main: Add mainloop callback event flags

Implement the ability to set flags per events which influences the set up of
the event.

This commit only adds one flag which is "need network" meaning that the event
is not enabled if tor has disabled the network or if hibernation mode.

Signed-off-by: David Goulet <dgoulet@torproject.org>

changes/ticket25376_25762

@@ -0,0 +1,10 @@
+  o Major feature (main loop, CPU usage):
+    - Previously, tor would enable at startup all possible main loop event
+      regardless if it needed them. For instance, directory authorities
+      callbacks were fired up even for client only. We have now refactored this
+      whole interface to only enable the appropriate callbacks depending on what
+      are tor roles (client only, relay, hidden service, etc.). Furthermore,
+      these events now depend on DisableNetwork or the hibernation state in
+      order to enable them. This is a big step towards reducing client CPU usage
+      by reducing the amount of wake ups the daemon does. Closes ticket 25376
+      and 25762.

src/or/main.c

@@ -1362,54 +1362,65 @@ CALLBACK(write_stats_file);
 #undef CALLBACK
 
 /* Now we declare an array of periodic_event_item_t for each periodic event */
-#define CALLBACK(name, r) PERIODIC_EVENT(name, r)
+#define CALLBACK(name, r, f) PERIODIC_EVENT(name, r, f)
 
 STATIC periodic_event_item_t periodic_events[] = {
   /* Everyone needs to run those. */
-  CALLBACK(add_entropy, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(check_expired_networkstatus, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(clean_caches, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(fetch_networkstatus, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(heartbeat, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(launch_descriptor_fetches, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(reset_padding_counts, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(retry_listeners, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(rotate_x509_certificate, PERIODIC_EVENT_ROLE_ALL),
-  CALLBACK(write_stats_file, PERIODIC_EVENT_ROLE_ALL),
+  CALLBACK(add_entropy, PERIODIC_EVENT_ROLE_ALL, 0),
+  CALLBACK(check_expired_networkstatus, PERIODIC_EVENT_ROLE_ALL, 0),
+  CALLBACK(clean_caches, PERIODIC_EVENT_ROLE_ALL, 0),
+  CALLBACK(fetch_networkstatus, PERIODIC_EVENT_ROLE_ALL,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(heartbeat, PERIODIC_EVENT_ROLE_ALL, 0),
+  CALLBACK(launch_descriptor_fetches, PERIODIC_EVENT_ROLE_ALL,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(reset_padding_counts, PERIODIC_EVENT_ROLE_ALL, 0),
+  CALLBACK(retry_listeners, PERIODIC_EVENT_ROLE_ALL,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(rotate_x509_certificate, PERIODIC_EVENT_ROLE_ALL, 0),
+  CALLBACK(write_stats_file, PERIODIC_EVENT_ROLE_ALL, 0),
 
   /* Routers (bridge and relay) only. */
-  CALLBACK(check_descriptor, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(check_ed_keys, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(check_for_reachability_bw, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(check_onion_keys_expiry_time, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(clean_consdiffmgr, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(expire_old_ciruits_serverside, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(retry_dns, PERIODIC_EVENT_ROLE_ROUTER),
-  CALLBACK(rotate_onion_key, PERIODIC_EVENT_ROLE_ROUTER),
+  CALLBACK(check_descriptor, PERIODIC_EVENT_ROLE_ROUTER,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(check_ed_keys, PERIODIC_EVENT_ROLE_ROUTER, 0),
+  CALLBACK(check_for_reachability_bw, PERIODIC_EVENT_ROLE_ROUTER,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(check_onion_keys_expiry_time, PERIODIC_EVENT_ROLE_ROUTER, 0),
+  CALLBACK(clean_consdiffmgr, PERIODIC_EVENT_ROLE_ROUTER, 0),
+  CALLBACK(expire_old_ciruits_serverside, PERIODIC_EVENT_ROLE_ROUTER,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(retry_dns, PERIODIC_EVENT_ROLE_ROUTER, 0),
+  CALLBACK(rotate_onion_key, PERIODIC_EVENT_ROLE_ROUTER, 0),
 
   /* Authorities (bridge and directory) only. */
-  CALLBACK(downrate_stability, PERIODIC_EVENT_ROLE_AUTHORITIES),
-  CALLBACK(launch_reachability_tests, PERIODIC_EVENT_ROLE_AUTHORITIES),
-  CALLBACK(save_stability, PERIODIC_EVENT_ROLE_AUTHORITIES),
+  CALLBACK(downrate_stability, PERIODIC_EVENT_ROLE_AUTHORITIES, 0),
+  CALLBACK(launch_reachability_tests, PERIODIC_EVENT_ROLE_AUTHORITIES,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(save_stability, PERIODIC_EVENT_ROLE_AUTHORITIES, 0),
 
   /* Directory authority only. */
-  CALLBACK(check_authority_cert, PERIODIC_EVENT_ROLE_DIRAUTH),
+  CALLBACK(check_authority_cert, PERIODIC_EVENT_ROLE_DIRAUTH, 0),
 
   /* Relay only. */
-  CALLBACK(check_canonical_channels, PERIODIC_EVENT_ROLE_RELAY),
-  CALLBACK(check_dns_honesty, PERIODIC_EVENT_ROLE_RELAY),
+  CALLBACK(check_canonical_channels, PERIODIC_EVENT_ROLE_RELAY,
+           PERIODIC_EVENT_FLAG_NEED_NET),
+  CALLBACK(check_dns_honesty, PERIODIC_EVENT_ROLE_RELAY,
+           PERIODIC_EVENT_FLAG_NEED_NET),
 
   /* Hidden Service service only. */
-  CALLBACK(hs_service, PERIODIC_EVENT_ROLE_HS_SERVICE),
+  CALLBACK(hs_service, PERIODIC_EVENT_ROLE_HS_SERVICE,
+           PERIODIC_EVENT_FLAG_NEED_NET),
 
   /* Bridge only. */
-  CALLBACK(record_bridge_stats, PERIODIC_EVENT_ROLE_BRIDGE),
+  CALLBACK(record_bridge_stats, PERIODIC_EVENT_ROLE_BRIDGE, 0),
 
   /* Client only. */
-  CALLBACK(rend_cache_failure_clean, PERIODIC_EVENT_ROLE_CLIENT),
+  CALLBACK(rend_cache_failure_clean, PERIODIC_EVENT_ROLE_CLIENT, 0),
 
   /* Bridge Authority only. */
-  CALLBACK(write_bridge_ns, PERIODIC_EVENT_ROLE_BRIDGEAUTH),
+  CALLBACK(write_bridge_ns, PERIODIC_EVENT_ROLE_BRIDGEAUTH, 0),
+
   END_OF_PERIODIC_EVENTS
 };
 #undef CALLBACK
@@ -1548,6 +1559,12 @@ rescan_periodic_events(const or_options_t *options)
   for (int i = 0; periodic_events[i].name; ++i) {
     periodic_event_item_t *item = &periodic_events[i];
 
+    /* Handle the event flags. */
+    if (net_is_disabled() &&
+        (item->flags & PERIODIC_EVENT_FLAG_NEED_NET)) {
+      continue;
+    }
+
     /* Enable the event if needed. It is safe to enable an event that was
      * already enabled. Same goes for disabling it. */
     if (item->roles & roles) {

src/or/periodic.h

@@ -29,6 +29,15 @@
   (PERIODIC_EVENT_ROLE_AUTHORITIES | PERIODIC_EVENT_ROLE_CLIENT | \
    PERIODIC_EVENT_ROLE_HS_SERVICE | PERIODIC_EVENT_ROLE_ROUTER)
 
+/*
+ * Event flags which can change the behavior of an event.
+ */
+
+/* Indicate that the event needs the network meaning that if we are in
+ * DisableNetwork or hibernation mode, the event won't be enabled. This obey
+ * the net_is_disabled() check. */
+#define PERIODIC_EVENT_FLAG_NEED_NET  (1U << 0)
+
 /** Callback function for a periodic event to take action.  The return value
 * influences the next time the function will get called.  Return
 * PERIODIC_EVENT_NO_UPDATE to not update <b>last_action_time</b> and be polled
@@ -49,13 +58,15 @@ typedef struct periodic_event_item_t {
 
   /* Bitmask of roles define above for which this event applies. */
   uint32_t roles;
+  /* Bitmask of flags which can change the behavior of the event. */
+  uint32_t flags;
   /* Indicate that this event has been enabled that is scheduled. */
   unsigned int enabled : 1;
 } periodic_event_item_t;
 
 /** events will get their interval from first execution */
-#define PERIODIC_EVENT(fn, r) { fn##_callback, 0, NULL, #fn, r, 0 }
-#define END_OF_PERIODIC_EVENTS { NULL, 0, NULL, NULL, 0, 0 }
+#define PERIODIC_EVENT(fn, r, f) { fn##_callback, 0, NULL, #fn, r, f, 0 }
+#define END_OF_PERIODIC_EVENTS { NULL, 0, NULL, NULL, 0, 0, 0 }
 
 /* Return true iff the given event was setup before thus is enabled to be
  * scheduled. */

src/test/test_periodic_event.c

@@ -16,6 +16,7 @@
 
 #include "or.h"
 #include "config.h"
+#include "hibernate.h"
 #include "hs_service.h"
 #include "main.h"
 #include "periodic.h"
@@ -74,6 +75,9 @@ test_pe_launch(void *arg)
   (void) arg;
 
   hs_init();
+  /* We need to put tor in hibernation live state so the events requiring
+   * network gets enabled. */
+  consider_hibernation(time(NULL));
 
   /* Hack: We'll set a dumb fn() of each events so they don't get called when
    * dispatching them. We just want to test the state of the callbacks, not