SF: add VSyncDispatch

Add a low level timer primitive to arrange for calling a
callback relative to an anticipated vsync time.

This defines vsync offsets in terms of time remaining until the
targeted vsync event, which is a rate independent definition.

Bug: 140301853
Test: 31 new unit tests
Change-Id: I6ac8f05e4c2107755493b2709551773d0e79c17d
diff --git a/services/surfaceflinger/Scheduler/VSyncDispatch.h b/services/surfaceflinger/Scheduler/VSyncDispatch.h
new file mode 100644
index 0000000..0050495
--- /dev/null
+++ b/services/surfaceflinger/Scheduler/VSyncDispatch.h
@@ -0,0 +1,230 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <android-base/thread_annotations.h>
+#include <utils/Timers.h>
+#include <functional>
+#include <memory>
+#include <mutex>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+
+#include "StrongTyping.h"
+
+namespace android::scheduler {
+class TimeKeeper;
+class VSyncTracker;
+
+enum class ScheduleResult { Scheduled, ReScheduled, CannotSchedule, Error };
+enum class CancelResult { Cancelled, TooLate, Error };
+
+namespace impl {
+
+// VSyncDispatchEntry is a helper class representing internal state for each entry in VSyncDispatch
+// hoisted to public for unit testing.
+class VSyncDispatchEntry {
+public:
+    // This is the state of the entry. There are 3 states, armed, running, disarmed.
+    // Valid transition: disarmed -> armed ( when scheduled )
+    // Valid transition: armed -> running -> disarmed ( when timer is called)
+    // Valid transition: armed -> disarmed ( when cancelled )
+    VSyncDispatchEntry(std::string const& name, std::function<void(nsecs_t)> const& fn);
+    std::string_view name() const;
+
+    // Start: functions that are not threadsafe.
+    // Return the last vsync time this callback was invoked.
+    std::optional<nsecs_t> lastExecutedVsyncTarget() const;
+
+    // This moves the state from disarmed->armed and will calculate the wakeupTime.
+    nsecs_t schedule(nsecs_t workDuration, nsecs_t earliestVsync, VSyncTracker& tracker,
+                     nsecs_t now);
+    // This will update armed entries with the latest vsync information. Entry remains armed.
+    void update(VSyncTracker& tracker, nsecs_t now);
+
+    // This will return empty if not armed, or the next calculated wakeup time if armed.
+    // It will not update the wakeupTime.
+    std::optional<nsecs_t> wakeupTime() const;
+
+    // This moves state from armed->disarmed.
+    void disarm();
+
+    // This moves the state from armed->running.
+    // Store the timestamp that this was intended for as the last called timestamp.
+    nsecs_t executing();
+    // End: functions that are not threadsafe.
+
+    // Invoke the callback with the timestamp, moving the state from running->disarmed.
+    void callback(nsecs_t timestamp);
+    // Block calling thread while the callback is executing.
+    void ensureNotRunning();
+
+private:
+    void arm(VSyncTracker& tracker, nsecs_t now);
+    std::string const mName;
+    std::function<void(nsecs_t)> const mCallback;
+
+    nsecs_t mWorkDuration;
+    nsecs_t mEarliestVsync;
+
+    struct ArmingInfo {
+        nsecs_t mActualWakeupTime;
+        nsecs_t mActualVsyncTime;
+    };
+    std::optional<ArmingInfo> mArmedInfo;
+    std::optional<nsecs_t> mLastDispatchTime;
+
+    std::mutex mRunningMutex;
+    std::condition_variable mCv;
+    bool mRunning GUARDED_BY(mRunningMutex) = false;
+};
+
+} // namespace impl
+
+/*
+ * VSyncDispatch is a class that will dispatch callbacks relative to system vsync events.
+ */
+class VSyncDispatch {
+public:
+    using CallbackToken = StrongTyping<size_t, class CallbackTokenTag, Compare>;
+
+    /* creates a VsyncDispatch.
+     * \param [in]  a timekeeper object for dispatching events.
+     * \param [in]  a tracker object that is monitoring expected vsync events.
+     * \param [in]  a tunable in nanoseconds that indicates when events that fall close together
+     *              should be dispatched in one timer wakeup.
+     */
+    explicit VSyncDispatch(std::unique_ptr<TimeKeeper> tk, VSyncTracker& tracker,
+                           nsecs_t timerSlack);
+    ~VSyncDispatch();
+
+    /*
+     * Registers a callback that will be called at designated points on the vsync timeline.
+     * The callback can be scheduled, rescheduled targeting vsync times, or cancelled.
+     * The token returned must be cleaned up via unregisterCallback.
+     *
+     * \param [in] callbackFn   A function to schedule for callback. The resources needed to invoke
+     *                          callbackFn must have lifetimes encompassing the lifetime of the
+     *                          CallbackToken returned.
+     * \param [in] callbackName A human-readable, unique name to identify the callback.
+     * \return                  A token that can be used to schedule, reschedule, or cancel the
+     *                          invocation of callbackFn.
+     *
+     */
+    CallbackToken registerCallback(std::function<void(nsecs_t)> const& callbackFn,
+                                   std::string callbackName);
+
+    /*
+     * Unregisters a callback.
+     *
+     * \param [in] token        The callback to unregister.
+     *
+     */
+    void unregisterCallback(CallbackToken token);
+
+    /*
+     * Schedules the registered callback to be dispatched.
+     *
+     * The callback will be dispatched at 'workDuration' nanoseconds before a vsync event.
+     *
+     * The caller designates the earliest vsync event that should be targeted by the earliestVsync
+     * parameter.
+     * The callback will be scheduled at (workDuration - predictedVsync), where predictedVsync
+     * is the first vsync event time where ( predictedVsync >= earliestVsync ).
+     *
+     * If (workDuration - earliestVsync) is in the past, or if a callback has already been
+     * dispatched for the predictedVsync, an error will be returned.
+     *
+     * It is valid to reschedule a callback to a different time.
+     *
+     * \param [in] token           The callback to schedule.
+     * \param [in] workDuration    The time before the actual vsync time to invoke the callback
+     *                             associated with token.
+     * \param [in] earliestVsync   The targeted display time. This will be snapped to the closest
+     *                             predicted vsync time after earliestVsync.
+     * \return                     A ScheduleResult::Scheduled if callback was scheduled.
+     *                             A ScheduleResult::ReScheduled if callback was rescheduled.
+     *                             A ScheduleResult::CannotSchedule
+     *                             if (workDuration - earliestVsync) is in the past, or
+     *                             if a callback was dispatched for the predictedVsync already.
+     *                             A ScheduleResult::Error if there was another error.
+     */
+    ScheduleResult schedule(CallbackToken token, nsecs_t workDuration, nsecs_t earliestVsync);
+
+    /* Cancels a scheduled callback, if possible.
+     *
+     * \param [in] token    The callback to cancel.
+     * \return              A CancelResult::TooLate if the callback was already dispatched.
+     *                      A CancelResult::Cancelled if the callback was successfully cancelled.
+     *                      A CancelResult::Error if there was an pre-condition violation.
+     */
+    CancelResult cancel(CallbackToken token);
+
+private:
+    VSyncDispatch(VSyncDispatch const&) = delete;
+    VSyncDispatch& operator=(VSyncDispatch const&) = delete;
+
+    using CallbackMap = std::unordered_map<size_t, std::shared_ptr<impl::VSyncDispatchEntry>>;
+
+    void timerCallback();
+    void setTimer(nsecs_t, nsecs_t) REQUIRES(mMutex);
+    void rearmTimer(nsecs_t now) REQUIRES(mMutex);
+    void rearmTimerSkippingUpdateFor(nsecs_t now, CallbackMap::iterator const& skipUpdate)
+            REQUIRES(mMutex);
+    void cancelTimer() REQUIRES(mMutex);
+
+    static constexpr nsecs_t kInvalidTime = std::numeric_limits<int64_t>::max();
+    std::unique_ptr<TimeKeeper> const mTimeKeeper;
+    VSyncTracker& mTracker;
+    nsecs_t const mTimerSlack;
+
+    std::mutex mutable mMutex;
+    size_t mCallbackToken GUARDED_BY(mMutex) = 0;
+
+    CallbackMap mCallbacks GUARDED_BY(mMutex);
+    nsecs_t mIntendedWakeupTime GUARDED_BY(mMutex) = kInvalidTime;
+};
+
+/*
+ * Helper class to operate on registered callbacks. It is up to user of the class to ensure
+ * that VsyncDispatch lifetime exceeds the lifetime of VSyncCallbackRegistation.
+ */
+class VSyncCallbackRegistration {
+public:
+    VSyncCallbackRegistration(VSyncDispatch&, std::function<void(nsecs_t)> const& callbackFn,
+                              std::string const& callbackName);
+    VSyncCallbackRegistration(VSyncCallbackRegistration&&);
+    VSyncCallbackRegistration& operator=(VSyncCallbackRegistration&&);
+    ~VSyncCallbackRegistration();
+
+    // See documentation for VSyncDispatch::schedule.
+    ScheduleResult schedule(nsecs_t workDuration, nsecs_t earliestVsync);
+
+    // See documentation for VSyncDispatch::cancel.
+    CancelResult cancel();
+
+private:
+    VSyncCallbackRegistration(VSyncCallbackRegistration const&) = delete;
+    VSyncCallbackRegistration& operator=(VSyncCallbackRegistration const&) = delete;
+
+    std::reference_wrapper<VSyncDispatch> mDispatch;
+    VSyncDispatch::CallbackToken mToken;
+    bool mValidToken;
+};
+
+} // namespace android::scheduler