曾经研究memcached的时候发现它的状态机里有一个很隐蔽的逻辑bug很难触发就随手在issue里提了个bug,现在已经被合并到memcached主干上了
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on line 3857
if
update_event()
return
false
and the connection's bind event is still EV_READ
c->state will be conn_closing and stop will be
true
if
no
more
bytes comes, the socket will never be cleanup?
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就是说在memcache.c的3857行如果update_event()返回false并且 连接的bind event依旧是EV_READ
c->state将会是conn_closing 而且 stop的值将会是true
这时如果没有更多的数据从socket上传入socket将永远不会被清理造成泄漏
Status: Fixed:
https://code.google.com/p/memcached/issues/detail?id=261&can=1&q=auxtenwpc%40gmail.com
https://github.com/memcached/memcached/commit/b2734f8321230bd52e36df7f82a6b1d71532e496
过了两年才有人鸟我然后被合并到主干上了:-)
Reported by auxten...@gmail.com, Mar 17, 2012
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3839
case
conn_new_cmd:
3840 /* Only process nreqs at a
time
to avoid starving other
3841 connections */
3842
3843 --nreqs;
3844
if
(nreqs >= 0) {
3845 reset_cmd_handler(c);
3846 }
else
{
3847 pthread_mutex_lock(&c->thread->stats.mutex);
3848 c->thread->stats.conn_yields++;
3849 pthread_mutex_unlock(&c->thread->stats.mutex);
3850
if
(c->rbytes > 0) {
3851 /* We have already
read
in
data into the input buffer,
3852 so libevent will most likely not signal
read
events
3853 on the socket (unless
more
data is available. As a
3854 hack we should just put
in
a request to write data,
3855 because that should be possible ;-)
3856 */
3857
if
(!update_event(c, EV_WRITE | EV_PERSIST)) {
3858
if
(settings.verbose > 0)
3859 fprintf(stderr,
"Couldn't update event\n"
);
3860 conn_set_state(c, conn_closing);
3861 }
3862 }
3863 stop =
true
;
3864 }
3865
break
;
on line 3857
if
update_event()
return
false
and the connection's bind event is still EV_READ
c->state will be conn_closing and stop will be
true
if
no
more
bytes comes, the socket will never be cleanup?
so i think there need a patch
--- a
/memcached
.c
+++ b
/memcached
.c
@@ -3858,6 +3858,7 @@ static void drive_machine(conn *c) {
if
(settings.verbose > 0)
fprintf(stderr,
"Couldn't update event\n"
);
conn_set_state(c, conn_closing);
+
break
;
}
}
stop =
true
;
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Project Member #1 dorma...@rydia.net
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Wow, two years old... and it looks correct to me. If that update_event fails the connection might zombie. It
's very hard for that to fail and it'
s been that way forever.
Pushed a commit
for
the next release.
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本文转自 xjtuhit 51CTO博客，原文链接:http://blog.51cto.com/51reboot/1560493
