Initial checkin of the new Mozart compositor.

services/gfx/compositor/backend/vsync_scheduler.cc

Index: services/gfx/compositor/backend/vsync_scheduler.cc
diff --git a/services/gfx/compositor/backend/vsync_scheduler.cc b/services/gfx/compositor/backend/vsync_scheduler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..71be4f33a5f840fb8a8404a1643eae74b473a3d2
--- /dev/null
+++ b/services/gfx/compositor/backend/vsync_scheduler.cc
@@ -0,0 +1,273 @@
+// Copyright 2015 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 "services/gfx/compositor/backend/vsync_scheduler.h"
+
+#include <algorithm>
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/time/time.h"
+
+namespace compositor {
+
+constexpr int64_t VsyncScheduler::kMinVsyncInterval;
+constexpr int64_t VsyncScheduler::kMaxVsyncInterval;
+
+VsyncScheduler::VsyncScheduler(
+    const scoped_refptr<base::TaskRunner>& task_runner,
+    const SchedulerCallbacks& callbacks)
+    : VsyncScheduler(task_runner, callbacks, base::Bind(&MojoGetTimeTicksNow)) {
+}
+
+VsyncScheduler::VsyncScheduler(
+    const scoped_refptr<base::TaskRunner>& task_runner,
+    const SchedulerCallbacks& callbacks,
+    const Clock& clock)
+    : state_(std::make_shared<State>(task_runner, callbacks, clock)) {}
+
+VsyncScheduler::~VsyncScheduler() {}
+
+void VsyncScheduler::ScheduleFrame(SchedulingMode scheduling_mode) {
+  state_->ScheduleFrame(scheduling_mode);
+}
+
+VsyncScheduler::State::State(const scoped_refptr<base::TaskRunner>& task_runner,
+                             const SchedulerCallbacks& callbacks,
+                             const Clock& clock)
+    : task_runner_(task_runner), callbacks_(callbacks), clock_(clock) {}
+
+VsyncScheduler::State::~State() {}
+
+bool VsyncScheduler::State::Start(int64_t vsync_timebase,
+                                  int64_t vsync_interval,
+                                  int64_t update_phase,
+                                  int64_t snapshot_phase,
+                                  int64_t presentation_phase) {
+  // Be slightly paranoid.  Timing glitches are hard to find and the
+  // vsync parameters will typically come from other services.
+  // Ensure vsync timing is anchored on actual observations from the past.
+  MojoTimeTicks now = GetTimeTicksNow();
+  if (vsync_timebase > now) {
+    DVLOG(1) << "Vsync timebase is in the future: vsync_timebase="
+             << vsync_timebase << ", now=" << now;
+    return false;
+  }
+  if (vsync_interval < kMinVsyncInterval ||
+      vsync_interval > kMaxVsyncInterval) {
+    DVLOG(1) << "Vsync interval is invalid: vsync_interval=" << vsync_interval
+             << ", min=" << kMinVsyncInterval << ", max=" << kMaxVsyncInterval;
+    return false;
+  }
+  if (snapshot_phase < update_phase ||
+      snapshot_phase > update_phase + vsync_interval ||
+      presentation_phase < snapshot_phase) {
+    // Updating and snapshotting must happen within the same frame interval
+    // to avoid having multiple updates in progress simultanteously (which
+    // doesn't make much sense if we're already compute bound).
+    DVLOG(1) << "Vsync scheduling phases are invalid: update_phase="
+             << update_phase << ", snapshot_phase=" << snapshot_phase
+             << ", presentation_phase=" << presentation_phase;
+    return false;
+  }
+
+  {
+    std::lock_guard<std::mutex> lock(mutex_);
+
+    // Suppress spurious updates.
+    if (running_ && vsync_timebase_ == vsync_timebase &&
+        vsync_interval_ == vsync_interval && update_phase_ == update_phase &&
+        snapshot_phase_ == snapshot_phase &&
+        presentation_phase_ == presentation_phase)
+      return true;
+
+    // Get running with these new parameters.
+    // Note that |last_delivered_update_time_| is preserved.
+    running_ = true;
+    generation_++;  // cancels pending undelivered callbacks
+    vsync_timebase_ = vsync_timebase;
+    vsync_interval_ = vsync_interval;
+    update_phase_ = update_phase;
+    snapshot_phase_ = snapshot_phase;
+    presentation_phase_ = presentation_phase;
+    need_update_ = true;
+    pending_dispatch_ = false;
+    ScheduleLocked(now);
+    return true;
+  }
+}
+
+void VsyncScheduler::State::Stop() {
+  std::lock_guard<std::mutex> lock(mutex_);
+  running_ = false;
+}
+
+void VsyncScheduler::State::ScheduleFrame(SchedulingMode scheduling_mode) {
+  MojoTimeTicks now = GetTimeTicksNow();
+
+  {
+    std::lock_guard<std::mutex> lock(mutex_);
+    if (running_) {
+      if (scheduling_mode == SchedulingMode::kUpdateAndSnapshot)
+        need_update_ = true;
+      ScheduleLocked(now);
+    }
+  }
+}
+
+void VsyncScheduler::State::ScheduleLocked(MojoTimeTicks now) {
+  DCHECK(running_);
+  DCHECK(now >= vsync_timebase_);
+  DVLOG(2) << "schedule: now=" << now << ", need_update_=" << need_update_
+           << ", last_delivered_update_time_=" << last_delivered_update_time_;
+  if (pending_dispatch_)
+    return;
+
+  // Determine the time of the earliest achievable frame snapshot in
+  // the near future.
+  int64_t snapshot_timebase = vsync_timebase_ + snapshot_phase_;
+  uint64_t snapshot_offset = (now - snapshot_timebase) % vsync_interval_;
+  int64_t snapshot_time = now - snapshot_offset + vsync_interval_;
+  DCHECK(snapshot_time >= now);
+
+  // Determine when the update that produced this snapshot must have begun.
+  // This time may be in the past.
+  int64_t update_time = snapshot_time - snapshot_phase_ + update_phase_;
+  DCHECK(update_time <= snapshot_time);
+
+  // When changing vsync parameters, it's possible for the next update time
+  // to regress.  Prevent applications from observing that.
+  if (update_time <= last_delivered_update_time_) {
+    int64_t frames =
+        (last_delivered_update_time_ - update_time) / vsync_interval_ + 1;
+    int64_t adjustment = frames * vsync_interval_;
+    update_time += adjustment;
+    snapshot_time += adjustment;
+  }
+
+  // Schedule dispatching at that time.
+  if (update_time >= now) {
+    PostDispatchLocked(now, update_time, Action::kUpdate, update_time);
+  } else {
+    PostDispatchLocked(now, snapshot_time, Action::kEarlySnapshot, update_time);
+  }
+
+  pending_dispatch_ = true;
+}
+
+void VsyncScheduler::State::PostDispatchLocked(int64_t now,
+                                               int64_t delivery_time,
+                                               Action action,
+                                               int64_t update_time) {
+  DVLOG(2) << "post: now=" << now << ", delivery_time=" << delivery_time
+           << ", action=" << static_cast<int>(action)
+           << ", update_time=" << update_time;
+
+  task_runner_->PostDelayedTask(
+      FROM_HERE,
+      base::Bind(&VsyncScheduler::State::DispatchThunk, shared_from_this(),
+                 generation_, action, update_time),
+      base::TimeDelta::FromMicroseconds(
+          std::max(delivery_time - now, static_cast<int64_t>(0))));
+}
+
+void VsyncScheduler::State::DispatchThunk(
+    const std::weak_ptr<State>& state_weak,
+    int32_t generation,
+    Action action,
+    int64_t update_time) {
+  std::shared_ptr<State> state = state_weak.lock();
+  if (state)
+    state->Dispatch(generation, action, update_time);
+}
+
+void VsyncScheduler::State::Dispatch(int32_t generation,
+                                     Action action,
+                                     int64_t update_time) {
+  MojoTimeTicks now = GetTimeTicksNow();
+  DCHECK(update_time <= now);
+
+  // Time may have passed since the callback was originally scheduled and
+  // it's possible that we completely missed the deadline we were aiming for.
+  // Reevaluate the schedule and jump ahead if necessary.
+  mojo::gfx::composition::FrameInfo frame_info;
+  {
+    std::lock_guard<std::mutex> lock(mutex_);
+    if (!running_ || generation_ != generation)
+      return;
+
+    DCHECK(pending_dispatch_);
+
+    // Check whether we missed any deadlines.
+    bool missed_deadline = false;
+    if (action == Action::kUpdate) {
+      int64_t update_deadline = update_time - update_phase_ + snapshot_phase_;
+      if (now > update_deadline) {
+        LOG(WARNING) << "Compositor missed update deadline by "
+                     << (now - update_deadline) << " us";
+        missed_deadline = true;
+      }
+    } else {
+      int64_t snapshot_deadline = update_time + vsync_interval_;
+      if (now > snapshot_deadline) {
+        LOG(WARNING) << "Compositor missed snapshot deadline by "
+                     << (now - snapshot_deadline) << " us";
+        missed_deadline = true;
+      }
+    }
+    if (missed_deadline) {
+      uint64_t offset = (now - update_time) % vsync_interval_;
+      update_time = now - offset;
+      DCHECK(update_time > now - vsync_interval_ && update_time <= now);
+    }
+
+    DVLOG(2) << "dispatch: now=" << now
+             << ", action=" << static_cast<int>(action)
+             << ", update_time=" << update_time;
+
+    // Schedule the corresponding snapshot for the update.
+    if (action == Action::kUpdate) {
+      int64_t snapshot_time = update_time - update_phase_ + snapshot_phase_;
+      PostDispatchLocked(now, snapshot_time, Action::kLateSnapshot,
+                         update_time);
+      need_update_ = false;
+    } else if (need_update_) {
+      int64_t next_update_time = update_time + vsync_interval_;
+      PostDispatchLocked(now, next_update_time, Action::kUpdate,
+                         next_update_time);
+
+      // If we missed the deadline on an early snapshot, then just skip it
+      // and wait for the following update instead.
+      if (action == Action::kEarlySnapshot && missed_deadline) {
+        DVLOG(2) << "skip early snapshot";
+        return;
+      }
+    } else {
+      pending_dispatch_ = false;
+    }
+
+    SetFrameInfoLocked(&frame_info, update_time);
+    last_delivered_update_time_ = update_time;
+  }
+
+  if (action == Action::kUpdate) {
+    callbacks_.update_callback.Run(frame_info);
+  } else {
+    callbacks_.snapshot_callback.Run(frame_info);
+  }
+}
+
+void VsyncScheduler::State::SetFrameInfoLocked(
+    mojo::gfx::composition::FrameInfo* frame_info,
+    int64_t update_time) {
+  DCHECK(frame_info);
+  frame_info->frame_time = update_time;
+  frame_info->frame_interval = vsync_interval_;
+  frame_info->frame_deadline = update_time - update_phase_ + snapshot_phase_;
+  frame_info->presentation_time =
+      update_time - update_phase_ + presentation_phase_;
+}
+
+}  // namespace compositor