commit 5719dfb48f87a54aeb5982ff03345303bc058ebb Author: Nick Mathewson nickm@torproject.org Date: Mon Apr 2 15:08:41 2018 -0400
Move the "activate linked connections" logic to a postloop event.
A linked connection_t is one that gets its I/O, not from the network, but from another connection_t. When such a connection has something to write, we want the corresponding connection to run its read callback ... but not immediately, to avoid infinite recursion and/or event loop starvation.
Previously we handled this case by activating the read events outside the event loop. Now we use the "postloop event" logic. This lets us simplify do_main_loop_once() a little. --- src/or/main.c | 39 +++++++++++++++++++++++++++++---------- 1 file changed, 29 insertions(+), 10 deletions(-)
diff --git a/src/or/main.c b/src/or/main.c index 4cc51de07..b499c1691 100644 --- a/src/or/main.c +++ b/src/or/main.c @@ -410,6 +410,27 @@ connection_unlink(connection_t *conn) connection_free(conn); }
+/** + * Callback: used to activate read events for all linked connections, so + * libevent knows to call their read callbacks. This callback run as a + * postloop event, so that the events _it_ activates don't happen until + * Libevent has a chance to check for other events. + */ +static void +schedule_active_linked_connections_cb(mainloop_event_t *event, void *arg) +{ + (void)event; + (void)arg; + + /* All active linked conns should get their read events activated, + * so that libevent knows to run their callbacks. */ + SMARTLIST_FOREACH(active_linked_connection_lst, connection_t *, conn, + event_active(conn->read_event, EV_READ, 1)); +} + +/** Event that invokes schedule_active_linked_connections_cb. */ +static mainloop_event_t *schedule_active_linked_connections_event = NULL; + /** Initialize the global connection list, closeable connection list, * and active connection list. */ STATIC void @@ -803,10 +824,7 @@ connection_start_reading_from_linked_conn(connection_t *conn) if (!conn->active_on_link) { conn->active_on_link = 1; smartlist_add(active_linked_connection_lst, conn); - /* make sure that the event_base_loop() function exits at - * the end of its run through the current connections, so we can - * activate read events for linked connections. */ - tell_event_loop_to_run_external_code(); + mainloop_event_activate(schedule_active_linked_connections_event); } else { tor_assert(smartlist_contains(active_linked_connection_lst, conn)); } @@ -2579,6 +2597,11 @@ do_main_loop(void) initialize_periodic_events(); }
+ if (!schedule_active_linked_connections_event) { + schedule_active_linked_connections_event = + mainloop_event_postloop_new(schedule_active_linked_connections_cb, NULL); + } + /* initialize dns resolve map, spawn workers if needed */ if (dns_init() < 0) { if (get_options()->ServerDNSAllowBrokenConfig) @@ -2783,17 +2806,12 @@ run_main_loop_once(void) errno = 0; #endif
- /* All active linked conns should get their read events activated, - * so that libevent knows to run their callbacks. */ - SMARTLIST_FOREACH(active_linked_connection_lst, connection_t *, conn, - event_active(conn->read_event, EV_READ, 1)); - if (get_options()->MainloopStats) { /* We always enforce that EVLOOP_ONCE is passed to event_base_loop() if we * are collecting main loop statistics. */ called_loop_once = 1; } else { - called_loop_once = smartlist_len(active_linked_connection_lst) ? 1 : 0; + called_loop_once = 0; }
/* Make sure we know (about) what time it is. */ @@ -3496,6 +3514,7 @@ tor_free_all(int postfork) tor_event_free(shutdown_did_not_work_event); tor_event_free(initialize_periodic_events_event); mainloop_event_free(directory_all_unreachable_cb_event); + mainloop_event_free(schedule_active_linked_connections_event);
#ifdef HAVE_SYSTEMD_209 periodic_timer_free(systemd_watchdog_timer);