gh-100227: Lock Around Modification of the Global Allocators State (gh-105516)

The risk of a race with this state is relatively low, but we play it safe anyway. We do avoid using the lock in performance-sensitive cases where the risk of a race is very, very low.

Author: ericsnowcurrently

Include/internal/pycore_pymem.h

@@ -18,6 +18,7 @@ typedef struct {
 } debug_alloc_api_t;
 
 struct _pymem_allocators {
+    PyThread_type_lock mutex;
     struct {
         PyMemAllocatorEx raw;
         PyMemAllocatorEx mem;

Include/internal/pycore_runtime_init.h

@@ -25,9 +25,9 @@ extern PyTypeObject _PyExc_MemoryError;
 #define _PyRuntimeState_INIT(runtime) \
     { \
         .allocators = { \
-            _pymem_allocators_standard_INIT(runtime), \
-            _pymem_allocators_debug_INIT, \
-            _pymem_allocators_obj_arena_INIT, \
+            .standard = _pymem_allocators_standard_INIT(runtime), \
+            .debug = _pymem_allocators_debug_INIT, \
+            .obj_arena = _pymem_allocators_obj_arena_INIT, \
         }, \
         .obmalloc = _obmalloc_global_state_INIT, \
         .pyhash_state = pyhash_state_INIT, \