Source/WTF/wtf/MonotonicTime.h

/*
 * Copyright (C) 2016-2019 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#pragma once

#include <wtf/ClockType.h>
#include <wtf/GenericTimeMixin.h>

namespace WTF {

class WallTime;
class PrintStream;

// The current time according to a monotonic clock. Monotonic clocks don't go backwards and
// possibly don't count downtime. This uses floating point internally so that you can reason about
// infinity and other things that arise in math. It's acceptable to use this to wrap NaN times,
// negative times, and infinite times, so long as they are all relative to the same clock.
class MonotonicTime final : public GenericTimeMixin<MonotonicTime> {
public:
    static constexpr ClockType clockType = ClockType::Monotonic;
    
    // This is the epoch. So, x.secondsSinceEpoch() should be the same as x - MonotonicTime().
    constexpr MonotonicTime() = default;

#if OS(DARWIN)
    WTF_EXPORT_PRIVATE static MonotonicTime fromMachAbsoluteTime(uint64_t);
    WTF_EXPORT_PRIVATE uint64_t toMachAbsoluteTime() const;
#endif

    WTF_EXPORT_PRIVATE static MonotonicTime now();
    
    MonotonicTime approximateMonotonicTime() const { return *this; }
    WTF_EXPORT_PRIVATE WallTime approximateWallTime() const;

    WTF_EXPORT_PRIVATE void dump(PrintStream&) const;

    struct MarkableTraits;

private:
    friend class GenericTimeMixin<MonotonicTime>;
    constexpr MonotonicTime(double rawValue)
        : GenericTimeMixin<MonotonicTime>(rawValue)
    {
    }
};
static_assert(sizeof(MonotonicTime) == sizeof(double));

struct MonotonicTime::MarkableTraits {
    static bool isEmptyValue(MonotonicTime time)
    {
        return std::isnan(time.m_value);
    }

    static constexpr MonotonicTime emptyValue()
    {
        return MonotonicTime::nan();
    }
};

} // namespace WTF

namespace std {

inline bool isnan(WTF::MonotonicTime time)
{
    return std::isnan(time.secondsSinceEpoch().value());
}

inline bool isinf(WTF::MonotonicTime time)
{
    return std::isinf(time.secondsSinceEpoch().value());
}

inline bool isfinite(WTF::MonotonicTime time)
{
    return std::isfinite(time.secondsSinceEpoch().value());
}

} // namespace std

using WTF::MonotonicTime;