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ares_cancel(): cancel requests safely 

An invocation of ares_cancel() walks through the request list, calling
the callbacks of all pending requests on a channel. Previously, if such
a callback added a new request to the channel, the request list might
not end up empty, causing an abort by assertion failure. The present
commit ensures that precisely all requests present upon entry of
ares_cancel() are cancelled, and that adding new requests through
callbacks is safe.
This commit is contained in:
Alexander Klauer 2013-04-08 11:48:43 +02:00 committed by Daniel Stenberg
parent 127d4cb357
commit 54faf09da6
1 changed files with 21 additions and 21 deletions
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42
ares_cancel.c
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@ -26,33 +26,33 @@
void ares_cancel(ares_channel channel)
{
struct query *query;
struct list_node list_head_copy;
struct list_node* list_head;
struct list_node* list_node;
int i;
list_head = &(channel->all_queries);
for (list_node = list_head->next; list_node != list_head; )
if (!ares__is_list_empty(&(channel->all_queries)))
{
query = list_node->data;
list_node = list_node->next; /* since we're deleting the query */
query->callback(query->arg, ARES_ECANCELLED, 0, NULL, 0);
ares__free_query(query);
/* Swap list heads, so that only those queries which were present on entry
* into this function are cancelled. New queries added by callbacks of
* queries being cancelled will not be cancelled themselves.
*/
list_head = &(channel->all_queries);
list_head_copy.prev = list_head->prev;
list_head_copy.next = list_head->next;
list_head_copy.prev->next = &list_head_copy;
list_head_copy.next->prev = &list_head_copy;
list_head->prev = list_head;
list_head->next = list_head;
for (list_node = list_head_copy.next; list_node != &list_head_copy; )
{
query = list_node->data;
list_node = list_node->next; /* since we're deleting the query */
query->callback(query->arg, ARES_ECANCELLED, 0, NULL, 0);
ares__free_query(query);
}
}
#ifndef NDEBUG
/* Freeing the query should remove it from all the lists in which it sits,
* so all query lists should be empty now.
*/
assert(ares__is_list_empty(&(channel->all_queries)));
for (i = 0; i < ARES_QID_TABLE_SIZE; i++)
{
assert(ares__is_list_empty(&(channel->queries_by_qid[i])));
}
for (i = 0; i < ARES_TIMEOUT_TABLE_SIZE; i++)
{
assert(ares__is_list_empty(&(channel->queries_by_timeout[i])));
}
#endif
if (!(channel->flags & ARES_FLAG_STAYOPEN))
if (!(channel->flags & ARES_FLAG_STAYOPEN) && ares__is_list_empty(&(channel->all_queries)))
{
if (channel->servers)
{