commit 91c58013be735584acc674a60bb18d1efb38f25a Author: Roger Dingledine <arma@torproject.org> Date: Wed Apr 13 01:08:17 2016 -0400 avoid following through on a consensus fetch if we have one already arriving --- src/or/circuituse.c | 19 ++++++++++++++++++ src/or/networkstatus.c | 53 ++++++++++++++++++++++++++++++++++---------------- src/or/networkstatus.h | 1 + 3 files changed, 56 insertions(+), 17 deletions(-) diff --git a/src/or/circuituse.c b/src/or/circuituse.c index 31003ea..f32763a 100644 --- a/src/or/circuituse.c +++ b/src/or/circuituse.c @@ -2355,6 +2355,25 @@ connection_ap_handshake_attach_circuit(entry_connection_t *conn) /* we're a general conn */ origin_circuit_t *circ=NULL; + /* Are we linked to a dir conn that aims to fetch a consensus? + * We check here because this conn might no longer be needed. */ + if (base_conn->linked_conn && + base_conn->linked_conn->type == CONN_TYPE_DIR && + base_conn->linked_conn->purpose == DIR_PURPOSE_FETCH_CONSENSUS) { + + /* Yes we are. Is there a consensus fetch farther along than us? */ + if (networkstatus_consensus_is_already_downloading( + TO_DIR_CONN(base_conn->linked_conn)->requested_resource)) { + /* We're doing the "multiple consensus fetch attempts" game from + * proposal 210, and we're late to the party. Just close this conn. + * The circuit and TLS conn that we made will time out after a while + * if nothing else wants to use them. */ + log_info(LD_DIR, "Closing extra consensus fetch (to %s) since one " + "is already downloading.", base_conn->linked_conn->address); + return -1; + } + } + if (conn->chosen_exit_name) { const node_t *node = node_get_by_nickname(conn->chosen_exit_name, 1); int opt = conn->chosen_exit_optional; diff --git a/src/or/networkstatus.c b/src/or/networkstatus.c index 51c985e..e90603e 100644 --- a/src/or/networkstatus.c +++ b/src/or/networkstatus.c @@ -1349,27 +1349,46 @@ networkstatus_consensus_has_excess_connections(void) return 0; } +/* Is there a consensus fetch for flavor <b>resource</b> that's far + * enough along to be attached to a circuit? */ +int +networkstatus_consensus_is_already_downloading(const char *resource) +{ + int answer = 0; + + /* First, get a list of all the dir conns that are fetching a consensus, + * fetching *this* consensus, and are in state "reading" (meaning they + * have already flushed their request onto the socks connection). */ + smartlist_t *fetching_conns = + connection_dir_list_by_purpose_resource_and_state( + DIR_PURPOSE_FETCH_CONSENSUS, resource, DIR_CONN_STATE_CLIENT_READING); + + /* Then, walk through each conn, to see if its linked socks connection + * is in an attached state. We have to check this separately, since with + * the optimistic data feature, fetches can send their request to the + * socks connection and go into state 'reading', even before they're + * attached to any circuit. */ + SMARTLIST_FOREACH_BEGIN(fetching_conns, dir_connection_t *, dirconn) { + /* Do any of these other dir conns have a linked socks conn that is + * attached to a circuit already? */ + connection_t *base = TO_CONN(dirconn); + if (base->linked_conn && + base->linked_conn->type == CONN_TYPE_AP && + !AP_CONN_STATE_IS_UNATTACHED(base->linked_conn->state)) + answer = 1; + } SMARTLIST_FOREACH_END(dirconn); + smartlist_free(fetching_conns); + + return answer; +} + /* Is tor currently downloading a consensus of the usable flavor? */ int networkstatus_consensus_is_downloading_usable_flavor(void) { - const char *usable_resource = networkstatus_get_flavor_name( - usable_consensus_flavor()); - const int consens_conn_usable_count = - connection_dir_count_by_purpose_and_resource( - DIR_PURPOSE_FETCH_CONSENSUS, - usable_resource); - - const int connect_consens_conn_usable_count = - connection_dir_count_by_purpose_resource_and_state( - DIR_PURPOSE_FETCH_CONSENSUS, - usable_resource, - DIR_CONN_STATE_CONNECTING); - if (connect_consens_conn_usable_count < consens_conn_usable_count) { - return 1; - } - - return 0; + const char *resource = + networkstatus_get_flavor_name(usable_consensus_flavor()); + return networkstatus_consensus_is_already_downloading(resource); } /** Given two router status entries for the same router identity, return 1 if diff --git a/src/or/networkstatus.h b/src/or/networkstatus.h index f2f8af5..e1cd10b 100644 --- a/src/or/networkstatus.h +++ b/src/or/networkstatus.h @@ -76,6 +76,7 @@ int networkstatus_consensus_can_use_multiple_directories( int networkstatus_consensus_can_use_extra_fallbacks( const or_options_t *options); int networkstatus_consensus_has_excess_connections(void); +int networkstatus_consensus_is_already_downloading(const char *resource); int networkstatus_consensus_is_downloading_usable_flavor(void); #define NSSET_FROM_CACHE 1