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a4dd011259
and reported to python-dev: because we were calling dict_resize() in PyDict_Next(), and because GC's dict_traverse() uses PyDict_Next(), and because PyTuple_New() can cause GC, and because dict_items() calls PyTuple_New(), it was possible for dict_items() to have the dict resized right under its nose. The solution is convoluted, and touches several places: keys(), values(), items(), popitem(), PyDict_Next(), and PyDict_SetItem(). There are two parts to it. First, we no longer call dict_resize() in PyDict_Next(), which seems to solve the immediate problem. But then PyDict_SetItem() must have a different policy about when *it* calls dict_resize(), because we want to guarantee (e.g. for an algorithm that Jeremy uses in the compiler) that you can loop over a dict using PyDict_Next() and make changes to the dict as long as those changes are only value replacements for existing keys using PyDict_SetItem(). This is done by resizing *after* the insertion instead of before, and by remembering the size before we insert the item, and if the size is still the same, we don't bother to even check if we might need to resize. An additional detail is that if the dict starts out empty, we must still resize it before the insertion. That was the first part. :-) The second part is to make keys(), values(), items(), and popitem() safe against side effects on the dict caused by allocations, under the assumption that if the GC can cause arbitrary Python code to run, it can cause other threads to run, and it's not inconceivable that our dict could be resized -- it would be insane to write code that relies on this, but not all code is sane. Now, I have this nagging feeling that the loops in lookdict probably are blissfully assuming that doing a simple key comparison does not change the dict's size. This is not necessarily true (the keys could be class instances after all). But that's a battle for another day. |
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| .. | ||
| .cvsignore | ||
| abstract.c | ||
| bufferobject.c | ||
| cellobject.c | ||
| classobject.c | ||
| cobject.c | ||
| complexobject.c | ||
| dictobject.c | ||
| fileobject.c | ||
| floatobject.c | ||
| frameobject.c | ||
| funcobject.c | ||
| intobject.c | ||
| listobject.c | ||
| longobject.c | ||
| methodobject.c | ||
| moduleobject.c | ||
| object.c | ||
| obmalloc.c | ||
| rangeobject.c | ||
| sliceobject.c | ||
| stringobject.c | ||
| tupleobject.c | ||
| typeobject.c | ||
| unicodectype.c | ||
| unicodeobject.c | ||
| unicodetype_db.h | ||
| xxobject.c | ||