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// Copyright (c) 2011 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 "base/time/time.h"
#include "content/common/content_export.h"
namespace content {
class LocalTimeDelta;
class LocalTimeTicks;
class RemoteTimeDelta;
class RemoteTimeTicks;
// On Windows, TimeTicks are not consistent between processes. Often, the values
// on one process have a static offset relative to another. Occasionally, these
// offsets shift while running.
// To combat this, any TimeTicks values sent from the remote process to the
// local process must be tweaked in order to appear monotonic.
// In order to properly tweak ticks, we need 4 reference points:
// - |local_lower_bound|: A known point, recorded on the local process, that
// occurs before any remote values that will be
// converted.
// - |remote_lower_bound|: The equivalent point on the remote process. This
// should be recorded immediately after
// |local_lower_bound|.
// - |local_upper_bound|: A known point, recorded on the local process, that
// occurs after any remote values that will be
// converted.
// - |remote_upper_bound|: The equivalent point on the remote process. This
// should be recorded immediately before
// |local_upper_bound|.
// Once these bounds are determined, values within the remote process's range
// can be converted to the local process's range. The values are converted as
// follows:
// 1. If the remote's range exceeds the local's range, it is scaled to fit.
// Any values converted will have the same scale factor applied.
// 2. The remote's range is shifted so that it is centered within the
// local's range. Any values converted will be shifted the same amount.
class CONTENT_EXPORT InterProcessTimeTicksConverter {
InterProcessTimeTicksConverter(const LocalTimeTicks& local_lower_bound,
const LocalTimeTicks& local_upper_bound,
const RemoteTimeTicks& remote_lower_bound,
const RemoteTimeTicks& remote_upper_bound);
// Returns the value within the local's bounds that correlates to
// |remote_ms|.
LocalTimeTicks ToLocalTimeTicks(const RemoteTimeTicks& remote_ms) const;
// Returns the equivalent delta after applying remote-to-local scaling to
// |remote_delta|.
LocalTimeDelta ToLocalTimeDelta(const RemoteTimeDelta& remote_delta) const;
// Returns true iff the TimeTicks are converted by adding a constant, without
// scaling. This is the case whenever the remote timespan is smaller than the
// local timespan, which should be the majority of cases due to IPC overhead.
bool IsSkewAdditiveForMetrics() const;
// Returns the (remote time) - (local time) difference estimated by the
// converter. This is the constant that is subtracted from remote TimeTicks to
// get local TimeTicks when no scaling is applied.
base::TimeDelta GetSkewForMetrics() const;
int64 Convert(int64 value) const;
// The local time which |remote_lower_bound_| is mapped to.
int64 local_base_time_;
int64 numerator_;
int64 denominator_;
int64 remote_lower_bound_;
int64 remote_upper_bound_;
class CONTENT_EXPORT LocalTimeDelta {
int ToInt32() const { return value_; }
friend class InterProcessTimeTicksConverter;
friend class LocalTimeTicks;
LocalTimeDelta(int value) : value_(value) {}
int value_;
class CONTENT_EXPORT LocalTimeTicks {
static LocalTimeTicks FromTimeTicks(const base::TimeTicks& value) {
return LocalTimeTicks(value.ToInternalValue());
base::TimeTicks ToTimeTicks() {
return base::TimeTicks::FromInternalValue(value_);
LocalTimeTicks operator+(const LocalTimeDelta& delta) {
return LocalTimeTicks(value_ + delta.value_);
friend class InterProcessTimeTicksConverter;
LocalTimeTicks(int64 value) : value_(value) {}
int64 value_;
class CONTENT_EXPORT RemoteTimeDelta {
static RemoteTimeDelta FromRawDelta(int delta) {
return RemoteTimeDelta(delta);
friend class InterProcessTimeTicksConverter;
friend class RemoteTimeTicks;
RemoteTimeDelta(int value) : value_(value) {}
int value_;
class CONTENT_EXPORT RemoteTimeTicks {
static RemoteTimeTicks FromTimeTicks(const base::TimeTicks& ticks) {
return RemoteTimeTicks(ticks.ToInternalValue());
RemoteTimeDelta operator-(const RemoteTimeTicks& rhs) const {
return RemoteTimeDelta(value_ - rhs.value_);
friend class InterProcessTimeTicksConverter;
RemoteTimeTicks(int64 value) : value_(value) {}
int64 value_;
} // namespace content