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New comments. Rewrote has_finalizer() as a sequence of ifs instead of

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squashed-together conditional operators; makes it much easier to step
thru in the debugger, and to set a breakpoint on the only dangerous
path.
This commit is contained in:
Tim Peters 2003-04-05 17:35:54 +00:00
parent 93ad66dea9
commit 86b993b6cf
1 changed files with 21 additions and 6 deletions
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27
Modules/gcmodule.c
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@ -339,13 +339,26 @@ move_unreachable(PyGC_Head *young, PyGC_Head *unreachable)
} }
} }
/* return true if object has a finalization method */ /* Return true if object has a finalization method.
* CAUTION: An instance of an old-style class has to be checked for a
*__del__ method, and that can cause arbitrary Python code to get executed
* via the class's __getattr__ hook (if any). This function can therefore
* mutate the object graph, and that's been the source of subtle bugs.
*/
static int static int
has_finalizer(PyObject *op) has_finalizer(PyObject *op)
{ {
return PyInstance_Check(op) ? PyObject_HasAttr(op, delstr) : if (PyInstance_Check(op)) {
PyType_HasFeature(op->ob_type, Py_TPFLAGS_HEAPTYPE) ? /* This is the dangerous path: hasattr can invoke
op->ob_type->tp_del != NULL : 0; * the class __getattr__(), and that can do anything.
*/
assert(delstr != NULL);
return PyObject_HasAttr(op, delstr);
}
else if (PyType_HasFeature(op->ob_type, Py_TPFLAGS_HEAPTYPE))
return op->ob_type->tp_del != NULL;
else
return 0;
} }
/* Move all objects out of unreachable and into collectable or finalizers. /* Move all objects out of unreachable and into collectable or finalizers.
@ -586,8 +599,10 @@ collect(int generation)
* instance objects with __del__ methods. * instance objects with __del__ methods.
* *
* Move each object into the collectable set or the finalizers set. * Move each object into the collectable set or the finalizers set.
* It's possible that a classic class with a getattr() hook will * Because we need to check for __del__ methods on instances of
* be revived or deallocated in this step. * classic classes, arbitrary Python code may get executed by
* getattr hooks: that may resurrect or deallocate (via refcount
* falling to 0) unreachable objects, so this is very delicate.
*/ */
gc_list_init(&collectable); gc_list_init(&collectable);
gc_list_init(&finalizers); gc_list_init(&finalizers);