* Bulletproof the method for detecting mutations during iteration.

The previous approach was too easily fooled (a rotate() sufficed).

* Use it->counter to determine when iteration is complete.  The
  previous approach was too complex.

* Strengthen an assertion and add a comment here or there.
This commit is contained in:
Raymond Hettinger 2004-10-02 00:43:13 +00:00
parent 77e8bf1ca4
commit d1b3d88bf3
1 changed files with 32 additions and 18 deletions

View File

@ -70,6 +70,7 @@ typedef struct {
int leftindex; /* in range(BLOCKLEN) */
int rightindex; /* in range(BLOCKLEN) */
int len;
long state; /* incremented whenever the indices move */
PyObject *weakreflist; /* List of weak references */
} dequeobject;
@ -98,6 +99,7 @@ deque_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
deque->leftindex = CENTER + 1;
deque->rightindex = CENTER;
deque->len = 0;
deque->state = 0;
deque->weakreflist = NULL;
return (PyObject *)deque;
@ -108,6 +110,7 @@ deque_append(dequeobject *deque, PyObject *item)
{
deque->rightindex++;
deque->len++;
deque->state++;
if (deque->rightindex == BLOCKLEN) {
block *b = newblock(deque->rightblock, NULL);
if (b == NULL)
@ -129,6 +132,7 @@ deque_appendleft(dequeobject *deque, PyObject *item)
{
deque->leftindex--;
deque->len++;
deque->state++;
if (deque->leftindex == -1) {
block *b = newblock(NULL, deque->leftblock);
if (b == NULL)
@ -158,6 +162,7 @@ deque_pop(dequeobject *deque, PyObject *unused)
item = deque->rightblock->data[deque->rightindex];
deque->rightindex--;
deque->len--;
deque->state++;
if (deque->rightindex == -1) {
if (deque->len == 0) {
@ -193,6 +198,7 @@ deque_popleft(dequeobject *deque, PyObject *unused)
item = deque->leftblock->data[deque->leftindex];
deque->leftindex++;
deque->len--;
deque->state++;
if (deque->leftindex == BLOCKLEN) {
if (deque->len == 0) {
@ -229,6 +235,7 @@ deque_extend(dequeobject *deque, PyObject *iterable)
while ((item = PyIter_Next(it)) != NULL) {
deque->rightindex++;
deque->len++;
deque->state++;
if (deque->rightindex == BLOCKLEN) {
block *b = newblock(deque->rightblock, NULL);
if (b == NULL) {
@ -264,6 +271,7 @@ deque_extendleft(dequeobject *deque, PyObject *iterable)
while ((item = PyIter_Next(it)) != NULL) {
deque->leftindex--;
deque->len++;
deque->state++;
if (deque->leftindex == -1) {
block *b = newblock(NULL, deque->leftblock);
if (b == NULL) {
@ -341,13 +349,14 @@ deque_clear(dequeobject *deque)
{
PyObject *item;
while (deque_len(deque)) {
while (deque->len) {
item = deque_pop(deque, NULL);
assert (item != NULL);
Py_DECREF(item);
}
assert(deque->leftblock == deque->rightblock &&
deque->leftindex > deque->rightindex);
deque->leftindex - 1 == deque->rightindex &&
deque->len == 0);
return 0;
}
@ -822,8 +831,8 @@ typedef struct {
int index;
block *b;
dequeobject *deque;
int len;
int counter;
long state; /* state when the iterator is created */
int counter; /* number of items remaining for iteration */
} dequeiterobject;
PyTypeObject dequeiter_type;
@ -840,7 +849,7 @@ deque_iter(dequeobject *deque)
it->index = deque->leftindex;
Py_INCREF(deque);
it->deque = deque;
it->len = deque->len;
it->state = deque->state;
it->counter = deque->len;
return (PyObject *)it;
}
@ -856,24 +865,27 @@ static PyObject *
dequeiter_next(dequeiterobject *it)
{
PyObject *item;
if (it->b == it->deque->rightblock && it->index > it->deque->rightindex)
if (it->counter == 0)
return NULL;
if (it->len != it->deque->len) {
it->len = -1; /* Make this state sticky */
if (it->deque->state != it->state) {
it->counter = 0;
PyErr_SetString(PyExc_RuntimeError,
"deque changed size during iteration");
"deque mutated during iteration");
return NULL;
}
assert (!(it->b == it->deque->rightblock &&
it->index > it->deque->rightindex));
item = it->b->data[it->index];
it->index++;
if (it->index == BLOCKLEN && it->b->rightlink != NULL) {
it->counter--;
if (it->index == BLOCKLEN && it->counter > 0) {
assert (it->b->rightlink != NULL);
it->b = it->b->rightlink;
it->index = 0;
}
it->counter--;
Py_INCREF(item);
return item;
}
@ -938,7 +950,7 @@ deque_reviter(dequeobject *deque)
it->index = deque->rightindex;
Py_INCREF(deque);
it->deque = deque;
it->len = deque->len;
it->state = deque->state;
it->counter = deque->len;
return (PyObject *)it;
}
@ -947,24 +959,26 @@ static PyObject *
dequereviter_next(dequeiterobject *it)
{
PyObject *item;
if (it->b == it->deque->leftblock && it->index < it->deque->leftindex)
if (it->counter == 0)
return NULL;
if (it->len != it->deque->len) {
it->len = -1; /* Make this state sticky */
if (it->deque->state != it->state) {
it->counter = 0;
PyErr_SetString(PyExc_RuntimeError,
"deque changed size during iteration");
"deque mutated during iteration");
return NULL;
}
assert (!(it->b == it->deque->leftblock &&
it->index < it->deque->leftindex));
item = it->b->data[it->index];
it->index--;
if (it->index == -1 && it->b->leftlink != NULL) {
it->counter--;
if (it->index == -1 && it->counter > 0) {
assert (it->b->leftlink != NULL);
it->b = it->b->leftlink;
it->index = BLOCKLEN - 1;
}
it->counter--;
Py_INCREF(item);
return item;
}