Statically initialize PyInterpreterState.gc.generations.

Author: ericsnowcurrently

Include/internal/pycore_gc.h

@@ -134,6 +134,7 @@ struct _gc_runtime_state {
     /* Current call-stack depth of tp_dealloc calls. */
     int trash_delete_nesting;
 
+    /* Is automatic collection enabled? */
     int enabled;
     int debug;
     /* linked lists of container objects */
@@ -161,6 +162,7 @@ struct _gc_runtime_state {
     Py_ssize_t long_lived_pending;
 };
 
+
 extern void _PyGC_InitState(struct _gc_runtime_state *);
 
 extern Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate);

Include/internal/pycore_runtime_init.h

@@ -40,7 +40,13 @@ extern "C" {
             .recursion_limit = Py_DEFAULT_RECURSION_LIMIT, \
         }, \
         .gc = { \
-            .enabled = 1,  /* automatic collection enabled? */ \
+            .enabled = 1, \
+            .generations = { \
+                /* .head is set in _PyGC_InitState(). */ \
+                { .threshold = 700, }, \
+                { .threshold = 10, }, \
+                { .threshold = 10, }, \
+            }, \
         }, \
         ._initial_thread = _PyThreadState_INIT, \
     }

Modules/gcmodule.c

@@ -139,22 +139,20 @@ get_gc_state(void)
 void
 _PyGC_InitState(GCState *gcstate)
 {
-#define _GEN_HEAD(n) GEN_HEAD(gcstate, n)
-    struct gc_generation generations[NUM_GENERATIONS] = {
-        /* PyGC_Head,                                    threshold,    count */
-        {{(uintptr_t)_GEN_HEAD(0), (uintptr_t)_GEN_HEAD(0)},   700,        0},
-        {{(uintptr_t)_GEN_HEAD(1), (uintptr_t)_GEN_HEAD(1)},   10,         0},
-        {{(uintptr_t)_GEN_HEAD(2), (uintptr_t)_GEN_HEAD(2)},   10,         0},
-    };
+#define INIT_HEAD(GEN) \
+    do { \
+        GEN.head._gc_next = (uintptr_t)&GEN.head; \
+        GEN.head._gc_prev = (uintptr_t)&GEN.head; \
+    } while (0)
+
     for (int i = 0; i < NUM_GENERATIONS; i++) {
-        gcstate->generations[i] = generations[i];
+        assert(gcstate->generations[i].count == 0);
+        INIT_HEAD(gcstate->generations[i]);
     };
     gcstate->generation0 = GEN_HEAD(gcstate, 0);
-    struct gc_generation permanent_generation = {
-          {(uintptr_t)&gcstate->permanent_generation.head,
-           (uintptr_t)&gcstate->permanent_generation.head}, 0, 0
-    };
-    gcstate->permanent_generation = permanent_generation;
+    INIT_HEAD(gcstate->permanent_generation);
+
+#undef INIT_HEAD
 }