Data Structures | Macros | Functions | Variables
timers.c File Reference

Wrapper around William Ahern's fast hierarchical timer wheel implementation, to tie it in with a libevent backend. More...

#include "orconfig.h"
#include "lib/evloop/compat_libevent.h"
#include "lib/evloop/timers.h"
#include "lib/intmath/muldiv.h"
#include "lib/log/log.h"
#include "lib/log/util_bug.h"
#include "lib/malloc/malloc.h"
#include "lib/time/compat_time.h"
#include "ext/timeouts/timeout.c"

Go to the source code of this file.

Data Structures

struct  timeout_cb_t


#define TIMEOUT_PUBLIC   static
#define WHEEL_NUM   5
#define USEC_PER_TICK   100
#define USEC_PER_SEC   1000000
#define MIN_CHECK_SECONDS   3600
#define MIN_CHECK_TICKS    (((timeout_t)MIN_CHECK_SECONDS) * (1000000 / USEC_PER_TICK))


static timeout_t tv_to_timeout (const struct timeval *tv)
static void timeout_to_tv (timeout_t t, struct timeval *tv_out)
static void timer_advance_to_cur_time (const monotime_t *now)
static void libevent_timer_reschedule (void)
STATIC void timers_run_pending (void)
static void libevent_timer_callback (mainloop_event_t *ev, void *arg)
void timers_initialize (void)
void timers_shutdown (void)
tor_timer_t * timer_new (timer_cb_fn_t cb, void *arg)
void timer_free_ (tor_timer_t *t)
void timer_set_cb (tor_timer_t *t, timer_cb_fn_t cb, void *arg)
void timer_get_cb (const tor_timer_t *t, timer_cb_fn_t *cb_out, void **arg_out)
void timer_schedule (tor_timer_t *t, const struct timeval *tv)
void timer_disable (tor_timer_t *t)


static struct timeoutsglobal_timeouts = NULL
static struct mainloop_event_tglobal_timer_event = NULL
static monotime_t start_of_time

Detailed Description

Wrapper around William Ahern's fast hierarchical timer wheel implementation, to tie it in with a libevent backend.

Only use these functions from the main thread.

The main advantage of tor_timer_t over using libevent's timers is that they're way more efficient if we need to have thousands or millions of them. For more information, see

Periodic timers are available in the backend, but I've turned them off. We can turn them back on if needed.

Definition in file timers.c.

Macro Definition Documentation


#define MIN_CHECK_SECONDS   3600

Check at least once every N seconds.

Definition at line 107 of file timers.c.


#define MIN_CHECK_TICKS    (((timeout_t)MIN_CHECK_SECONDS) * (1000000 / USEC_PER_TICK))

Check at least once every N ticks.

Definition at line 110 of file timers.c.


#define USEC_PER_SEC   1000000

One million microseconds in a second

Definition at line 104 of file timers.c.


#define USEC_PER_TICK   100

We need to choose this value carefully. Because we're using timer wheels, it actually costs us to have extra resolution we don't use. So for now, I'm going to define our resolution as .1 msec, and hope that's good enough.

Note that two of the most popular libevent backends (epoll without timerfd, and windows select), simply can't support sub-millisecond resolution, do this is optimistic for a lot of users.

Definition at line 101 of file timers.c.

Function Documentation

◆ libevent_timer_callback()

static void libevent_timer_callback ( mainloop_event_t ev,
void *  arg 

Invoked when the libevent timer has expired: see which tor_timer_t events have fired, activate their callbacks, and reschedule the libevent timer.

Definition at line 190 of file timers.c.

◆ libevent_timer_reschedule()

static void libevent_timer_reschedule ( void  )

Adjust the time at which the libevent timer should fire based on the next-expiring time in global_timeouts

Definition at line 155 of file timers.c.

Referenced by libevent_timer_callback().

◆ timeout_to_tv()

static void timeout_to_tv ( timeout_t  t,
struct timeval tv_out 

Convert the timeout in t to a timeval in tv_out. Only use this for delays, not absolute times.

Definition at line 132 of file timers.c.

◆ timer_advance_to_cur_time()

static void timer_advance_to_cur_time ( const monotime_t now)

Update the timer tv to the current time in tv.

Definition at line 143 of file timers.c.

Referenced by libevent_timer_reschedule(), and timers_run_pending().

◆ timer_disable()

void timer_disable ( tor_timer_t *  t)

Cancel the timer t if it is currently scheduled. (It's okay to call this on an unscheduled timer.

Definition at line 326 of file timers.c.

◆ timer_free_()

void timer_free_ ( tor_timer_t *  t)

Release all storage held by t, and unschedule it if was already scheduled.

Definition at line 263 of file timers.c.

◆ timer_get_cb()

void timer_get_cb ( const tor_timer_t *  t,
timer_cb_fn_t *  cb_out,
void **  arg_out 

Set *cb_out (if provided) to this timer's callback function, and *arg_out (if provided) to this timer's callback argument.

Definition at line 287 of file timers.c.

◆ timer_new()

tor_timer_t* timer_new ( timer_cb_fn_t  cb,
void *  arg 

Allocate and return a new timer, with given callback and argument.

Definition at line 250 of file timers.c.

◆ timer_schedule()

void timer_schedule ( tor_timer_t *  t,
const struct timeval tv 

Schedule the timer t to fire at the current time plus a delay of delay microseconds. All times are relative to monotime_get().

Definition at line 301 of file timers.c.

◆ timer_set_cb()

void timer_set_cb ( tor_timer_t *  t,
timer_cb_fn_t  cb,
void *  arg 

Change the callback and argument associated with a timer t.

Definition at line 276 of file timers.c.

◆ timers_initialize()

void timers_initialize ( void  )

Initialize the timers subsystem. Requires that libevent has already been initialized.

Definition at line 205 of file timers.c.

◆ timers_run_pending()

STATIC void timers_run_pending ( void  )

Run the callback of every timer that has expired, based on the current output of monotime_get().

Definition at line 173 of file timers.c.

Referenced by libevent_timer_callback().

◆ timers_shutdown()

void timers_shutdown ( void  )

Release all storage held in the timers subsystem. Does not fire timers.

Definition at line 234 of file timers.c.

Referenced by tor_cleanup().

◆ tv_to_timeout()

static timeout_t tv_to_timeout ( const struct timeval tv)

Convert the timeval in tv to a timeout_t, and return it.

The output resolution is set by USEC_PER_TICK. Only use this to convert delays to number of ticks; the time represented by 0 is undefined.

Definition at line 120 of file timers.c.