Make PyDict_Next safe to use for loops that merely modify the values
associated with existing dict keys. This is a variant of part of Michael Hudson's patch #409864 "lazy fix for Pings bizarre scoping crash".
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@ -92,7 +92,7 @@ The value ma_fill is the number of non-NULL keys (sum of Active and Dummy);
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ma_used is the number of non-NULL, non-dummy keys (== the number of non-NULL
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values == the number of Active items).
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To avoid slowing down lookups on a near-full table, we resize the table when
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it is more than half filled.
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it's two-thirds full.
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*/
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typedef struct dictobject dictobject;
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struct dictobject {
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@ -486,13 +486,15 @@ PyDict_SetItem(register PyObject *op, PyObject *key, PyObject *value)
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if (hash == -1)
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return -1;
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}
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/* if fill >= 2/3 size, double in size */
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if (mp->ma_fill*3 >= mp->ma_size*2) {
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if (dictresize(mp, mp->ma_used*2) != 0) {
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if (mp->ma_fill+1 > mp->ma_size)
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/* If fill >= 2/3 size, adjust size. Normally, this doubles the
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* size, but it's also possible for the dict to shrink (if ma_fill is
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* much larger than ma_used, meaning a lot of dict keys have been
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* deleted).
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* CAUTION: this resize logic must match the logic in PyDict_Next.
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*/
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if (mp->ma_fill*3 >= mp->ma_size*2 &&
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dictresize(mp, mp->ma_used*2) != 0)
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return -1;
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}
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}
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Py_INCREF(value);
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Py_INCREF(key);
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insertdict(mp, key, hash, value);
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@ -562,6 +564,11 @@ PyDict_Clear(PyObject *op)
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PyMem_DEL(table);
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}
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/* CAUTION: In general, it isn't safe to use PyDict_Next in a loop that
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* mutates the dict. One exception: it is safe if the loop merely changes
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* the values associated with the keys (but doesn't insert new keys or
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* delete keys), via PyDict_SetItem().
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*/
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int
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PyDict_Next(PyObject *op, int *ppos, PyObject **pkey, PyObject **pvalue)
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{
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@ -573,6 +580,23 @@ PyDict_Next(PyObject *op, int *ppos, PyObject **pkey, PyObject **pvalue)
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i = *ppos;
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if (i < 0)
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return 0;
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/* A hack to support loops that merely change values.
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* The problem: PyDict_SetItem() can either grow or shrink the dict
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* even when passed a key that's already in the dict. This was a
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* repeated source of subtle bugs, bad enough to justify a hack here.
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* Approach: If this is the first time PyDict_Next() is being called
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* (i==0), first figure out whether PyDict_SetItem() *will* change the
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* size, and if so get it changed before we start passing out internal
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* indices.
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*/
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if (i == 0) {
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/* This must be a clone of PyDict_SetItem's resize logic. */
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if (mp->ma_fill*3 >= mp->ma_size*2 &&
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dictresize(mp, mp->ma_used*2) != 0)
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return -1;
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}
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while (i < mp->ma_size && mp->ma_table[i].me_value == NULL)
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i++;
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*ppos = i+1;
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