Initial checkin of the new Mozart compositor.

services/gfx/compositor/backend/vsync_scheduler.h

+// 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.
+
+#ifndef SERVICES_GFX_COMPOSITOR_BACKEND_VSYNC_SCHEDULER_H_
+#define SERVICES_GFX_COMPOSITOR_BACKEND_VSYNC_SCHEDULER_H_
+
+#include <limits>
+#include <memory>
+#include <mutex>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/task_runner.h"
+#include "services/gfx/compositor/backend/scheduler.h"
+
+namespace compositor {
+
+// Schedules work to coincide with vsync intervals.
+//
+// This object is thread-safe and it intended to be used to allow one thread
+// to be scheduling work for itself while another thread concurrently updates
+// timing parameters.
+class VsyncScheduler : public Scheduler {
+ public:
+  // Limits on allowable parameters.  (Exposed for testing.)
+  static constexpr int64_t kMinVsyncInterval = 1000;     // 1000 Hz

[viettrungluu, 2016/01/04 21:08:24]

You need to declare storage for these (in the .cc) file. (Otherwise, you'd
probably get a link error if someone ever needed to use
&VsyncScheduler::kMinVsyncInterval, or sometimes when calling a function that
takes a reference argument[*] at low optimization levels.)

[*] It's pretty stupid to take a |const int64_t&| argument, but you run into
this with templated stuff (e.g., STL containers).

[jeffbrown, 2016/01/16 03:28:31]

Hah!  You're right.  I'd interpreted constexpr as meaning a "compile time only
constant expression" but it turns out it needs storage just like "const".  Oh
well.

+  static constexpr int64_t kMaxVsyncInterval = 1000000;  // 1 Hz
+
+  // Time reference.  Should be MojoTimeTicksNow() except during testing.
+  using Clock = base::Callback<MojoTimeTicks()>;
+
+  VsyncScheduler(const scoped_refptr<base::TaskRunner>& task_runner,
+                 const SchedulerCallbacks& callbacks);
+  VsyncScheduler(const scoped_refptr<base::TaskRunner>& task_runner,
+                 const SchedulerCallbacks& callbacks,
+                 const Clock& clock);
+  ~VsyncScheduler() override;
+
+  // Starts scheduling work and sets the scheduling parameters.
+  //
+  // |vsync_timebase| is a value in the |MojoTimeTicks| timebase which
+  // specifies when a recent vsync occurred and is used to determine the phase.
+  //
+  // |vsync_interval| is the number of microseconds between vsyncs which
+  // also determines the |FrameInfo.frame_interval| value to deliver to
+  // applications.
+  //
+  // |update_phase| specifies an offset relative to vsync for determining
+  // when updates are scheduled and the |FrameInfo.frame_time| to deliver
+  // to applications.
+  //
+  // |snapshot_phase| specifies an offset relative to vsync for
+  // determining when snapshots are scheduled and the |FrameInfo.frame_deadline|
+  // to deliver to applications.  Must be greater than or equal to
+  // |update_phase|.
+  //
+  // |presentation_phase| specifies an offset relative to vsync for
+  // determining when frames are shown on the display output and the
+  // |FrameInfo.presentation_time| to deliver to applications.  Must be
+  // greater than or equal to |snapshot_phase|.
+  //
+  // The notion of 'vsync' is somewhat abstract here.  It's just a reference
+  // pulse but we usually interpret it as a deadline for preparing the next
+  // frame and submitting it to the display hardware.
+  //
+  // The phases can be positive or negative but negative offsets from vsync
+  // may be easier to interpret when computing deadlines.  To avoid
+  // overflows, the values chosen for the phases should be close to 0.
+  //
+  // This function schedules an update and snapshot if not already scheduled.
+  //
+  // Returns true if the schedule was started successfully, false if the
+  // parameters are invalid.
+  bool Start(int64_t vsync_timebase,
+             int64_t vsync_interval,
+             int64_t update_phase,
+             int64_t snapshot_phase,
+             int64_t presentation_phase) {
+    return state_->Start(vsync_timebase, vsync_interval, update_phase,
+                         snapshot_phase, presentation_phase);
+  }
+
+  // Stops scheduling work.
+  //
+  // Previously scheduled callbacks may still be delivered.
+  void Stop() { state_->Stop(); }
+
+  // |Scheduler|:
+  void ScheduleFrame(SchedulingMode scheduling_mode) override;
+
+ private:
+  // Internal state.  Held by a shared_ptr so that callbacks running on
+  // other threads can reference it using a weak_ptr.
+  class State : public std::enable_shared_from_this<State> {
+   public:
+    State(const scoped_refptr<base::TaskRunner>& task_runner,
+          const SchedulerCallbacks& callbacks,
+          const Clock& clock);
+    ~State();
+
+    MojoTimeTicks GetTimeTicksNow() { return clock_.Run(); }
+
+    bool Start(int64_t vsync_timebase,
+               int64_t vsync_interval,
+               int64_t update_phase,
+               int64_t snapshot_phase,
+               int64_t presentation_phase);
+    void Stop();
+    void ScheduleFrame(SchedulingMode scheduling_mode);
+
+   private:
+    enum class Action {
+      kUpdate,
+      kEarlySnapshot,
+      kLateSnapshot,
+    };
+
+    static void DispatchThunk(const std::weak_ptr<State>& state_weak,
+                              int32_t generation,
+                              Action action,
+                              int64_t update_time);
+
+    void ScheduleLocked(MojoTimeTicks now);
+    void PostDispatchLocked(int64_t now,
+                            int64_t delivery_time,
+                            Action action,
+                            int64_t update_time);
+
+    void Dispatch(int32_t generation, Action action, int64_t update_time);
+    void SetFrameInfoLocked(mojo::gfx::composition::FrameInfo* frame_info,
+                            int64_t update_time);
+
+    const scoped_refptr<base::TaskRunner> task_runner_;
+    const SchedulerCallbacks callbacks_;
+    const Clock clock_;
+
+    // Parameters and state guarded by |mutex_|.
+    std::mutex mutex_;
+    bool running_ = false;
+    int32_t generation_ = 0;
+    int64_t vsync_timebase_ = 0;
+    int64_t vsync_interval_ = 0;
+    int64_t update_phase_ = 0;
+    int64_t snapshot_phase_ = 0;
+    int64_t presentation_phase_ = 0;
+    bool need_update_ = false;
+    bool pending_dispatch_ = false;
+    int64_t last_delivered_update_time_ = std::numeric_limits<int64_t>::min();
+
+    DISALLOW_COPY_AND_ASSIGN(State);
+  };
+
+  const std::shared_ptr<State> state_;
+
+  DISALLOW_COPY_AND_ASSIGN(VsyncScheduler);
+};
+
+}  // namespace compositor
+
+#endif  // SERVICES_GFX_COMPOSITOR_BACKEND_VSYNC_SCHEDULER_H_