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// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/viz/common/frame_sinks/delay_based_time_source.h"
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <string>
#include "base/check_op.h"
#include "base/functional/bind.h"
#include "base/location.h"
#include "base/task/single_thread_task_runner.h"
#include "base/time/time.h"
#include "base/trace_event/trace_event.h"
#include "base/trace_event/traced_value.h"
#include "components/viz/common/features.h"
#include "components/viz/common/frame_sinks/begin_frame_args.h"
namespace viz {
// The following methods correspond to the DelayBasedTimeSource that uses
// the base::TimeTicks::Now as the timebase.
DelayBasedTimeSource::DelayBasedTimeSource(
base::SingleThreadTaskRunner* task_runner)
: client_(nullptr),
active_(false),
timebase_(base::TimeTicks()),
interval_(BeginFrameArgs::DefaultInterval()),
last_tick_time_(base::TimeTicks() - interval_),
task_runner_(task_runner),
tick_closure_(base::BindRepeating(&DelayBasedTimeSource::OnTimerTick,
base::Unretained(this))) {}
DelayBasedTimeSource::~DelayBasedTimeSource() = default;
void DelayBasedTimeSource::SetActive(bool active) {
TRACE_EVENT1("viz", "DelayBasedTimeSource::SetActive", "active", active);
if (active == active_)
return;
active_ = active;
if (active_) {
timer_.SetTaskRunner(task_runner_.get());
PostNextTickTask(Now());
} else {
timer_.Stop();
last_tick_time_ = base::TimeTicks();
next_tick_time_ = base::TimeTicks();
}
}
base::TimeDelta DelayBasedTimeSource::Interval() const {
return interval_;
}
bool DelayBasedTimeSource::Active() const {
return active_;
}
base::TimeTicks DelayBasedTimeSource::LastTickTime() const {
return last_tick_time_;
}
base::TimeTicks DelayBasedTimeSource::NextTickTime() const {
return next_tick_time_;
}
void DelayBasedTimeSource::OnTimerTick() {
DCHECK(active_);
last_tick_time_ = next_tick_time_;
PostNextTickTask(Now());
// Fire the tick.
if (client_)
client_->OnTimerTick();
}
void DelayBasedTimeSource::SetClient(DelayBasedTimeSourceClient* client) {
client_ = client;
}
void DelayBasedTimeSource::SetTimebaseAndInterval(base::TimeTicks timebase,
base::TimeDelta interval) {
interval_ = interval;
timebase_ = timebase;
}
base::TimeTicks DelayBasedTimeSource::Now() const {
return base::TimeTicks::Now();
}
// This code tries to achieve an average tick rate as close to interval_ as
// possible. To do this, it has to deal with a few basic issues:
// 1. PostDelayedTask can delay only at a millisecond granularity. So, 16.666
// has to posted as 16 or 17.
// 2. A delayed task may come back a bit late (a few ms), or really late
// (frames later)
//
// The basic idea with this scheduler here is to keep track of where we *want*
// to run in tick_target_. We update this with the exact interval.
//
// Then, when we post our task, we take the floor of (tick_target_ and Now()).
// If we started at now=0, and 60FPs (all times in milliseconds):
// now=0 target=16.667 PostDelayedTask(16)
//
// When our callback runs, we figure out how far off we were from that goal.
// Because of the flooring operation, and assuming our timer runs exactly when
// it should, this yields:
// now=16 target=16.667
//
// Since we can't post a 0.667 ms task to get to now=16, we just treat this as a
// tick. Then, we update target to be 33.333. We now post another task based on
// the difference between our target and now:
// now=16 tick_target=16.667 new_target=33.333 -->
// PostDelayedTask(floor(33.333 - 16)) --> PostDelayedTask(17)
//
// Over time, with no late tasks, this leads to us posting tasks like this:
// now=0 tick_target=0 new_target=16.667 -->
// tick(), PostDelayedTask(16)
// now=16 tick_target=16.667 new_target=33.333 -->
// tick(), PostDelayedTask(17)
// now=33 tick_target=33.333 new_target=50.000 -->
// tick(), PostDelayedTask(17)
// now=50 tick_target=50.000 new_target=66.667 -->
// tick(), PostDelayedTask(16)
//
// We treat delays in tasks differently depending on the amount of delay we
// encounter. Suppose we posted a task with a target=16.667:
// Case 1: late but not unrecoverably-so
// now=18 tick_target=16.667
//
// Case 2: so late we obviously missed the tick
// now=25.0 tick_target=16.667
//
// We treat the first case as a tick anyway, and assume the delay was unusual.
// Thus, we compute the new_target based on the old timebase:
// now=18 tick_target=16.667 new_target=33.333 -->
// tick(), PostDelayedTask(floor(33.333-18)) --> PostDelayedTask(15)
// This brings us back to 18+15 = 33, which was where we would have been if the
// task hadn't been late.
//
// For the really late delay, we we move to the next logical tick. The timebase
// is not reset.
// now=37 tick_target=16.667 new_target=50.000 -->
// tick(), PostDelayedTask(floor(50.000-37)) --> PostDelayedTask(13)
void DelayBasedTimeSource::PostNextTickTask(base::TimeTicks now) {
if (interval_.is_zero()) {
next_tick_time_ = now;
timer_.Start(FROM_HERE, base::TimeTicks(), tick_closure_,
base::subtle::DelayPolicy::kPrecise);
} else {
next_tick_time_ = now.SnappedToNextTick(timebase_, interval_);
// TODO( crbug.com/398090404 ): Remove the code in this condition as it is
// being superseded by the next block.
if (next_tick_time_ == now) {
next_tick_time_ += interval_;
}
if (base::FeatureList::IsEnabled(
features::kAvoidDuplicateDelayBeginFrame)) {
// Some devices report vblank timings with enough variance as to confuse
// 'SnappedToNextTick' on the time remaining for next begin frame. This
// code allows for up to 'kMaxJudderAllowed' time for these values to
// simply be corrected to the next interval and thereby avoid an erroneous
// double tick. See crbug.com/398090404 for details.
const auto kMaxJudderAllowed = base::Microseconds(500);
if (now + kMaxJudderAllowed >= next_tick_time_) {
next_tick_time_ += interval_;
}
}
DCHECK_GT(next_tick_time_, now);
timer_.Start(FROM_HERE, next_tick_time_, tick_closure_,
base::subtle::DelayPolicy::kPrecise);
}
}
std::string DelayBasedTimeSource::TypeString() const {
return "DelayBasedTimeSource";
}
void DelayBasedTimeSource::AsValueInto(
base::trace_event::TracedValue* state) const {
state->SetString("type", TypeString());
state->SetDouble("last_tick_time_us",
LastTickTime().since_origin().InMicrosecondsF());
state->SetDouble("next_tick_time_us",
NextTickTime().since_origin().InMicrosecondsF());
state->SetDouble("interval_us", interval_.InMicrosecondsF());
state->SetDouble("timebase_us", timebase_.since_origin().InMicrosecondsF());
state->SetBoolean("active", active_);
}
} // namespace viz
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