Dear,
This is the double circle queue. But the operations are not enqueue
the circle queue.
Below is the standard operations:
if (!base->server_head) {
ns->next = ns->prev = ns;
base->server_head = ns;
} else {
ns->next = base->server_head->next;
ns->prev = base->server_head;
base->server_head->next = ns;
if (base->server_head->prev == base->server_head) {
base->server_head->prev = ns;
}else{
base->server_head->next->next-prev = ns;
}
}
On 12/22/11, wang qin <scpl0...@gmail.com> wrote:
> Dear,
>
> This code snippet comes from libevent-2.0.13. The list operation is
> the same. I think it does not have any bugs.
>
> yrs,
>
>
>
> /* insert this nameserver into the list of them */
> if (!base->server_head) {
> ns->next = ns->prev = ns;
> base->server_head = ns;
> } else {
> ns->next = base->server_head->next;
> ns->prev = base->server_head;
> base->server_head->next = ns;
> if (base->server_head->prev == base->server_head) {
> base->server_head->prev = ns;
> }
> }
>
>
> On 12/22/11, Nick Mathewson <ni...@freehaven.net> wrote:
>> On Wed, Dec 21, 2011 at 7:53 AM, wang qin <scpl0...@gmail.com> wrote:
>>>
>>> Dear,
>>>
>>> I do not understand of the list operation of the
>>> _evdns_nameserver_add_impl.
>>>
>>> How to understand this snippet?
>>>
>>> Best is figures and notes.
>>>
>>>
>>>
>>> Thank you very much!
>>>
>>>
>>> /* insert this nameserver into the list of them */
>>> if (!server_head) {
>>> ns->next = ns->prev = ns;
>>> server_head = ns;
>>> } else {
>>> ns->next = server_head->next;
>>> ns->prev = server_head;
>>> server_head->next = ns;
>>> if (server_head->prev == server_head) {
>>> server_head->prev = ns;
>>> }
>>> }
>>
>> It looks like it's supposed to be a circular doubly linked list to me.
>> If the list is empty, then the new nameserver is inserted as the sole
>> node, and its prev and next pointers are set to itself (to make the
>> list circular). But if the list is notempty, we insert the new
>> nameserver after the current head (server_head).
>>
>> It looks like there's a possible bug there; I don't see anything that
>> points ns->next->prev at ns. If that's so, the best solution here is
>> probably to replace the whole thing evdns_base.server_head thing with
>> a CIRCLEQ or such.
>>
>> (FWIW, this looks like really old code; Libevent 2.0 is the version
>> folks should be using. Libevent 1.4 is not under active development.)
>>
>> yrs,
>> --
>> Nick
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>>
>
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