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Include/internal/pycore_runtime_init.h

cpython 3.14 @ ab2d84fe1023/Include/internal/pycore_runtime_init.h

Compile-time initialization macros for the CPython runtime state. This header defines the zero-initialized blobs that let CPython statically allocate _PyRuntimeState and the initial interpreter state before any C code runs.

Map​

LinesSymbolRole
1-80_PyRuntimeState_INITDesignated-initializer macro for the global _PyRuntime variable
80-150_Py_interp_config_INITDefault PyInterpreterConfig for the main interpreter
150-200INTERP_CREATED_DURING_RUNTIME_INITSentinel for partially-constructed interpreters

Reading​

_PyRuntimeState_INIT​

CPython needs a fully-formed _PyRuntimeState available from the very first instruction of the process, before Py_Initialize is called. Rather than calling malloc and memset, the runtime is declared as a static global and seeded with designated-initializer macros that the C compiler evaluates at link time.

// Include/internal/pycore_runtime_init.h (CPython 3.14)
#define _PyRuntimeState_INIT(runtime, open_code_hook) \
    { \
        .calls_to_do = 0, \
        .gilstate = _gilstate_INIT(runtime), \
        .interpreters = { \
            .mutex = _PyMutex_STATIC_INIT, \
            .next_id = -1, \
        }, \
        .ceval = { \
            .perf = _Py_PERF_PROFILING_INIT, \
        }, \
        .open_code_hook = open_code_hook, \
    }

The runtime argument is the address of the static _PyRuntime variable itself, used so that embedded pointers inside the struct can reference their own parent without a run-time fixup step.

_Py_interp_config_INIT​

A second macro provides the default PyInterpreterConfig for the main interpreter. It sets the GIL policy, memory allocator selection, and feature-flag fields that a user-visible PyConfig object is later merged on top of.

#define _Py_interp_config_INIT \
    { \
        .use_main_obmalloc = 1, \
        .allow_fork = 1, \
        .allow_exec = 1, \
        .allow_threads = 1, \
        .allow_daemon_threads = 1, \
        .check_multi_interp_extensions = 0, \
        .gil = PyInterpreterConfig_SHARED_GIL, \
    }

Sub-interpreters created after the main one inherit these defaults unless the caller overrides them via Py_NewInterpreterFromConfig.

INTERP_CREATED_DURING_RUNTIME_INIT sentinel​

The header also defines the sentinel INTERP_CREATED_DURING_RUNTIME_INIT. It is stored in interp->_initialized while _Py_InitializeMain is still running and is used to distinguish the partially-constructed main interpreter from fully-ready sub-interpreters. Any path that calls PyThreadState_Get before _Py_InitializeMain completes will see this sentinel and can bail out gracefully.

gopy notes​

Not yet ported. gopy's runtime initialization follows a different path: pythonrun.RunString bootstraps interpreter state procedurally rather than via static zero-initialization. The conceptual equivalent lives in pythonrun/runstring.go and vm/eval_gen.go.