mirror of https://github.com/python/cpython
Patch by Charles G Waldman to avoid a sneaky memory leak in
_PyTuple_Resize(). In addition, a change suggested by Jeremy Hylton to limit the size of the free lists is also merged into this patch. Charles wrote initially: """ Test Case: run the following code: class Nothing: def __len__(self): return 5 def __getitem__(self, i): if i < 3: return i else: raise IndexError, i def g(a,*b,**c): return for x in xrange(1000000): g(*Nothing()) and watch Python's memory use go up and up. Diagnosis: The analysis begins with the call to PySequence_Tuple at line 1641 in ceval.c - the argument to g is seen to be a sequence but not a tuple, so it needs to be converted from an abstract sequence to a concrete tuple. PySequence_Tuple starts off by creating a new tuple of length 5 (line 1122 in abstract.c). Then at line 1149, since only 3 elements were assigned, _PyTuple_Resize is called to make the 5-tuple into a 3-tuple. When we're all done the 3-tuple is decrefed, but rather than being freed it is placed on the free_tuples cache. The basic problem is that the 3-tuples are being added to the cache but never picked up again, since _PyTuple_Resize doesn't make use of the free_tuples cache. If you are resizing a 5-tuple to a 3-tuple and there is already a 3-tuple in free_tuples[3], instead of using this tuple, _PyTuple_Resize will realloc the 5-tuple to a 3-tuple. It would more efficient to use the existing 3-tuple and cache the 5-tuple. By making _PyTuple_Resize aware of the free_tuples (just as PyTuple_New), we not only save a few calls to realloc, but also prevent this misbehavior whereby tuples are being added to the free_tuples list but never properly "recycled". """ And later: """ This patch replaces my submission of Sun, 16 Apr and addresses Jeremy Hylton's suggestions that we also limit the size of the free tuple list. I chose 2000 as the maximum number of tuples of any particular size to save. There was also a problem with the previous version of this patch causing a core dump if Python was built with Py_TRACE_REFS. This is fixed in the below version of the patch, which uses tupledealloc instead of _Py_Dealloc. """
This commit is contained in:
parent
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commit
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@ -33,15 +33,20 @@ PERFORMANCE OF THIS SOFTWARE.
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#include "Python.h"
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/* Speed optimization to avoid frequent malloc/free of small tuples */
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#ifndef MAXSAVESIZE
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#define MAXSAVESIZE 20
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#define MAXSAVESIZE 20 /* Largest tuple to save on free list */
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#endif
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#ifndef MAXSAVEDTUPLES
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#define MAXSAVEDTUPLES 2000 /* Maximum number of tuples of each size to save */
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#endif
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#if MAXSAVESIZE > 0
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/* Entries 1 upto MAXSAVESIZE are free lists, entry 0 is the empty
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/* Entries 1 up to MAXSAVESIZE are free lists, entry 0 is the empty
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tuple () of which at most one instance will be allocated.
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*/
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static PyTupleObject *free_tuples[MAXSAVESIZE];
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static int num_free_tuples[MAXSAVESIZE];
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#endif
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#ifdef COUNT_ALLOCS
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int fast_tuple_allocs;
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@ -71,6 +76,7 @@ PyTuple_New(size)
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(op = free_tuples[size]) != NULL)
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{
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free_tuples[size] = (PyTupleObject *) op->ob_item[0];
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num_free_tuples[size]--;
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#ifdef COUNT_ALLOCS
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fast_tuple_allocs++;
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#endif
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@ -104,6 +110,7 @@ PyTuple_New(size)
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#if MAXSAVESIZE > 0
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if (size == 0) {
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free_tuples[0] = op;
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++num_free_tuples[0];
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Py_INCREF(op); /* extra INCREF so that this is never freed */
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}
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#endif
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@ -171,16 +178,17 @@ tupledealloc(op)
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register PyTupleObject *op;
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{
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register int i;
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register int len = op->ob_size;
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Py_TRASHCAN_SAFE_BEGIN(op)
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if (op->ob_size > 0) {
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i = op->ob_size;
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if (len > 0) {
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i = len;
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while (--i >= 0)
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Py_XDECREF(op->ob_item[i]);
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#if MAXSAVESIZE > 0
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if (op->ob_size < MAXSAVESIZE) {
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op->ob_item[0] = (PyObject *) free_tuples[op->ob_size];
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free_tuples[op->ob_size] = op;
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if (len < MAXSAVESIZE && num_free_tuples[len] < MAXSAVEDTUPLES) {
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op->ob_item[0] = (PyObject *) free_tuples[len];
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num_free_tuples[len]++;
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free_tuples[len] = op;
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goto done; /* return */
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}
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#endif
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@ -469,14 +477,49 @@ _PyTuple_Resize(pv, newsize, last_is_sticky)
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Py_XDECREF(v->ob_item[i]);
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v->ob_item[i] = NULL;
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}
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sv = (PyTupleObject *)
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realloc((char *)v,
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sizeof(PyTupleObject) + newsize * sizeof(PyObject *));
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*pv = (PyObject *) sv;
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if (sv == NULL) {
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PyMem_DEL(v);
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PyErr_NoMemory();
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return -1;
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#if MAXSAVESIZE > 0
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if (newsize == 0 && free_tuples[0]) {
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num_free_tuples[0]--;
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sv = free_tuples[0];
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sv->ob_size = 0;
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Py_INCREF(sv);
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#ifdef COUNT_ALLOCS
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tuple_zero_allocs++;
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#endif
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tupledealloc(v);
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*pv = (PyObject*) sv;
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return 0;
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}
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if (0 < newsize && newsize < MAXSAVESIZE &&
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(sv = free_tuples[newsize]) != NULL)
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{
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free_tuples[newsize] = (PyTupleObject *) sv->ob_item[0];
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num_free_tuples[newsize]--;
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#ifdef COUNT_ALLOCS
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fast_tuple_allocs++;
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#endif
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#ifdef Py_TRACE_REFS
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sv->ob_type = &PyTuple_Type;
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#endif
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for (i = 0; i < newsize; ++i){
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sv->ob_item[i] = v->ob_item[i];
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v->ob_item[i] = NULL;
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}
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sv->ob_size = v->ob_size;
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tupledealloc(v);
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*pv = (PyObject *) sv;
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} else
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#endif
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{
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sv = (PyTupleObject *)
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realloc((char *)v,
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sizeof(PyTupleObject) + newsize * sizeof(PyObject *));
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*pv = (PyObject *) sv;
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if (sv == NULL) {
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PyMem_DEL(v);
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PyErr_NoMemory();
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return -1;
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}
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}
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_Py_NewReference((PyObject *)sv);
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for (i = sv->ob_size; i < newsize; i++)
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