bpo-36301: Add _PyRuntime.pre_initialized (GH-12457)

* Add _PyRuntime.pre_initialized: set to 1 when Python
  is pre-initialized
* Add _Py_PreInitialize() and _Py_PreInitializeFromPreConfig().
* _PyCoreConfig_Read() now calls  _Py_PreInitialize().
* Move _PyPreConfig_GetGlobalConfig() and
  _PyCoreConfig_GetGlobalConfig() calls from main.c to preconfig.c
  and coreconfig.c.

Include/cpython/pylifecycle.h

@@ -14,6 +14,10 @@ PyAPI_FUNC(int) Py_SetStandardStreamEncoding(const char *encoding,
 
 /* PEP 432 Multi-phase initialization API (Private while provisional!) */
 
+PyAPI_FUNC(_PyInitError) _Py_PreInitialize(void);
+PyAPI_FUNC(_PyInitError) _Py_PreInitializeFromPreConfig(
+    _PyPreConfig *preconfig);
+
 PyAPI_FUNC(_PyInitError) _Py_InitializeCore(
     PyInterpreterState **interp,
     const _PyCoreConfig *);

Include/internal/pycore_pystate.h

@@ -134,8 +134,15 @@ struct _gilstate_runtime_state {
 /* Full Python runtime state */
 
 typedef struct pyruntimestate {
-    int initialized;
+    /* Is Python pre-initialized? Set to 1 by _Py_PreInitialize() */
+    int pre_initialized;
+
+    /* Is Python core initialized? Set to 1 by _Py_InitializeCore() */
     int core_initialized;
+
+    /* Is Python fully initialized? Set to 1 by Py_Initialize() */
+    int initialized;
+
     PyThreadState *finalizing;
 
     struct pyinterpreters {
@@ -172,7 +179,8 @@ typedef struct pyruntimestate {
     // XXX Consolidate globals found via the check-c-globals script.
 } _PyRuntimeState;
 
-#define _PyRuntimeState_INIT {.initialized = 0, .core_initialized = 0}
+#define _PyRuntimeState_INIT \
+    {.pre_initialized = 0, .core_initialized = 0, .initialized = 0}
 /* Note: _PyRuntimeState_INIT sets other fields to 0/NULL */
 
 PyAPI_DATA(_PyRuntimeState) _PyRuntime;

Modules/main.c

@@ -283,32 +283,30 @@ _PyMainInterpreterConfig_Read(_PyMainInterpreterConfig *main_config,
 /* --- pymain_init() ---------------------------------------------- */
 
 static _PyInitError
-preconfig_read_write(_PyPreConfig *config, const _PyArgv *args)
+pymain_init_preconfig(_PyPreConfig *config, const _PyArgv *args)
 {
-    _PyPreConfig_GetGlobalConfig(config);
-
     _PyInitError err = _PyPreConfig_ReadFromArgv(config, args);
     if (_Py_INIT_FAILED(err)) {
         return err;
     }
 
-    return _PyPreConfig_Write(config);
+    return _Py_PreInitializeFromPreConfig(config);
 }
 
 
 static _PyInitError
-config_read_write(_PyCoreConfig *config, const _PyArgv *args,
-                  const _PyPreConfig *preconfig)
+pymain_init_coreconfig(_PyCoreConfig *config, const _PyArgv *args,
+                       const _PyPreConfig *preconfig,
+                       PyInterpreterState **interp_p)
 {
-    _PyCoreConfig_GetGlobalConfig(config);
-
     _PyInitError err = _PyCoreConfig_ReadFromArgv(config, args, preconfig);
     if (_Py_INIT_FAILED(err)) {
         return err;
     }
 
     _PyCoreConfig_Write(config);
-    return _Py_INIT_OK();
+
+    return _Py_InitializeCore(interp_p, config);
 }
 
 
@@ -356,24 +354,17 @@ pymain_init(const _PyArgv *args, PyInterpreterState **interp_p)
     _PyCoreConfig local_config = _PyCoreConfig_INIT;
     _PyCoreConfig *config = &local_config;
 
-    err = preconfig_read_write(preconfig, args);
+    err = pymain_init_preconfig(preconfig, args);
     if (_Py_INIT_FAILED(err)) {
         goto done;
     }
 
-    err = config_read_write(config, args, preconfig);
-    if (_Py_INIT_FAILED(err)) {
-        goto done;
-    }
-
-    PyInterpreterState *interp;
-    err = _Py_InitializeCore(&interp, config);
+    err = pymain_init_coreconfig(config, args, preconfig, interp_p);
     if (_Py_INIT_FAILED(err)) {
         goto done;
     }
-    *interp_p = interp;
 
-    err = pymain_init_python_main(interp);
+    err = pymain_init_python_main(*interp_p);
     if (_Py_INIT_FAILED(err)) {
         goto done;
     }

Python/coreconfig.c

@@ -1367,6 +1367,11 @@ _PyCoreConfig_Read(_PyCoreConfig *config, const _PyPreConfig *preconfig)
 {
     _PyInitError err;
 
+    err = _Py_PreInitialize();
+    if (_Py_INIT_FAILED(err)) {
+        return err;
+    }
+
     _PyCoreConfig_GetGlobalConfig(config);
 
     if (preconfig != NULL) {
@@ -2025,6 +2030,8 @@ config_from_cmdline(_PyCoreConfig *config, _PyCmdline *cmdline,
     int need_usage = 0;
     _PyInitError err;
 
+    _PyCoreConfig_GetGlobalConfig(config);
+
     err = config_init_program(config, cmdline);
     if (_Py_INIT_FAILED(err)) {
         return err;

Python/preconfig.c

@@ -672,6 +672,8 @@ _PyPreConfig_ReadFromArgv(_PyPreConfig *config, const _PyArgv *args)
         goto done;
     }
 
+    _PyPreConfig_GetGlobalConfig(config);
+
     if (_PyPreConfig_Copy(&save_config, config) < 0) {
         err = _Py_INIT_NO_MEMORY();
         goto done;

Python/pylifecycle.c

@@ -714,19 +714,57 @@ _Py_InitializeCore_impl(PyInterpreterState **interp_p,
 }
 
 
+_PyInitError
+_Py_PreInitializeFromPreConfig(_PyPreConfig *config)
+{
+    if (config != NULL) {
+        _PyInitError err = _PyPreConfig_Write(config);
+        if (_Py_INIT_FAILED(err)) {
+            return err;
+        }
+    }
+
+    _PyRuntime.pre_initialized = 1;
+    return _Py_INIT_OK();
+}
+
+
 static _PyInitError
-pyinit_preconfig(_PyPreConfig *preconfig, const _PyPreConfig *src_preconfig)
+pyinit_preconfig(_PyPreConfig *config, const _PyPreConfig *src_config)
 {
-    if (_PyPreConfig_Copy(preconfig, src_preconfig) < 0) {
+    _PyInitError err;
+
+    err = _PyRuntime_Initialize();
+    if (_Py_INIT_FAILED(err)) {
+        return err;
+    }
+
+    if (_PyPreConfig_Copy(config, src_config) < 0) {
         return _Py_INIT_ERR("failed to copy pre config");
     }
 
-    _PyInitError err = _PyPreConfig_Read(preconfig);
+    err = _PyPreConfig_Read(config);
     if (_Py_INIT_FAILED(err)) {
         return err;
     }
 
-    return _PyPreConfig_Write(preconfig);
+    return _Py_PreInitializeFromPreConfig(config);
+}
+
+
+_PyInitError
+_Py_PreInitialize(void)
+{
+    _PyInitError err = _PyRuntime_Initialize();
+    if (_Py_INIT_FAILED(err)) {
+        return err;
+    }
+
+    if (_PyRuntime.pre_initialized) {
+        return _Py_INIT_OK();
+    }
+
+    return _Py_PreInitializeFromPreConfig(NULL);
 }