs. For example:

struct PyDecContextObject;

typedef struct {
    ...
    struct PyDecContextObject *cached_context;
    ...
} decimal_state;

typedef struct PyDecContextObject {
    PyObject_HEAD
    mpd_context_t ctx;
    PyObject *traps;
    PyObject *flags;
    int capitals;
    PyThreadState *tstate;
} PyDecContextObject;

There is no harm and now you can forward declare it.

[erlend-aasland]

It's no hinder that the structs are anonymous. C has solutions for that as well. Let me know if you need a hint.

Alternatively, add a name to them. There is no harm in that, and it is quite normal throughout the code base.

Examples:

• Modules/cjkcodecs/multibytecodec.h
• Include/pytypedefs.h

[CharlieZhao95]

It's no hinder that the structs are anonymous. C has solutions for that as well. Let me know if you need a hint.

I don't know if your solution is to move the typedef struct {...} struct_name; to the top of the .c file or into the .h file. If not, please let me know!

Alternatively, add a name to them. There is no harm in that, and it is quite normal throughout the code base.

Thanks! I prefer to add names to these structures :)

[erlend-aasland]

Tested locally with ./configure --without-decimal-contextvar. LGTM.