Hi Paul,
Paul Keogh schrieb:
Hi,
I've experienced a livelock (ie. CPU bound) bug in the conn_pool_get()
function in http.c.
I'm sending lots of HTTP requests to a server that closes the connection
after every request.
After 5/6/7 requests the conn_pool_get() function gets stuck in an
infinite look and never returns;
hmm, this should be something different.
From looking at the code;
do {
retry = 0;
ˆˆˆˆˆˆˆˆˆˆˆˆ
here we reset retry... and when no conns in dict found than no retry
will be performed.
key = conn_pool_key(host, port);
mutex_lock(conn_pool_lock);
list = dict_get(conn_pool, key);
if (list != NULL)
conn = gwlist_extract_first(list);
mutex_unlock(conn_pool_lock);
/*
* Note: we don't hold conn_pool_lock when we
check/destroy/unregister
* connection because otherwise we can deadlock! And it's
even better
* not to delay other threads while we check connection.
*/
if (conn != NULL) {
#ifdef USE_KEEPALIVE
/* unregister our server disconnect callback */
conn_unregister(conn);
#endif
/*
* Check whether the server has closed the connection while
* it has been in the pool.
*/
conn_wait(conn, 0);
if (conn_eof(conn) || conn_error(conn)) {
debug("gwlib.http", 0, "HTTP:conn_pool_get: Server
closed connection, destroying it <%s><%p><fd:%d>.",
octstr_get_cstr(key), conn, conn_get_id(conn));
conn_destroy(conn);
retry = 1;
conn = NULL;
}
}
octstr_destroy(key);
} while(retry == 1);
* The retry variable is set to 1 because the server has closed the
connection
right
* This forces the while loop to run
right
* There are no conns in the list for this host/port combination so conn
is always NULL subsequently. The
retry variable is not reset to 0 on this condition and the loop locks
up.
not true. see above...
* One solution is to reset retry to 0 on a NULL conn -
if (conn != NULL) {
#ifdef USE_KEEPALIVE
....
}
else
retry = 0;
This does appear to fix the issue in my test harness.
Comments ?
I don't know why this change should help. could you please try debug it
further?
Thanks,
Alex
