diff options
Diffstat (limited to 'src/common')
| -rw-r--r-- | src/common/compat_libevent.c | 115 | ||||
| -rw-r--r-- | src/common/compat_libevent.h | 3 |
2 files changed, 110 insertions, 8 deletions
diff --git a/src/common/compat_libevent.c b/src/common/compat_libevent.c index 0d0e4337bb..9936c0aac4 100644 --- a/src/common/compat_libevent.c +++ b/src/common/compat_libevent.c @@ -79,6 +79,43 @@ tor_event_free_(struct event *ev) /** Global event base for use by the main thread. */ static struct event_base *the_event_base = NULL; +/** + * @defgroup postloop post-loop event helpers + * + * If we're not careful, Libevent can susceptible to infinite event chains: + * one event can activate another, whose callback activates another, whose + * callback activates another, ad infinitum. While this is happening, + * Libevent won't be checking timeouts, socket-based events, signals, and so + * on. + * + * We solve this problem by marking some events as "post-loop". A post-loop + * event behaves like any ordinary event, but any events that _it_ activates + * cannot run until Libevent has checked for other events at least once. + * + * @{ */ + +/** + * An event that stops Libevent from running any more events on the current + * iteration of its loop, until it has re-checked for socket events, signal + * events, timeouts, etc. + */ +static struct event *rescan_mainloop_ev = NULL; + +/** + * Callback to implement rescan_mainloop_ev: it simply exits the mainloop, + * and relies on Tor to re-enter the mainloop since no error has occurred. + */ +static void +rescan_mainloop_cb(evutil_socket_t fd, short events, void *arg) +{ + (void)fd; + (void)events; + struct event_base *the_base = arg; + event_base_loopbreak(the_base); +} + +/** @} */ + /* This is what passes for version detection on OSX. We set * MACOSX_KQUEUE_IS_BROKEN to true iff we're on a version of OSX before * 10.4.0 (aka 1040). */ @@ -130,6 +167,15 @@ tor_libevent_initialize(tor_libevent_cfg *torcfg) /* LCOV_EXCL_STOP */ } + rescan_mainloop_ev = event_new(the_event_base, -1, 0, + rescan_mainloop_cb, the_event_base); + if (!rescan_mainloop_ev) { + /* LCOV_EXCL_START */ + log_err(LD_GENERAL, "Unable to create rescan event: cannot continue."); + exit(1); // exit ok: libevent is broken. + /* LCOV_EXCL_STOP */ + } + log_info(LD_GENERAL, "Initialized libevent version %s using method %s. Good.", event_get_version(), tor_libevent_get_method()); @@ -251,6 +297,52 @@ mainloop_event_cb(evutil_socket_t fd, short what, void *arg) } /** + * As mainloop_event_cb, but implements a post-loop event. + */ +static void +mainloop_event_postloop_cb(evutil_socket_t fd, short what, void *arg) +{ + (void)fd; + (void)what; + + /* Note that if rescan_mainloop_ev is already activated, + * event_active() will do nothing: only the first post-loop event that + * happens each time through the event loop will cause it to be + * activated. + * + * Because event_active() puts events on a FIFO queue, every event + * that is made active _after_ rescan_mainloop_ev will get its + * callback run after rescan_mainloop_cb is called -- that is, on the + * next iteration of the loop. + */ + event_active(rescan_mainloop_ev, EV_READ, 1); + + mainloop_event_t *mev = arg; + mev->cb(mev, mev->userdata); +} + +/** + * Helper for mainloop_event_new() and mainloop_event_postloop_new(). + */ +static mainloop_event_t * +mainloop_event_new_impl(int postloop, + void (*cb)(mainloop_event_t *, void *), + void *userdata) +{ + tor_assert(cb); + + struct event_base *base = tor_libevent_get_base(); + mainloop_event_t *mev = tor_malloc_zero(sizeof(mainloop_event_t)); + mev->ev = tor_event_new(base, -1, 0, + postloop ? mainloop_event_postloop_cb : mainloop_event_cb, + mev); + tor_assert(mev->ev); + mev->cb = cb; + mev->userdata = userdata; + return mev; +} + +/** * Create and return a new mainloop_event_t to run the function <b>cb</b>. * * When run, the callback function will be passed the mainloop_event_t @@ -265,15 +357,21 @@ mainloop_event_t * mainloop_event_new(void (*cb)(mainloop_event_t *, void *), void *userdata) { - tor_assert(cb); + return mainloop_event_new_impl(0, cb, userdata); +} - struct event_base *base = tor_libevent_get_base(); - mainloop_event_t *mev = tor_malloc_zero(sizeof(mainloop_event_t)); - mev->ev = tor_event_new(base, -1, 0, mainloop_event_cb, mev); - tor_assert(mev->ev); - mev->cb = cb; - mev->userdata = userdata; - return mev; +/** + * As mainloop_event_new(), but create a post-loop event. + * + * A post-loop event behaves like any ordinary event, but any events + * that _it_ activates cannot run until Libevent has checked for other + * events at least once. + */ +mainloop_event_t * +mainloop_event_postloop_new(void (*cb)(mainloop_event_t *, void *), + void *userdata) +{ + return mainloop_event_new_impl(1, cb, userdata); } /** @@ -358,6 +456,7 @@ tor_init_libevent_rng(void) void tor_libevent_free_all(void) { + tor_event_free(rescan_mainloop_ev); if (the_event_base) event_base_free(the_event_base); the_event_base = NULL; diff --git a/src/common/compat_libevent.h b/src/common/compat_libevent.h index c8b0371564..29c6ad375a 100644 --- a/src/common/compat_libevent.h +++ b/src/common/compat_libevent.h @@ -37,6 +37,9 @@ void periodic_timer_free_(periodic_timer_t *); typedef struct mainloop_event_t mainloop_event_t; mainloop_event_t *mainloop_event_new(void (*cb)(mainloop_event_t *, void *), void *userdata); +mainloop_event_t * mainloop_event_postloop_new( + void (*cb)(mainloop_event_t *, void *), + void *userdata); void mainloop_event_activate(mainloop_event_t *event); int mainloop_event_schedule(mainloop_event_t *event, const struct timeval *delay); |