bpo-38070: Add _PyRuntimeState.preinitializing (GH-16245)

Add _PyRuntimeState.preinitializing field: set to 1 while
Py_PreInitialize() is running.

_PyRuntimeState: rename also pre_initialized field to preinitialized.

Include/internal/pycore_pystate.h

@@ -190,8 +190,11 @@ struct _gilstate_runtime_state {
 /* Full Python runtime state */
 
 typedef struct pyruntimestate {
-    /* Is Python pre-initialized? Set to 1 by Py_PreInitialize() */
-    int pre_initialized;
+    /* Is running Py_PreInitialize()? */
+    int preinitializing;
+
+    /* Is Python preinitialized? Set to 1 by Py_PreInitialize() */
+    int preinitialized;
 
     /* Is Python core initialized? Set to 1 by _Py_InitializeCore() */
     int core_initialized;
@@ -199,6 +202,8 @@ typedef struct pyruntimestate {
     /* Is Python fully initialized? Set to 1 by Py_Initialize() */
     int initialized;
 
+    /* Set by Py_FinalizeEx(). Only reset to NULL if Py_Initialize()
+       is called again. */
     PyThreadState *finalizing;
 
     struct pyinterpreters {
@@ -241,7 +246,7 @@ typedef struct pyruntimestate {
 } _PyRuntimeState;
 
 #define _PyRuntimeState_INIT \
-    {.pre_initialized = 0, .core_initialized = 0, .initialized = 0}
+    {.preinitialized = 0, .core_initialized = 0, .initialized = 0}
 /* Note: _PyRuntimeState_INIT sets other fields to 0/NULL */
 
 PyAPI_DATA(_PyRuntimeState) _PyRuntime;

Python/pylifecycle.c

@@ -725,11 +725,15 @@ _Py_PreInitializeFromPyArgv(const PyPreConfig *src_config, const _PyArgv *args)
     }
     _PyRuntimeState *runtime = &_PyRuntime;
 
-    if (runtime->pre_initialized) {
+    if (runtime->preinitialized) {
         /* If it's already configured: ignored the new configuration */
         return _PyStatus_OK();
     }
 
+    /* Note: preinitialized remains 1 on error, it is only set to 0
+       at exit on success. */
+    runtime->preinitializing = 1;
+
     PyPreConfig config;
     _PyPreConfig_InitFromPreConfig(&config, src_config);
 
@@ -743,7 +747,8 @@ _Py_PreInitializeFromPyArgv(const PyPreConfig *src_config, const _PyArgv *args)
         return status;
     }
 
-    runtime->pre_initialized = 1;
+    runtime->preinitializing = 0;
+    runtime->preinitialized = 1;
     return _PyStatus_OK();
 }
 
@@ -783,7 +788,7 @@ _Py_PreInitializeFromConfig(const PyConfig *config,
     }
     _PyRuntimeState *runtime = &_PyRuntime;
 
-    if (runtime->pre_initialized) {
+    if (runtime->preinitialized) {
         /* Already initialized: do nothing */
         return _PyStatus_OK();
     }