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* Copyright (C) 2012 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#pragma once
#include <stddef.h>
#include <utils/Mutex.h>
#include <utils/RefBase.h>
#include <utils/Timers.h>
#include <ui/FenceTime.h>
#include <memory>
namespace android {
class FenceTime;
class DispSync {
class Callback {
Callback() = default;
virtual ~Callback();
virtual void onDispSyncEvent(nsecs_t when, nsecs_t expectedVSyncTimestamp) = 0;
Callback(Callback const&) = delete;
Callback& operator=(Callback const&) = delete;
DispSync() = default;
virtual ~DispSync();
virtual void reset() = 0;
virtual bool addPresentFence(const std::shared_ptr<FenceTime>&) = 0;
virtual void beginResync() = 0;
virtual bool addResyncSample(nsecs_t timestamp, std::optional<nsecs_t> hwcVsyncPeriod,
bool* periodFlushed) = 0;
virtual void endResync() = 0;
virtual void setPeriod(nsecs_t period) = 0;
virtual nsecs_t getPeriod() = 0;
virtual status_t addEventListener(const char* name, nsecs_t phase, Callback* callback,
nsecs_t lastCallbackTime) = 0;
virtual status_t removeEventListener(Callback* callback, nsecs_t* outLastCallback) = 0;
virtual status_t changePhaseOffset(Callback* callback, nsecs_t phase) = 0;
virtual nsecs_t computeNextRefresh(int periodOffset, nsecs_t now) const = 0;
virtual void setIgnorePresentFences(bool ignore) = 0;
virtual nsecs_t expectedPresentTime(nsecs_t now) = 0;
virtual void dump(std::string& result) const = 0;
DispSync(DispSync const&) = delete;
DispSync& operator=(DispSync const&) = delete;
namespace impl {
class DispSyncThread;
// DispSync maintains a model of the periodic hardware-based vsync events of a
// display and uses that model to execute period callbacks at specific phase
// offsets from the hardware vsync events. The model is constructed by
// feeding consecutive hardware event timestamps to the DispSync object via
// the addResyncSample method.
// The model is validated using timestamps from Fence objects that are passed
// to the DispSync object via the addPresentFence method. These fence
// timestamps should correspond to a hardware vsync event, but they need not
// be consecutive hardware vsync times. If this method determines that the
// current model accurately represents the hardware event times it will return
// false to indicate that a resynchronization (via addResyncSample) is not
// needed.
class DispSync : public android::DispSync {
// hasSyncFramework specifies whether the platform supports present fences.
DispSync(const char* name, bool hasSyncFramework);
~DispSync() override;
// reset clears the resync samples and error value.
void reset() override;
// addPresentFence adds a fence for use in validating the current vsync
// event model. The fence need not be signaled at the time
// addPresentFence is called. When the fence does signal, its timestamp
// should correspond to a hardware vsync event. Unlike the
// addResyncSample method, the timestamps of consecutive fences need not
// correspond to consecutive hardware vsync events.
// This method should be called with the retire fence from each HWComposer
// set call that affects the display.
bool addPresentFence(const std::shared_ptr<FenceTime>& fenceTime) override;
// The beginResync, addResyncSample, and endResync methods are used to re-
// synchronize the DispSync's model to the hardware vsync events. The re-
// synchronization process involves first calling beginResync, then
// calling addResyncSample with a sequence of consecutive hardware vsync
// event timestamps, and finally calling endResync when addResyncSample
// indicates that no more samples are needed by returning false.
// This resynchronization process should be performed whenever the display
// is turned on (i.e. once immediately after it's turned on) and whenever
// addPresentFence returns true indicating that the model has drifted away
// from the hardware vsync events.
void beginResync() override;
// Adds a vsync sample to the dispsync model. The timestamp is the time
// of the vsync event that fired. periodFlushed will return true if the
// vsync period was detected to have changed to mPendingPeriod.
// This method will return true if more vsync samples are needed to lock
// down the DispSync model, and false otherwise.
// periodFlushed will be set to true if mPendingPeriod is flushed to
// mIntendedPeriod, and false otherwise.
bool addResyncSample(nsecs_t timestamp, std::optional<nsecs_t> hwcVsyncPeriod,
bool* periodFlushed) override;
void endResync() override;
// The setPeriod method sets the vsync event model's period to a specific
// value. This should be used to prime the model when a display is first
// turned on, or when a refresh rate change is requested.
void setPeriod(nsecs_t period) override;
// The getPeriod method returns the current vsync period.
nsecs_t getPeriod() override;
// addEventListener registers a callback to be called repeatedly at the
// given phase offset from the hardware vsync events. The callback is
// called from a separate thread and it should return reasonably quickly
// (i.e. within a few hundred microseconds).
// If the callback was previously registered, and the last clock time the
// callback was invoked was known to the caller (e.g. via removeEventListener),
// then the caller may pass that through to lastCallbackTime, so that
// callbacks do not accidentally double-fire if they are unregistered and
// reregistered in rapid succession.
status_t addEventListener(const char* name, nsecs_t phase, Callback* callback,
nsecs_t lastCallbackTime) override;
// removeEventListener removes an already-registered event callback. Once
// this method returns that callback will no longer be called by the
// DispSync object.
// outLastCallbackTime will contain the last time that the callback was invoked.
// If the caller wishes to reregister the same callback, they should pass the
// callback time back into lastCallbackTime (see addEventListener).
status_t removeEventListener(Callback* callback, nsecs_t* outLastCallbackTime) override;
// changePhaseOffset changes the phase offset of an already-registered event callback. The
// method will make sure that there is no skipping or double-firing on the listener per frame,
// even when changing the offsets multiple times.
status_t changePhaseOffset(Callback* callback, nsecs_t phase) override;
// computeNextRefresh computes when the next refresh is expected to begin.
// The periodOffset value can be used to move forward or backward; an
// offset of zero is the next refresh, -1 is the previous refresh, 1 is
// the refresh after next. etc.
nsecs_t computeNextRefresh(int periodOffset, nsecs_t now) const override;
// In certain situations the present fences aren't a good indicator of vsync
// time, e.g. when vr flinger is active, or simply aren't available,
// e.g. when the sync framework isn't present. Use this method to toggle
// whether or not DispSync ignores present fences. If present fences are
// ignored, DispSync will always ask for hardware vsync events by returning
// true from addPresentFence() and addResyncSample().
void setIgnorePresentFences(bool ignore) override;
// Determine the expected present time when a buffer acquired now will be displayed.
nsecs_t expectedPresentTime(nsecs_t now);
// dump appends human-readable debug info to the result string.
void dump(std::string& result) const override;
void updateModelLocked();
void updateErrorLocked();
void resetLocked();
void resetErrorLocked();
enum { MAX_RESYNC_SAMPLES = 32 };
const char* const mName;
// mPeriod is the computed period of the modeled vsync events in
// nanoseconds.
nsecs_t mPeriod;
// mIntendedPeriod is the intended period of the modeled vsync events in
// nanoseconds. Under ideal conditions this should be similar if not the
// same as mPeriod, plus or minus an observed error.
nsecs_t mIntendedPeriod = 0;
// mPendingPeriod is the proposed period change in nanoseconds.
// If mPendingPeriod differs from mPeriod and is nonzero, it will
// be flushed to mPeriod when we detect that the hardware switched
// vsync frequency.
nsecs_t mPendingPeriod = 0;
// mPhase is the phase offset of the modeled vsync events. It is the
// number of nanoseconds from time 0 to the first vsync event.
nsecs_t mPhase;
// mReferenceTime is the reference time of the modeled vsync events.
// It is the nanosecond timestamp of the first vsync event after a resync.
nsecs_t mReferenceTime;
// mError is the computed model error. It is based on the difference
// between the estimated vsync event times and those observed in the
// mPresentFences array.
nsecs_t mError;
// mZeroErrSamplesCount keeps track of how many times in a row there were
// zero timestamps available in the mPresentFences array.
// Used to sanity check that we are able to calculate the model error.
size_t mZeroErrSamplesCount;
// Whether we have updated the vsync event model since the last resync.
bool mModelUpdated;
// These member variables are the state used during the resynchronization
// process to store information about the hardware vsync event times used
// to compute the model.
nsecs_t mResyncSamples[MAX_RESYNC_SAMPLES] = {0};
size_t mFirstResyncSample = 0;
size_t mNumResyncSamples = 0;
int mNumResyncSamplesSincePresent;
// These member variables store information about the present fences used
// to validate the currently computed model.
std::shared_ptr<FenceTime> mPresentFences[NUM_PRESENT_SAMPLES]{FenceTime::NO_FENCE};
size_t mPresentSampleOffset;
// mThread is the thread from which all the callbacks are called.
sp<DispSyncThread> mThread;
// mMutex is used to protect access to all member variables.
mutable Mutex mMutex;
// Ignore present (retire) fences if the device doesn't have support for the
// sync framework
bool mIgnorePresentFences;
std::unique_ptr<Callback> mZeroPhaseTracer;
// Flag to turn on logging in systrace.
bool mTraceDetailedInfo = false;
} // namespace impl
} // namespace android