[Python-checkins] gh-127945: add locking to malloc closure in free-threading (#131662)

[kumaraditya303]

https://github.com/python/cpython/commit/96ef4c511f3ec763dbb06a1f3c23c658a09403a1
commit: 96ef4c511f3ec763dbb06a1f3c23c658a09403a1
branch: main
author: Kumar Aditya <kumaradi...@python.org>
committer: kumaraditya303 <kumaradi...@python.org>
date: 2025-03-25T16:48:46+05:30
summary:

gh-127945: add locking to malloc closure in free-threading (#131662)

The freelist is not thread safe in free-threading so this adds lock around it 
make it thread safe in free-threading.

files:
M Modules/_ctypes/malloc_closure.c

diff --git a/Modules/_ctypes/malloc_closure.c b/Modules/_ctypes/malloc_closure.c
index bb4f8f21bd3f77..80ba96614bff79 100644
--- a/Modules/_ctypes/malloc_closure.c
+++ b/Modules/_ctypes/malloc_closure.c
@@ -27,6 +27,16 @@
 
 /******************************************************************/
 
+
+#ifdef Py_GIL_DISABLED
+static PyMutex malloc_closure_lock;
+# define MALLOC_CLOSURE_LOCK()   PyMutex_Lock(&malloc_closure_lock)
+# define MALLOC_CLOSURE_UNLOCK() PyMutex_Unlock(&malloc_closure_lock)
+#else
+# define MALLOC_CLOSURE_LOCK()   ((void)0)
+# define MALLOC_CLOSURE_UNLOCK() ((void)0)
+#endif
+
 typedef union _tagITEM {
     ffi_closure closure;
     union _tagITEM *next;
@@ -110,9 +120,11 @@ void Py_ffi_closure_free(void *p)
     }
 #endif
 #endif
+    MALLOC_CLOSURE_LOCK();
     ITEM *item = (ITEM *)p;
     item->next = free_list;
     free_list = item;
+    MALLOC_CLOSURE_UNLOCK();
 }
 
 /* return one item from the free list, allocating more if needed */
@@ -131,11 +143,15 @@ void *Py_ffi_closure_alloc(size_t size, void** codeloc)
     }
 #endif
 #endif
+    MALLOC_CLOSURE_LOCK();
     ITEM *item;
-    if (!free_list)
+    if (!free_list) {
         more_core();
-    if (!free_list)
+    }
+    if (!free_list) {
+        MALLOC_CLOSURE_UNLOCK();
         return NULL;
+    }
     item = free_list;
     free_list = item->next;
 #ifdef _M_ARM
@@ -144,5 +160,6 @@ void *Py_ffi_closure_alloc(size_t size, void** codeloc)
 #else
     *codeloc = (void *)item;
 #endif
+    MALLOC_CLOSURE_UNLOCK();
     return (void *)item;
 }

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