Commit 5719dfb4 authored by Nick Mathewson's avatar Nick Mathewson 🤹
Browse files

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.
parent c5a3e2ca

src/or/main.c

+29 −10
Original line number Diff line number Diff line
@@ -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);