bpo-1635741: Convert socket.SocketType to heap type, and establish global state

[erlend-aasland]

Prepare the socket module for multi-phase init by converting socket.SocketType
to heap type, establish a global module state, and clean up the first part of the
init function.

https://bugs.python.org/issue1635741

[erlend-aasland]

@vstinner Do I need to create SocketType as a GC type with traverse function in this case? I can't find ref leaks with python.exe -m test -R 3:5 test_socket.

[erlend-aasland]

@shihai1991 / @corona10: In commit b41d9aa (clean up first part of init function), I assume the following:
When an object is successfully added to a module using PyModule_AddObjectRef, it is added to the module dict, which means that the module dict has a strong reference to the object, right? This also means that when the module is destroyed, the module dict, together with it's values, are also destroyed, right? Unless I'm missing something, I think this commit is ref leak safe :)

[shihai1991]

When an object is successfully added to a module using PyModule_AddObjectRef, it is added to the module dict, which means that the module dict has a strong reference to the object, right?

You are right :).

This also means that when the module is destroyed, the module dict, together with it's values, are also destroyed, right? Unless I'm missing something, I think this commit is ref leak safe :)

You are right, the object's dealloc() will be triaggered when the object's ref is zero. But the extension module's state can be take cared by the GC(it means that you don't need to free them manually). You can take a look m_traverse, m_free and m_clear in https://docs.python.org/3.10/c-api/module.html?highlight=m_traverse#c.PyModuleDef.m_traverse.

[erlend-aasland]

When an object is successfully added to a module using PyModule_AddObjectRef, it is added to the module dict, which means that the module dict has a strong reference to the object, right?
You are right :).

So, that means I only need to employ a strong ref to protect the object while calling PyModule_AddObjectRef: In the ADD_OBJ_REF macro, wrap PyModule_AddObjectRef with Py_INCREF and Py_DECREF. Right?

Thank you ! :)

[erlend-aasland]

AFAICS, @shihai1991, there are ref three scenarios for extension modules:

1. C API: Make sure the module keeps strong refs to the capsule object for the lifetime of the capsule.
2. Module state: Make sure the module keeps strong refs to the state objects for the lifetime of the state.
3. Module dict: Make sure the module keeps strong refs to the objects only until the module dict has acquired its own strong refs.

Did I miss anything?

[shihai1991]

AFAICS, @shihai1991, there are ref three scenarios for extension modules:

1. C API: Make sure the module keeps strong refs to the capsule object for the lifetime of the capsule.
2. Module state: Make sure the module keeps strong refs to the state objects for the lifetime of the state.
3. Module dict: Make sure the module keeps strong refs to the objects only until the module dict has acquired its own strong refs.

Did I miss anything?

No, I have no other info to supply :)

[github-actions]

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