/**
* gst_clock_add_observation:
* @clock: a #GstClock
* @slave: a time on the slave
* @master: a time on the master
* @r_squared: (out): a pointer to hold the result
*
* The time @master of the master clock and the time @slave of the slave
* clock are added to the list of observations. If enough observations
* are available, a linear regression algorithm is run on the
* observations and @clock is recalibrated.
*
* If this functions returns %TRUE, @r_squared will contain the
* correlation coefficient of the interpolation. A value of 1.0
* means a perfect regression was performed. This value can
* be used to control the sampling frequency of the master and slave
* clocks.
*
* Returns: %TRUE if enough observations were added to run the
* regression algorithm.
*
* MT safe.
*/
gboolean
gst_clock_add_observation (GstClock * clock, GstClockTime slave,
GstClockTime master, gdouble * r_squared)
{
GstClockTime m_num, m_denom, b, xbase;
if (!gst_clock_add_observation_unapplied (clock, slave, master, r_squared,
&xbase, &b, &m_num, &m_denom))
return FALSE;
/* if we have a valid regression, adjust the clock */
gst_clock_set_calibration (clock, xbase, b, m_num, m_denom);
return TRUE;
}
static void
gst_net_client_internal_clock_observe_times (GstNetClientInternalClock * self,
GstClockTime local_1, GstClockTime remote_1, GstClockTime remote_2,
GstClockTime local_2)
{
GstClockTime current_timeout = 0;
GstClockTime local_avg, remote_avg;
gdouble r_squared;
GstClock *clock;
GstClockTime rtt, rtt_limit, min_update_interval;
/* Use for discont tracking */
GstClockTime time_before = 0;
GstClockTime min_guess = 0;
GstClockTimeDiff time_discont = 0;
gboolean synched, now_synched;
GstClockTime internal_time, external_time, rate_num, rate_den;
GstClockTime orig_internal_time, orig_external_time, orig_rate_num,
orig_rate_den;
GstClockTime max_discont;
GstClockTime last_rtts[MEDIAN_PRE_FILTERING_WINDOW];
GstClockTime median;
gint i;
GST_OBJECT_LOCK (self);
rtt_limit = self->roundtrip_limit;
GST_LOG_OBJECT (self,
"local1 %" G_GUINT64_FORMAT " remote1 %" G_GUINT64_FORMAT " remote2 %"
G_GUINT64_FORMAT " local2 %" G_GUINT64_FORMAT, local_1, remote_1,
remote_2, local_2);
/* If the server told us a poll interval and it's bigger than the
* one configured via the property, use the server's */
if (self->last_remote_poll_interval != GST_CLOCK_TIME_NONE &&
self->last_remote_poll_interval > self->minimum_update_interval)
min_update_interval = self->last_remote_poll_interval;
else
min_update_interval = self->minimum_update_interval;
GST_OBJECT_UNLOCK (self);
if (local_2 < local_1) {
GST_LOG_OBJECT (self, "Dropping observation: receive time %" GST_TIME_FORMAT
" < send time %" GST_TIME_FORMAT, GST_TIME_ARGS (local_1),
GST_TIME_ARGS (local_2));
goto bogus_observation;
}
if (remote_2 < remote_1) {
GST_LOG_OBJECT (self,
"Dropping observation: remote receive time %" GST_TIME_FORMAT
" < send time %" GST_TIME_FORMAT, GST_TIME_ARGS (remote_1),
GST_TIME_ARGS (remote_2));
goto bogus_observation;
}
/* The round trip time is (assuming symmetric path delays)
* delta = (local_2 - local_1) - (remote_2 - remote_1)
*/
rtt = GST_CLOCK_DIFF (local_1, local_2) - GST_CLOCK_DIFF (remote_1, remote_2);
if ((rtt_limit > 0) && (rtt > rtt_limit)) {
GST_LOG_OBJECT (self,
"Dropping observation: RTT %" GST_TIME_FORMAT " > limit %"
GST_TIME_FORMAT, GST_TIME_ARGS (rtt), GST_TIME_ARGS (rtt_limit));
goto bogus_observation;
}
for (i = 1; i < MEDIAN_PRE_FILTERING_WINDOW; i++)
self->last_rtts[i - 1] = self->last_rtts[i];
self->last_rtts[i - 1] = rtt;
if (self->last_rtts_missing) {
self->last_rtts_missing--;
} else {
memcpy (&last_rtts, &self->last_rtts, sizeof (last_rtts));
g_qsort_with_data (&last_rtts,
MEDIAN_PRE_FILTERING_WINDOW, sizeof (GstClockTime),
(GCompareDataFunc) compare_clock_time, NULL);
median = last_rtts[MEDIAN_PRE_FILTERING_WINDOW / 2];
/* FIXME: We might want to use something else here, like only allowing
* things in the interquartile range, or also filtering away delays that
* are too small compared to the median. This here worked well enough
* in tests so far.
*/
if (rtt > 2 * median) {
GST_LOG_OBJECT (self,
"Dropping observation, long RTT %" GST_TIME_FORMAT " > 2 * median %"
GST_TIME_FORMAT, GST_TIME_ARGS (rtt), GST_TIME_ARGS (median));
goto bogus_observation;
}
}
/* Track an average round trip time, for a bit of smoothing */
/* Always update before discarding a sample, so genuine changes in
* the network get picked up, eventually */
if (self->rtt_avg == GST_CLOCK_TIME_NONE)
self->rtt_avg = rtt;
else if (rtt < self->rtt_avg) /* Shorter RTTs carry more weight than longer */
self->rtt_avg = (3 * self->rtt_avg + rtt) / 4;
else
self->rtt_avg = (15 * self->rtt_avg + rtt) / 16;
if (rtt > 2 * self->rtt_avg) {
GST_LOG_OBJECT (self,
"Dropping observation, long RTT %" GST_TIME_FORMAT " > 2 * avg %"
GST_TIME_FORMAT, GST_TIME_ARGS (rtt), GST_TIME_ARGS (self->rtt_avg));
goto bogus_observation;
}
/* The difference between the local and remote clock (again assuming
* symmetric path delays):
*
* local_1 + delta / 2 - remote_1 = theta
* or
* local_2 - delta / 2 - remote_2 = theta
*
* which gives after some simple algebraic transformations:
*
* (remote_1 - local_1) + (remote_2 - local_2)
* theta = -------------------------------------------
* 2
*
*
* Thus remote time at local_avg is equal to:
*
* local_avg + theta =
*
* local_1 + local_2 (remote_1 - local_1) + (remote_2 - local_2)
* ----------------- + -------------------------------------------
* 2 2
*
* =
*
* remote_1 + remote_2
* ------------------- = remote_avg
* 2
*
* We use this for our clock estimation, i.e. local_avg at remote clock
* being the same as remote_avg.
*/
local_avg = (local_2 + local_1) / 2;
remote_avg = (remote_2 + remote_1) / 2;
GST_LOG_OBJECT (self,
"remoteavg %" G_GUINT64_FORMAT " localavg %" G_GUINT64_FORMAT,
remote_avg, local_avg);
clock = GST_CLOCK_CAST (self);
/* Store what the clock produced as 'now' before this update */
gst_clock_get_calibration (GST_CLOCK_CAST (self), &orig_internal_time,
&orig_external_time, &orig_rate_num, &orig_rate_den);
internal_time = orig_internal_time;
external_time = orig_external_time;
rate_num = orig_rate_num;
rate_den = orig_rate_den;
min_guess =
gst_clock_adjust_with_calibration (GST_CLOCK_CAST (self), local_1,
internal_time, external_time, rate_num, rate_den);
time_before =
gst_clock_adjust_with_calibration (GST_CLOCK_CAST (self), local_2,
internal_time, external_time, rate_num, rate_den);
/* Maximum discontinuity, when we're synched with the master. Could make this a property,
* but this value seems to work fine */
max_discont = self->rtt_avg / 4;
/* If the remote observation was within a max_discont window around our min/max estimates, we're synched */
synched =
(GST_CLOCK_DIFF (remote_avg, min_guess) < (GstClockTimeDiff) (max_discont)
&& GST_CLOCK_DIFF (time_before,
remote_avg) < (GstClockTimeDiff) (max_discont));
if (gst_clock_add_observation_unapplied (GST_CLOCK_CAST (self),
local_avg, remote_avg, &r_squared, &internal_time, &external_time,
&rate_num, &rate_den)) {
/* Now compare the difference (discont) in the clock
* after this observation */
time_discont = GST_CLOCK_DIFF (time_before,
gst_clock_adjust_with_calibration (GST_CLOCK_CAST (self), local_2,
internal_time, external_time, rate_num, rate_den));
/* If we were in sync with the remote clock, clamp the allowed
* discontinuity to within quarter of one RTT. In sync means our send/receive estimates
* of remote time correctly windowed the actual remote time observation */
if (synched && ABS (time_discont) > max_discont) {
GstClockTimeDiff offset;
GST_DEBUG_OBJECT (clock,
"Too large a discont, clamping to 1/4 average RTT = %"
GST_TIME_FORMAT, GST_TIME_ARGS (max_discont));
if (time_discont > 0) { /* Too large a forward step - add a -ve offset */
offset = max_discont - time_discont;
if (-offset > external_time)
external_time = 0;
else
external_time += offset;
} else { /* Too large a backward step - add a +ve offset */
offset = -(max_discont + time_discont);
external_time += offset;
}
time_discont += offset;
}
/* Check if the new clock params would have made our observation within range */
now_synched =
(GST_CLOCK_DIFF (remote_avg,
gst_clock_adjust_with_calibration (GST_CLOCK_CAST (self),
local_1, internal_time, external_time, rate_num,
rate_den)) < (GstClockTimeDiff) (max_discont))
&&
(GST_CLOCK_DIFF (gst_clock_adjust_with_calibration
(GST_CLOCK_CAST (self), local_2, internal_time, external_time,
rate_num, rate_den),
remote_avg) < (GstClockTimeDiff) (max_discont));
/* Only update the clock if we had synch or just gained it */
if (synched || now_synched || self->skipped_updates > MAX_SKIPPED_UPDATES) {
gst_clock_set_calibration (GST_CLOCK_CAST (self), internal_time,
external_time, rate_num, rate_den);
/* ghetto formula - shorter timeout for bad correlations */
current_timeout = (1e-3 / (1 - MIN (r_squared, 0.99999))) * GST_SECOND;
current_timeout =
MIN (current_timeout, gst_clock_get_timeout (GST_CLOCK_CAST (self)));
self->skipped_updates = 0;
/* FIXME: When do we consider the clock absolutely not synced anymore? */
gst_clock_set_synced (GST_CLOCK (self), TRUE);
} else {
/* Restore original calibration vars for the report, we're not changing the clock */
internal_time = orig_internal_time;
external_time = orig_external_time;
rate_num = orig_rate_num;
rate_den = orig_rate_den;
time_discont = 0;
self->skipped_updates++;
}
}
/* Limit the polling to at most one per minimum_update_interval */
if (rtt < min_update_interval)
current_timeout = MAX (min_update_interval - rtt, current_timeout);
GST_OBJECT_LOCK (self);
if (self->busses) {
GstStructure *s;
GstMessage *msg;
GList *l;
/* Output a stats message, whether we updated the clock or not */
s = gst_structure_new ("gst-netclock-statistics",
"synchronised", G_TYPE_BOOLEAN, synched,
"rtt", G_TYPE_UINT64, rtt,
"rtt-average", G_TYPE_UINT64, self->rtt_avg,
"local", G_TYPE_UINT64, local_avg,
"remote", G_TYPE_UINT64, remote_avg,
"discontinuity", G_TYPE_INT64, time_discont,
"remote-min-estimate", G_TYPE_UINT64, min_guess,
"remote-max-estimate", G_TYPE_UINT64, time_before,
"remote-min-error", G_TYPE_INT64, GST_CLOCK_DIFF (remote_avg,
min_guess), "remote-max-error", G_TYPE_INT64,
GST_CLOCK_DIFF (remote_avg, time_before), "request-send", G_TYPE_UINT64,
local_1, "request-receive", G_TYPE_UINT64, local_2, "r-squared",
G_TYPE_DOUBLE, r_squared, "timeout", G_TYPE_UINT64, current_timeout,
"internal-time", G_TYPE_UINT64, internal_time, "external-time",
G_TYPE_UINT64, external_time, "rate-num", G_TYPE_UINT64, rate_num,
"rate-den", G_TYPE_UINT64, rate_den, "rate", G_TYPE_DOUBLE,
(gdouble) (rate_num) / rate_den, "local-clock-offset", G_TYPE_INT64,
GST_CLOCK_DIFF (internal_time, external_time), NULL);
msg = gst_message_new_element (GST_OBJECT (self), s);
for (l = self->busses; l; l = l->next)
gst_bus_post (l->data, gst_message_ref (msg));
gst_message_unref (msg);
}
GST_OBJECT_UNLOCK (self);
GST_INFO ("next timeout: %" GST_TIME_FORMAT, GST_TIME_ARGS (current_timeout));
self->timeout_expiration = gst_util_get_timestamp () + current_timeout;
return;
bogus_observation:
/* Schedule a new packet again soon */
self->timeout_expiration = gst_util_get_timestamp () + (GST_SECOND / 4);
return;
}
