gh-118527: Intern code consts in free-threaded build (#118667)

We already intern and immortalize most string constants. In the
free-threaded build, other constants can be a source of reference count
contention because they are shared by all threads running the same code
objects.

Include/internal/pycore_code.h

@@ -8,6 +8,8 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
+#include "pycore_lock.h"        // PyMutex
+
 
 // We hide some of the newer PyCodeObject fields behind macros.
 // This helps with backporting certain changes to 3.12.
@@ -16,6 +18,14 @@ extern "C" {
 #define _PyCode_HAS_INSTRUMENTATION(CODE) \
     (CODE->_co_instrumentation_version > 0)
 
+struct _py_code_state {
+    PyMutex mutex;
+    // Interned constants from code objects. Used by the free-threaded build.
+    struct _Py_hashtable_t *constants;
+};
+
+extern PyStatus _PyCode_Init(PyInterpreterState *interp);
+extern void _PyCode_Fini(PyInterpreterState *interp);
 
 #define CODE_MAX_WATCHERS 8
 

Include/internal/pycore_interp.h

@@ -245,6 +245,7 @@ struct _is {
     struct _Py_long_state long_state;
     struct _dtoa_state dtoa;
     struct _py_func_state func_state;
+    struct _py_code_state code_state;
 
     struct _Py_dict_state dict_state;
     struct _Py_exc_state exc_state;

Include/internal/pycore_setobject.h

@@ -30,6 +30,9 @@ PyAPI_DATA(PyObject *) _PySet_Dummy;
 
 PyAPI_FUNC(int) _PySet_Contains(PySetObject *so, PyObject *key);
 
+// Clears the set without acquiring locks. Used by _PyCode_Fini.
+extern void _PySet_ClearInternal(PySetObject *so);
+
 #ifdef __cplusplus
 }
 #endif