src/core/or/orconn_event.c

   1 /* Copyright (c) 2007-2018, The Tor Project, Inc. */
   2 /* See LICENSE for licensing information */
   3
   4 /**
   5  * \file orconn_event.c
   6  * \brief Publish state change messages for OR connections
   7  *
   8  * Implements a basic publish-subscribe framework for messages about
   9  * the state of OR connections.  The publisher calls the subscriber
  10  * callback functions synchronously.
  11  *
  12  * Although the synchronous calls might not simplify the call graph,
  13  * this approach improves data isolation because the publisher doesn't
  14  * need knowledge about the internals of subscribing subsystems.  It
  15  * also avoids race conditions that might occur in asynchronous
  16  * frameworks.
  17  **/
  18
  19 #include "core/or/or.h"
  20 #include "lib/subsys/subsys.h"
  21
  22 #define ORCONN_EVENT_PRIVATE
  23 #include "core/or/orconn_event.h"
  24 #include "core/or/orconn_event_sys.h"
  25
  26 /** List of subscribers */
  27 static smartlist_t *orconn_event_rcvrs;
  28
  29 /** Initialize subscriber list */
  30 static int
  31 orconn_event_init(void)
  32 {
  33   orconn_event_rcvrs = smartlist_new();
  34   return 0;
  35 }
  36
  37 /** Free subscriber list */
  38 static void
  39 orconn_event_fini(void)
  40 {
  41   smartlist_free(orconn_event_rcvrs);
  42 }
  43
  44 /**
  45  * Subscribe to messages about OR connection events
  46  *
  47  * Register a callback function to receive messages about ORCONNs.
  48  * The publisher calls this function synchronously.
  49  **/
  50 void
  51 orconn_event_subscribe(orconn_event_rcvr_t fn)
  52 {
  53   tor_assert(fn);
  54   /* Don't duplicate subscriptions. */
  55   if (smartlist_contains(orconn_event_rcvrs, fn))
  56     return;
  57
  58   smartlist_add(orconn_event_rcvrs, fn);
  59 }
  60
  61 /**
  62  * Publish a message about OR connection events
  63  *
  64  * This calls the subscriber receiver function synchronously.
  65  **/
  66 void
  67 orconn_event_publish(const orconn_event_msg_t *msg)
  68 {
  69   SMARTLIST_FOREACH_BEGIN(orconn_event_rcvrs, orconn_event_rcvr_t, fn) {
  70     tor_assert(fn);
  71     (*fn)(msg);
  72   } SMARTLIST_FOREACH_END(fn);
  73 }
  74
  75 const subsys_fns_t sys_orconn_event = {
  76   .name = "orconn_event",
  77   .supported = true,
  78   .level = -33,
  79   .initialize = orconn_event_init,
  80   .shutdown = orconn_event_fini,
  81 };