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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_TimeStamp_h
#define mozilla_TimeStamp_h
#include <stdint.h>
#include <algorithm> // for std::min, std::max
#include <ostream>
#include <type_traits>
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/Types.h"
namespace IPC {
template <typename T>
struct ParamTraits;
} // namespace IPC
#ifdef XP_WIN
// defines TimeStampValue as a complex value keeping both
// GetTickCount and QueryPerformanceCounter values
# include "TimeStamp_windows.h"
#endif
namespace mozilla {
#ifndef XP_WIN
typedef uint64_t TimeStampValue;
#endif
class TimeStamp;
/**
* Platform-specific implementation details of BaseTimeDuration.
*/
class BaseTimeDurationPlatformUtils {
public:
static MFBT_API double ToSeconds(int64_t aTicks);
static MFBT_API double ToSecondsSigDigits(int64_t aTicks);
static MFBT_API int64_t TicksFromMilliseconds(double aMilliseconds);
static MFBT_API int64_t ResolutionInTicks();
};
/**
* Instances of this class represent the length of an interval of time.
* Negative durations are allowed, meaning the end is before the start.
*
* Internally the duration is stored as a int64_t in units of
* PR_TicksPerSecond() when building with NSPR interval timers, or a
* system-dependent unit when building with system clocks. The
* system-dependent unit must be constant, otherwise the semantics of
* this class would be broken.
*
* The ValueCalculator template parameter determines how arithmetic
* operations are performed on the integer count of ticks (mValue).
*/
template <typename ValueCalculator>
class BaseTimeDuration {
public:
// The default duration is 0.
constexpr BaseTimeDuration() : mValue(0) {}
// Allow construction using '0' as the initial value, for readability,
// but no other numbers (so we don't have any implicit unit conversions).
struct _SomethingVeryRandomHere;
MOZ_IMPLICIT BaseTimeDuration(_SomethingVeryRandomHere* aZero) : mValue(0) {
MOZ_ASSERT(!aZero, "Who's playing funny games here?");
}
// Default copy-constructor and assignment are OK
// Converting copy-constructor and assignment operator
template <typename E>
explicit BaseTimeDuration(const BaseTimeDuration<E>& aOther)
: mValue(aOther.mValue) {}
template <typename E>
BaseTimeDuration& operator=(const BaseTimeDuration<E>& aOther) {
mValue = aOther.mValue;
return *this;
}
double ToSeconds() const {
if (mValue == INT64_MAX) {
return PositiveInfinity<double>();
}
if (mValue == INT64_MIN) {
return NegativeInfinity<double>();
}
return BaseTimeDurationPlatformUtils::ToSeconds(mValue);
}
// Return a duration value that includes digits of time we think to
// be significant. This method should be used when displaying a
// time to humans.
double ToSecondsSigDigits() const {
if (mValue == INT64_MAX) {
return PositiveInfinity<double>();
}
if (mValue == INT64_MIN) {
return NegativeInfinity<double>();
}
return BaseTimeDurationPlatformUtils::ToSecondsSigDigits(mValue);
}
double ToMilliseconds() const { return ToSeconds() * 1000.0; }
double ToMicroseconds() const { return ToMilliseconds() * 1000.0; }
// Using a double here is safe enough; with 53 bits we can represent
// durations up to over 280,000 years exactly. If the units of
// mValue do not allow us to represent durations of that length,
// long durations are clamped to the max/min representable value
// instead of overflowing.
static inline BaseTimeDuration FromSeconds(double aSeconds) {
return FromMilliseconds(aSeconds * 1000.0);
}
static BaseTimeDuration FromMilliseconds(double aMilliseconds) {
if (aMilliseconds == PositiveInfinity<double>()) {
return Forever();
}
if (aMilliseconds == NegativeInfinity<double>()) {
return FromTicks(INT64_MIN);
}
return FromTicks(
BaseTimeDurationPlatformUtils::TicksFromMilliseconds(aMilliseconds));
}
static inline BaseTimeDuration FromMicroseconds(double aMicroseconds) {
return FromMilliseconds(aMicroseconds / 1000.0);
}
static constexpr BaseTimeDuration Forever() { return FromTicks(INT64_MAX); }
BaseTimeDuration operator+(const BaseTimeDuration& aOther) const {
return FromTicks(ValueCalculator::Add(mValue, aOther.mValue));
}
BaseTimeDuration operator-(const BaseTimeDuration& aOther) const {
return FromTicks(ValueCalculator::Subtract(mValue, aOther.mValue));
}
BaseTimeDuration& operator+=(const BaseTimeDuration& aOther) {
mValue = ValueCalculator::Add(mValue, aOther.mValue);
return *this;
}
BaseTimeDuration& operator-=(const BaseTimeDuration& aOther) {
mValue = ValueCalculator::Subtract(mValue, aOther.mValue);
return *this;
}
BaseTimeDuration operator-() const {
// We don't just use FromTicks(ValueCalculator::Subtract(0, mValue))
// since that won't give the correct result for -TimeDuration::Forever().
int64_t ticks;
if (mValue == INT64_MAX) {
ticks = INT64_MIN;
} else if (mValue == INT64_MIN) {
ticks = INT64_MAX;
} else {
ticks = -mValue;
}
return FromTicks(ticks);
}
static BaseTimeDuration Max(const BaseTimeDuration& aA,
const BaseTimeDuration& aB) {
return FromTicks(std::max(aA.mValue, aB.mValue));
}
static BaseTimeDuration Min(const BaseTimeDuration& aA,
const BaseTimeDuration& aB) {
return FromTicks(std::min(aA.mValue, aB.mValue));
}
private:
// Block double multiplier (slower, imprecise if long duration) - Bug 853398.
// If required, use MultDouble explicitly and with care.
BaseTimeDuration operator*(const double aMultiplier) const = delete;
// Block double divisor (for the same reason, and because dividing by
// fractional values would otherwise invoke the int64_t variant, and rounding
// the passed argument can then cause divide-by-zero) - Bug 1147491.
BaseTimeDuration operator/(const double aDivisor) const = delete;
public:
BaseTimeDuration MultDouble(double aMultiplier) const {
return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));
}
BaseTimeDuration operator*(const int32_t aMultiplier) const {
return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));
}
BaseTimeDuration operator*(const uint32_t aMultiplier) const {
return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));
}
BaseTimeDuration operator*(const int64_t aMultiplier) const {
return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));
}
BaseTimeDuration operator*(const uint64_t aMultiplier) const {
if (aMultiplier > INT64_MAX) {
return Forever();
}
return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));
}
BaseTimeDuration operator/(const int64_t aDivisor) const {
MOZ_ASSERT(aDivisor != 0, "Division by zero");
return FromTicks(ValueCalculator::Divide(mValue, aDivisor));
}
double operator/(const BaseTimeDuration& aOther) const {
MOZ_ASSERT(aOther.mValue != 0, "Division by zero");
return ValueCalculator::DivideDouble(mValue, aOther.mValue);
}
BaseTimeDuration operator%(const BaseTimeDuration& aOther) const {
MOZ_ASSERT(aOther.mValue != 0, "Division by zero");
return FromTicks(ValueCalculator::Modulo(mValue, aOther.mValue));
}
template <typename E>
bool operator<(const BaseTimeDuration<E>& aOther) const {
return mValue < aOther.mValue;
}
template <typename E>
bool operator<=(const BaseTimeDuration<E>& aOther) const {
return mValue <= aOther.mValue;
}
template <typename E>
bool operator>=(const BaseTimeDuration<E>& aOther) const {
return mValue >= aOther.mValue;
}
template <typename E>
bool operator>(const BaseTimeDuration<E>& aOther) const {
return mValue > aOther.mValue;
}
template <typename E>
bool operator==(const BaseTimeDuration<E>& aOther) const {
return mValue == aOther.mValue;
}
template <typename E>
bool operator!=(const BaseTimeDuration<E>& aOther) const {
return mValue != aOther.mValue;
}
bool IsZero() const { return mValue == 0; }
explicit operator bool() const { return mValue != 0; }
friend std::ostream& operator<<(std::ostream& aStream,
const BaseTimeDuration& aDuration) {
return aStream << aDuration.ToMilliseconds() << " ms";
}
// Return a best guess at the system's current timing resolution,
// which might be variable. BaseTimeDurations below this order of
// magnitude are meaningless, and those at the same order of
// magnitude or just above are suspect.
static BaseTimeDuration Resolution() {
return FromTicks(BaseTimeDurationPlatformUtils::ResolutionInTicks());
}
// We could define additional operators here:
// -- convert to/from other time units
// -- scale duration by a float
// but let's do that on demand.
// Comparing durations for equality will only lead to bugs on
// platforms with high-resolution timers.
private:
friend class TimeStamp;
friend struct IPC::ParamTraits<mozilla::BaseTimeDuration<ValueCalculator>>;
template <typename>
friend class BaseTimeDuration;
static BaseTimeDuration FromTicks(int64_t aTicks) {
BaseTimeDuration t;
t.mValue = aTicks;
return t;
}
static BaseTimeDuration FromTicks(double aTicks) {
// NOTE: this MUST be a >= test, because int64_t(double(INT64_MAX))
// overflows and gives INT64_MIN.
if (aTicks >= double(INT64_MAX)) {
return FromTicks(INT64_MAX);
}
// This MUST be a <= test.
if (aTicks <= double(INT64_MIN)) {
return FromTicks(INT64_MIN);
}
return FromTicks(int64_t(aTicks));
}
// Duration, result is implementation-specific difference of two TimeStamps
int64_t mValue;
};
/**
* Perform arithmetic operations on the value of a BaseTimeDuration without
* doing strict checks on the range of values.
*/
class TimeDurationValueCalculator {
public:
static int64_t Add(int64_t aA, int64_t aB) { return aA + aB; }
static int64_t Subtract(int64_t aA, int64_t aB) { return aA - aB; }
template <typename T>
static int64_t Multiply(int64_t aA, T aB) {
static_assert(std::is_integral_v<T>,
"Using integer multiplication routine with non-integer type."
" Further specialization required");
return aA * static_cast<int64_t>(aB);
}
static int64_t Divide(int64_t aA, int64_t aB) { return aA / aB; }
static double DivideDouble(int64_t aA, int64_t aB) {
return static_cast<double>(aA) / aB;
}
static int64_t Modulo(int64_t aA, int64_t aB) { return aA % aB; }
};
template <>
inline int64_t TimeDurationValueCalculator::Multiply<double>(int64_t aA,
double aB) {
return static_cast<int64_t>(aA * aB);
}
/**
* Specialization of BaseTimeDuration that uses TimeDurationValueCalculator for
* arithmetic on the mValue member.
*
* Use this class for time durations that are *not* expected to hold values of
* Forever (or the negative equivalent) or when such time duration are *not*
* expected to be used in arithmetic operations.
*/
typedef BaseTimeDuration<TimeDurationValueCalculator> TimeDuration;
/**
* Instances of this class represent moments in time, or a special
* "null" moment. We do not use the non-monotonic system clock or
* local time, since they can be reset, causing apparent backward
* travel in time, which can confuse algorithms. Instead we measure
* elapsed time according to the system. This time can never go
* backwards (i.e. it never wraps around, at least not in less than
* five million years of system elapsed time). It might not advance
* while the system is sleeping. If TimeStamp::SetNow() is not called
* at all for hours or days, we might not notice the passage of some
* of that time.
*
* We deliberately do not expose a way to convert TimeStamps to some
* particular unit. All you can do is compute a difference between two
* TimeStamps to get a TimeDuration. You can also add a TimeDuration
* to a TimeStamp to get a new TimeStamp. You can't do something
* meaningless like add two TimeStamps.
*
* Internally this is implemented as either a wrapper around
* - high-resolution, monotonic, system clocks if they exist on this
* platform
* - PRIntervalTime otherwise. We detect wraparounds of
* PRIntervalTime and work around them.
*
* This class is similar to C++11's time_point, however it is
* explicitly nullable and provides an IsNull() method. time_point
* is initialized to the clock's epoch and provides a
* time_since_epoch() method that functions similiarly. i.e.
* t.IsNull() is equivalent to t.time_since_epoch() ==
* decltype(t)::duration::zero();
*
* Note that, since TimeStamp objects are small, prefer to pass them by value
* unless there is a specific reason not to do so.
*/
class TimeStamp {
public:
/**
* Initialize to the "null" moment
*/
constexpr TimeStamp() : mValue(0) {}
// Default copy-constructor and assignment are OK
/**
* The system timestamps are the same as the TimeStamp
* retrieved by mozilla::TimeStamp. Since we need this for
* vsync timestamps, we enable the creation of mozilla::TimeStamps
* on platforms that support vsync aligned refresh drivers / compositors
* Verified true as of Jan 31, 2015: B2G and OS X
* False on Windows 7
* Android's event time uses CLOCK_MONOTONIC via SystemClock.uptimeMilles.
* So it is same value of TimeStamp posix implementation.
* Wayland/GTK event time also uses CLOCK_MONOTONIC on Weston/Mutter
* compositors.
* UNTESTED ON OTHER PLATFORMS
*/
#if defined(XP_DARWIN) || defined(MOZ_WIDGET_ANDROID) || defined(MOZ_WIDGET_GTK)
static TimeStamp FromSystemTime(int64_t aSystemTime) {
static_assert(sizeof(aSystemTime) == sizeof(TimeStampValue),
"System timestamp should be same units as TimeStampValue");
return TimeStamp(aSystemTime);
}
#endif
/**
* Return true if this is the "null" moment
*/
bool IsNull() const { return mValue == 0; }
/**
* Return true if this is not the "null" moment, may be used in tests, e.g.:
* |if (timestamp) { ... }|
*/
explicit operator bool() const { return mValue != 0; }
/**
* Return a timestamp reflecting the current elapsed system time. This
* is monotonically increasing (i.e., does not decrease) over the
* lifetime of this process' XPCOM session.
*
* Now() is trying to ensure the best possible precision on each platform,
* at least one millisecond.
*
* NowLoRes() has been introduced to workaround performance problems of
* QueryPerformanceCounter on the Windows platform. NowLoRes() is giving
* lower precision, usually 15.6 ms, but with very good performance benefit.
* Use it for measurements of longer times, like >200ms timeouts.
*/
static TimeStamp Now() { return Now(true); }
static TimeStamp NowLoRes() { return Now(false); }
/**
* Return a timestamp representing the time when the current process was
* created which will be comparable with other timestamps taken with this
* class. If the actual process creation time is detected to be inconsistent
* the @a aIsInconsistent parameter will be set to true, the returned
* timestamp however will still be valid though inaccurate.
*
* @param aIsInconsistent If non-null, set to true if an inconsistency was
* detected in the process creation time
* @returns A timestamp representing the time when the process was created,
* this timestamp is always valid even when errors are reported
*/
static MFBT_API TimeStamp ProcessCreation(bool* aIsInconsistent = nullptr);
/**
* Records a process restart. After this call ProcessCreation() will return
* the time when the browser was restarted instead of the actual time when
* the process was created.
*/
static MFBT_API void RecordProcessRestart();
/**
* Compute the difference between two timestamps. Both must be non-null.
*/
TimeDuration operator-(const TimeStamp& aOther) const {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
static_assert(-INT64_MAX > INT64_MIN, "int64_t sanity check");
int64_t ticks = int64_t(mValue - aOther.mValue);
// Check for overflow.
if (mValue > aOther.mValue) {
if (ticks < 0) {
ticks = INT64_MAX;
}
} else {
if (ticks > 0) {
ticks = INT64_MIN;
}
}
return TimeDuration::FromTicks(ticks);
}
TimeStamp operator+(const TimeDuration& aOther) const {
TimeStamp result = *this;
result += aOther;
return result;
}
TimeStamp operator-(const TimeDuration& aOther) const {
TimeStamp result = *this;
result -= aOther;
return result;
}
TimeStamp& operator+=(const TimeDuration& aOther) {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
TimeStampValue value = mValue + aOther.mValue;
// Check for underflow.
// (We don't check for overflow because it's not obvious what the error
// behavior should be in that case.)
if (aOther.mValue < 0 && value > mValue) {
value = 0;
}
mValue = value;
return *this;
}
TimeStamp& operator-=(const TimeDuration& aOther) {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
TimeStampValue value = mValue - aOther.mValue;
// Check for underflow.
// (We don't check for overflow because it's not obvious what the error
// behavior should be in that case.)
if (aOther.mValue > 0 && value > mValue) {
value = 0;
}
mValue = value;
return *this;
}
bool operator<(const TimeStamp& aOther) const {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue < aOther.mValue;
}
bool operator<=(const TimeStamp& aOther) const {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue <= aOther.mValue;
}
bool operator>=(const TimeStamp& aOther) const {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue >= aOther.mValue;
}
bool operator>(const TimeStamp& aOther) const {
MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue > aOther.mValue;
}
bool operator==(const TimeStamp& aOther) const {
return IsNull() ? aOther.IsNull()
: !aOther.IsNull() && mValue == aOther.mValue;
}
bool operator!=(const TimeStamp& aOther) const { return !(*this == aOther); }
// Comparing TimeStamps for equality should be discouraged. Adding
// two TimeStamps, or scaling TimeStamps, is nonsense and must never
// be allowed.
static MFBT_API void Startup();
static MFBT_API void Shutdown();
private:
friend struct IPC::ParamTraits<mozilla::TimeStamp>;
MOZ_IMPLICIT TimeStamp(TimeStampValue aValue) : mValue(aValue) {}
static MFBT_API TimeStamp Now(bool aHighResolution);
/**
* Computes the uptime of the current process in microseconds. The result
* is platform-dependent and needs to be checked against existing timestamps
* for consistency.
*
* @returns The number of microseconds since the calling process was started
* or 0 if an error was encountered while computing the uptime
*/
static MFBT_API uint64_t ComputeProcessUptime();
/**
* When built with PRIntervalTime, a value of 0 means this instance
* is "null". Otherwise, the low 32 bits represent a PRIntervalTime,
* and the high 32 bits represent a counter of the number of
* rollovers of PRIntervalTime that we've seen. This counter starts
* at 1 to avoid a real time colliding with the "null" value.
*
* PR_INTERVAL_MAX is set at 100,000 ticks per second. So the minimum
* time to wrap around is about 2^64/100000 seconds, i.e. about
* 5,849,424 years.
*
* When using a system clock, a value is system dependent.
*/
TimeStampValue mValue;
};
} // namespace mozilla
#endif /* mozilla_TimeStamp_h */