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// Copyright 2014 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 <set>
#include <string>
#include "base/location.h"
#include "base/trace_event/trace_event.h"
#include "base/trace_event/trace_event_argument.h"
#include "cc/output/begin_frame_args.h"
namespace cc {
// Microclass to trace and check properties for correct BeginFrameArgs (BFA)
// usage and provide a few helper methods.
// With DCHECKs enable, this class checks the following "invariants";
// * BFA are monotonically increasing.
// * BFA is valid.
// * The BFA is only used inside a given period.
// * A new BFA isn't used before the last BFA is finished with.
// With the tracing category "cc.debug.scheduler.frames" enabled the tracker
// will output the following trace information;
// * Time period for which the BFA is in usage.
// * The flow of BFA as they are passed between tracking objects.
// TODO(mithro): Record stats about the BeginFrameArgs
class CC_EXPORT BeginFrameTracker {
explicit BeginFrameTracker(const tracked_objects::Location& location);
// The Start and Finish methods manage the period that a BFA should be
// accessed for. This allows tight control over the BFA and prevents
// accidental usage in the wrong period when code is split across multiple
// locations.
// Start using a new BFA value and check invariant properties.
// **Must** only be called after finishing with any previous BFA.
void Start(BeginFrameArgs new_args);
// Finish using the current BFA.
// **Must** only be called while still using a BFA.
void Finish();
// The two accessors methods allow access to the BFA stored inside the
// tracker. They are mutually exclusive, at any time it is only valid to call
// one or the other. This makes sure you understand exactly which BFA you are
// intending to use and verifies that is the case.
// Get the current BFA object.
// **Must** only be called between the start and finish methods calls.
const BeginFrameArgs& Current() const;
// Get the last used BFA.
// **Must** only be called when **not** between the start and finish method
// calls.
const BeginFrameArgs& Last() const;
// Helper method to try and return a valid interval property. Defaults to
// BFA::DefaultInterval() is no other interval can be found. Can be called at
// any time.
base::TimeDelta Interval() const;
void AsValueInto(base::TimeTicks now,
base::trace_event::TracedValue* dict) const;
// The following methods violate principles of how BeginFrameArgs should be
// used. These methods should only be used when there is no other choice.
bool DangerousMethodHasStarted() const {
return !current_updated_at_.is_null();
bool DangerousMethodHasFinished() const { return HasFinished(); }
const BeginFrameArgs& DangerousMethodCurrentOrLast() const;
// Return if currently not between the start/end period. This method should
// be used extremely sparingly and normal indicates incorrect management of
// the BFA object. Can be called at any time.
bool HasFinished() const { return !current_finished_at_.is_null(); }
const tracked_objects::Location location_;
const std::string location_string_;
base::TimeTicks current_updated_at_;
BeginFrameArgs current_args_;
base::TimeTicks current_finished_at_;
} // namespace cc