chromium/third_party/blink/public/common/loader/inter_process_time_ticks_converter.h

// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_PUBLIC_COMMON_LOADER_INTER_PROCESS_TIME_TICKS_CONVERTER_H_
#define THIRD_PARTY_BLINK_PUBLIC_COMMON_LOADER_INTER_PROCESS_TIME_TICKS_CONVERTER_H_

#include <stdint.h>

#include "base/time/time.h"
#include "third_party/blink/public/common/common_export.h"

namespace blink {

// SiteSpecificTimeDelta<T> is base::TimeDelta with a type tag. It it
// essentially base::TimeDelta, but SiteSpecificTimeDelta<T> is different from
// SiteSpecificTimeDelta<U> if T is different from U.
template <typename T>
class SiteSpecificTimeDelta final { … };

// For logging use only.
template <typename T>
std::ostream& operator<<(std::ostream& os, SiteSpecificTimeDelta<T> delta) { … }

// SiteSpecificTimeTicks<T> is base::TimeTicks with a type tag. It is
// essentially base::TimeTicks, but SiteSpecificTimeTicks<T> is different from
// SiteSpecificTimeTicks<U> if T is different from U.
template <typename T>
class SiteSpecificTimeTicks final { … };

// For logging use only.
template <typename T>
std::ostream& operator<<(std::ostream& os,
                         SiteSpecificTimeTicks<T> time_ticks) { … }

class SiteSpecificTimeLocalTag;
LocalTimeTicks;
LocalTimeDelta;

class SiteSpecificTimeRemoteTag;
RemoteTimeTicks;
RemoteTimeDelta;

// On Windows, TimeTicks are not always consistent between processes as
// indicated by |TimeTicks::IsConsistentAcrossProcesses()|. 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 BLINK_COMMON_EXPORT InterProcessTimeTicksConverter { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_PUBLIC_COMMON_LOADER_INTER_PROCESS_TIME_TICKS_CONVERTER_H_