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https://gitlab.torproject.org/tpo/core/tor.git
synced 2024-11-10 13:13:44 +01:00
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.
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c5a3e2ca44
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@ -410,6 +410,27 @@ connection_unlink(connection_t *conn)
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connection_free(conn);
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}
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/**
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* Callback: used to activate read events for all linked connections, so
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* libevent knows to call their read callbacks. This callback run as a
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* postloop event, so that the events _it_ activates don't happen until
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* Libevent has a chance to check for other events.
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*/
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static void
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schedule_active_linked_connections_cb(mainloop_event_t *event, void *arg)
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{
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(void)event;
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(void)arg;
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/* All active linked conns should get their read events activated,
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* so that libevent knows to run their callbacks. */
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SMARTLIST_FOREACH(active_linked_connection_lst, connection_t *, conn,
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event_active(conn->read_event, EV_READ, 1));
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}
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/** Event that invokes schedule_active_linked_connections_cb. */
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static mainloop_event_t *schedule_active_linked_connections_event = NULL;
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/** Initialize the global connection list, closeable connection list,
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* and active connection list. */
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STATIC void
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@ -803,10 +824,7 @@ connection_start_reading_from_linked_conn(connection_t *conn)
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if (!conn->active_on_link) {
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conn->active_on_link = 1;
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smartlist_add(active_linked_connection_lst, conn);
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/* make sure that the event_base_loop() function exits at
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* the end of its run through the current connections, so we can
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* activate read events for linked connections. */
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tell_event_loop_to_run_external_code();
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mainloop_event_activate(schedule_active_linked_connections_event);
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} else {
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tor_assert(smartlist_contains(active_linked_connection_lst, conn));
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}
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@ -2579,6 +2597,11 @@ do_main_loop(void)
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initialize_periodic_events();
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}
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if (!schedule_active_linked_connections_event) {
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schedule_active_linked_connections_event =
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mainloop_event_postloop_new(schedule_active_linked_connections_cb, NULL);
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}
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/* initialize dns resolve map, spawn workers if needed */
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if (dns_init() < 0) {
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if (get_options()->ServerDNSAllowBrokenConfig)
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@ -2783,17 +2806,12 @@ run_main_loop_once(void)
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errno = 0;
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#endif
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/* All active linked conns should get their read events activated,
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* so that libevent knows to run their callbacks. */
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SMARTLIST_FOREACH(active_linked_connection_lst, connection_t *, conn,
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event_active(conn->read_event, EV_READ, 1));
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if (get_options()->MainloopStats) {
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/* We always enforce that EVLOOP_ONCE is passed to event_base_loop() if we
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* are collecting main loop statistics. */
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called_loop_once = 1;
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} else {
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called_loop_once = smartlist_len(active_linked_connection_lst) ? 1 : 0;
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called_loop_once = 0;
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}
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/* Make sure we know (about) what time it is. */
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@ -3496,6 +3514,7 @@ tor_free_all(int postfork)
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tor_event_free(shutdown_did_not_work_event);
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tor_event_free(initialize_periodic_events_event);
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mainloop_event_free(directory_all_unreachable_cb_event);
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mainloop_event_free(schedule_active_linked_connections_event);
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#ifdef HAVE_SYSTEMD_209
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periodic_timer_free(systemd_watchdog_timer);
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