Use st_table with num hash for gcguard table

PTR2NUM may allocate a new object. This makes the process abort by object
allocation during GC.  Using st_table instead of a Hash can avoid this
problem.

Author: mrkn

ext/pycall/gc.c

@@ -1,5 +1,71 @@
 #include "pycall_internal.h"
 
+struct gcguard {
+  st_table *guarded_objects;
+};
+
+static int
+gcguard_mark_i(st_data_t key, st_data_t val, st_data_t arg)
+{
+  VALUE obj = (VALUE)val;
+  rb_gc_mark(obj);
+  return ST_CONTINUE;
+}
+
+static void
+gcguard_mark(void* ptr)
+{
+  struct gcguard *gg = (struct gcguard *)ptr;
+  st_foreach(gg->guarded_objects, gcguard_mark_i, 0);
+}
+
+static void
+gcguard_free(void* ptr)
+{
+  struct gcguard *gg = (struct gcguard *)ptr;
+  st_free_table(gg->guarded_objects);
+}
+
+static size_t
+gcguard_memsize(const void* ptr)
+{
+  const struct gcguard *gg = (const struct gcguard *)ptr;
+  return st_memsize(gg->guarded_objects);
+}
+
+static rb_data_type_t gcguard_data_type = {
+  "PyCall::gcguard",
+  {
+    gcguard_mark,
+    gcguard_free,
+    gcguard_memsize,
+  },
+#ifdef RUBY_TYPED_FREE_IMMEDIATELY
+  0, 0, RUBY_TYPED_FREE_IMMEDIATELY
+#endif
+};
+
+static void
+gcguard_aset(VALUE gcguard, PyObject *pyptr, VALUE rbobj)
+{
+  struct gcguard *gg;
+  TypedData_Get_Struct(gcguard, struct gcguard, &gcguard_data_type, gg);
+
+  st_insert(gg->guarded_objects, (st_data_t)pyptr, (st_data_t)rbobj);
+}
+
+static void
+gcguard_delete(VALUE gcguard, PyObject *pyptr)
+{
+  struct gcguard *gg;
+  st_data_t key, val;
+
+  TypedData_Get_Struct(gcguard, struct gcguard, &gcguard_data_type, gg);
+
+  key = (st_data_t)pyptr;
+  st_delete(gg->guarded_objects, &key, &val);
+}
+
 static ID id_gcguard_table;
 static PyObject *weakref_callback_pyobj;
 static PyObject *gcguard_weakref_destroyed(PyObject *self, PyObject *weakref);
@@ -21,15 +87,15 @@ gcguard_weakref_destroyed(PyObject *self, PyObject *weakref)
 void
 pycall_gcguard_aset(PyObject *pyobj, VALUE rbobj)
 {
-  VALUE table = rb_ivar_get(mPyCall, id_gcguard_table);
-  rb_hash_aset(table, PTR2NUM(pyobj), rbobj);
+  VALUE gcguard = rb_ivar_get(mPyCall, id_gcguard_table);
+  gcguard_aset(gcguard, pyobj, rbobj);
 }
 
 void
 pycall_gcguard_delete(PyObject *pyobj)
 {
-  VALUE table = rb_ivar_get(mPyCall, id_gcguard_table);
-  rb_hash_delete(table, PTR2NUM(pyobj));
+  VALUE gcguard = rb_ivar_get(mPyCall, id_gcguard_table);
+  gcguard_delete(gcguard, pyobj);
 }
 
 void
@@ -64,11 +130,21 @@ pycall_gcguard_register(PyObject *pyobj, VALUE obj)
   pycall_gcguard_aset(wref, obj);
 }
 
+static VALUE
+gcguard_new(void)
+{
+  struct gcguard *gg;
+  VALUE obj = TypedData_Make_Struct(0, struct gcguard, &gcguard_data_type, gg);
+  gg->guarded_objects = st_init_numtable();
+
+  return obj;
+}
+
 void
 pycall_init_gcguard(void)
 {
   id_gcguard_table = rb_intern("gcguard_table");
-  rb_ivar_set(mPyCall, id_gcguard_table, rb_hash_new());
+  rb_ivar_set(mPyCall, id_gcguard_table, gcguard_new());
 
   weakref_callback_pyobj = Py_API(PyCFunction_NewEx)(&gcguard_weakref_callback_def, NULL, NULL);
 }