Revert "Delete CC."

cc/scheduler/delay_based_time_source.cc

+// Copyright 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "cc/scheduler/delay_based_time_source.h"
+
+#include <algorithm>
+#include <cmath>
+#include <string>
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/single_thread_task_runner.h"
+#include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_argument.h"
+
+namespace cc {
+
+namespace {
+
+// kDoubleTickDivisor prevents ticks from running within the specified
+// fraction of an interval.  This helps account for jitter in the timebase as
+// well as quick timer reactivation.
+static const int kDoubleTickDivisor = 2;
+
+// kIntervalChangeThreshold is the fraction of the interval that will trigger an
+// immediate interval change.  kPhaseChangeThreshold is the fraction of the
+// interval that will trigger an immediate phase change.  If the changes are
+// within the thresholds, the change will take place on the next tick.  If
+// either change is outside the thresholds, the next tick will be canceled and
+// reissued immediately.
+static const double kIntervalChangeThreshold = 0.25;
+static const double kPhaseChangeThreshold = 0.25;
+
+}  // namespace
+
+// The following methods correspond to the DelayBasedTimeSource that uses
+// the base::TimeTicks::Now as the timebase.
+scoped_refptr<DelayBasedTimeSourceHighRes> DelayBasedTimeSourceHighRes::Create(
+    base::TimeDelta interval,
+    base::SingleThreadTaskRunner* task_runner) {
+  return make_scoped_refptr(
+      new DelayBasedTimeSourceHighRes(interval, task_runner));
+}
+
+DelayBasedTimeSourceHighRes::DelayBasedTimeSourceHighRes(
+    base::TimeDelta interval,
+    base::SingleThreadTaskRunner* task_runner)
+    : DelayBasedTimeSource(interval, task_runner) {
+}
+
+DelayBasedTimeSourceHighRes::~DelayBasedTimeSourceHighRes() {}
+
+base::TimeTicks DelayBasedTimeSourceHighRes::Now() const {
+  return base::TimeTicks::Now();
+}
+
+// The following methods correspond to the DelayBasedTimeSource that uses
+// the base::TimeTicks::Now as the timebase.
+scoped_refptr<DelayBasedTimeSource> DelayBasedTimeSource::Create(
+    base::TimeDelta interval,
+    base::SingleThreadTaskRunner* task_runner) {
+  return make_scoped_refptr(new DelayBasedTimeSource(interval, task_runner));
+}
+
+DelayBasedTimeSource::DelayBasedTimeSource(
+    base::TimeDelta interval,
+    base::SingleThreadTaskRunner* task_runner)
+    : client_(NULL),
+      last_tick_time_(base::TimeTicks() - interval),
+      current_parameters_(interval, base::TimeTicks()),
+      next_parameters_(interval, base::TimeTicks()),
+      active_(false),
+      task_runner_(task_runner),
+      weak_factory_(this) {
+  DCHECK_GT(interval.ToInternalValue(), 0);
+}
+
+DelayBasedTimeSource::~DelayBasedTimeSource() {}
+
+base::TimeTicks DelayBasedTimeSource::SetActive(bool active) {
+  TRACE_EVENT1("cc", "DelayBasedTimeSource::SetActive", "active", active);
+  if (active == active_)
+    return base::TimeTicks();
+  active_ = active;
+
+  if (!active_) {
+    weak_factory_.InvalidateWeakPtrs();
+    return base::TimeTicks();
+  }
+
+  PostNextTickTask(Now());
+
+  // Determine if there was a tick that was missed while not active.
+  base::TimeTicks last_tick_time_if_always_active =
+    current_parameters_.tick_target - current_parameters_.interval;
+  base::TimeTicks new_tick_time_threshold =
+    last_tick_time_ + current_parameters_.interval / kDoubleTickDivisor;
+  if (last_tick_time_if_always_active >  new_tick_time_threshold) {
+    last_tick_time_ = last_tick_time_if_always_active;
+    return last_tick_time_;
+  }
+
+  return base::TimeTicks();
+}
+
+bool DelayBasedTimeSource::Active() const { return active_; }
+
+base::TimeTicks DelayBasedTimeSource::LastTickTime() const {
+  return last_tick_time_;
+}
+
+base::TimeTicks DelayBasedTimeSource::NextTickTime() const {
+  return Active() ? current_parameters_.tick_target : base::TimeTicks();
+}
+
+void DelayBasedTimeSource::OnTimerFired() {
+  DCHECK(active_);
+
+  last_tick_time_ = current_parameters_.tick_target;
+
+  PostNextTickTask(Now());
+
+  // Fire the tick.
+  if (client_)
+    client_->OnTimerTick();
+}
+
+void DelayBasedTimeSource::SetClient(TimeSourceClient* client) {
+  client_ = client;
+}
+
+void DelayBasedTimeSource::SetTimebaseAndInterval(base::TimeTicks timebase,
+                                                  base::TimeDelta interval) {
+  DCHECK_GT(interval.ToInternalValue(), 0);
+  next_parameters_.interval = interval;
+  next_parameters_.tick_target = timebase;
+
+  if (!active_) {
+    // If we aren't active, there's no need to reset the timer.
+    return;
+  }
+
+  // If the change in interval is larger than the change threshold,
+  // request an immediate reset.
+  double interval_delta =
+      std::abs((interval - current_parameters_.interval).InSecondsF());
+  double interval_change = interval_delta / interval.InSecondsF();
+  if (interval_change > kIntervalChangeThreshold) {
+    TRACE_EVENT_INSTANT0("cc", "DelayBasedTimeSource::IntervalChanged",
+                         TRACE_EVENT_SCOPE_THREAD);
+    SetActive(false);
+    SetActive(true);
+    return;
+  }
+
+  // If the change in phase is greater than the change threshold in either
+  // direction, request an immediate reset. This logic might result in a false
+  // negative if there is a simultaneous small change in the interval and the
+  // fmod just happens to return something near zero. Assuming the timebase
+  // is very recent though, which it should be, we'll still be ok because the
+  // old clock and new clock just happen to line up.
+  double target_delta =
+      std::abs((timebase - current_parameters_.tick_target).InSecondsF());
+  double phase_change =
+      fmod(target_delta, interval.InSecondsF()) / interval.InSecondsF();
+  if (phase_change > kPhaseChangeThreshold &&
+      phase_change < (1.0 - kPhaseChangeThreshold)) {
+    TRACE_EVENT_INSTANT0("cc", "DelayBasedTimeSource::PhaseChanged",
+                         TRACE_EVENT_SCOPE_THREAD);
+    SetActive(false);
+    SetActive(true);
+    return;
+  }
+}
+
+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)
+base::TimeTicks DelayBasedTimeSource::NextTickTarget(base::TimeTicks now) {
+  base::TimeTicks new_tick_target = now.SnappedToNextTick(
+      next_parameters_.tick_target, next_parameters_.interval);
+  DCHECK(now <= new_tick_target)
+      << "now = " << now.ToInternalValue()
+      << "; new_tick_target = " << new_tick_target.ToInternalValue()
+      << "; new_interval = " << next_parameters_.interval.InMicroseconds()
+      << "; tick_target = " << next_parameters_.tick_target.ToInternalValue();
+
+  // Avoid double ticks when:
+  // 1) Turning off the timer and turning it right back on.
+  // 2) Jittery data is passed to SetTimebaseAndInterval().
+  if (new_tick_target - last_tick_time_ <=
+      next_parameters_.interval / kDoubleTickDivisor)
+    new_tick_target += next_parameters_.interval;
+
+  return new_tick_target;
+}
+
+void DelayBasedTimeSource::PostNextTickTask(base::TimeTicks now) {
+  base::TimeTicks new_tick_target = NextTickTarget(now);
+
+  // Post another task *before* the tick and update state
+  base::TimeDelta delay;
+  if (now <= new_tick_target)
+    delay = new_tick_target - now;
+  task_runner_->PostDelayedTask(FROM_HERE,
+                                base::Bind(&DelayBasedTimeSource::OnTimerFired,
+                                           weak_factory_.GetWeakPtr()),
+                                delay);
+
+  next_parameters_.tick_target = new_tick_target;
+  current_parameters_ = next_parameters_;
+}
+
+std::string DelayBasedTimeSource::TypeString() const {
+  return "DelayBasedTimeSource";
+}
+
+std::string DelayBasedTimeSourceHighRes::TypeString() const {
+  return "DelayBasedTimeSourceHighRes";
+}
+
+void DelayBasedTimeSource::AsValueInto(
+    base::trace_event::TracedValue* state) const {
+  state->SetString("type", TypeString());
+  state->SetDouble("last_tick_time_us", LastTickTime().ToInternalValue());
+  state->SetDouble("next_tick_time_us", NextTickTime().ToInternalValue());
+
+  state->BeginDictionary("current_parameters");
+  state->SetDouble("interval_us",
+                   current_parameters_.interval.InMicroseconds());
+  state->SetDouble("tick_target_us",
+                   current_parameters_.tick_target.ToInternalValue());
+  state->EndDictionary();
+
+  state->BeginDictionary("next_parameters");
+  state->SetDouble("interval_us", next_parameters_.interval.InMicroseconds());
+  state->SetDouble("tick_target_us",
+                   next_parameters_.tick_target.ToInternalValue());
+  state->EndDictionary();
+
+  state->SetBoolean("active", active_);
+}
+
+}  // namespace cc