зеркало из https://github.com/mozilla/gecko-dev.git
304 строки
11 KiB
C++
304 строки
11 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Mozilla code.
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*
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* The Initial Developer of the Original Code is the Mozilla Corporation.
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Robert O'Callahan <robert@ocallahan.org>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#ifndef mozilla_TimeStamp_h
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#define mozilla_TimeStamp_h
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#include "prinrval.h"
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#include "nsDebug.h"
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#include "prlong.h"
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namespace mozilla {
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class TimeStamp;
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/**
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* Instances of this class represent the length of an interval of time.
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* Negative durations are allowed, meaning the end is before the start.
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*
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* Internally the duration is stored as a PRInt64 in units of
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* PR_TicksPerSecond() when building with NSPR interval timers, or a
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* system-dependent unit when building with system clocks. The
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* system-dependent unit must be constant, otherwise the semantics of
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* this class would be broken.
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*/
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class NS_COM TimeDuration
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{
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public:
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// The default duration is 0.
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TimeDuration() : mValue(0) {}
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// Allow construction using '0' as the initial value, for readability,
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// but no other numbers (so we don't have any implicit unit conversions).
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struct _SomethingVeryRandomHere;
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TimeDuration(_SomethingVeryRandomHere* aZero) : mValue(0) {
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NS_ASSERTION(!aZero, "Who's playing funny games here?");
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}
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// Default copy-constructor and assignment are OK
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double ToSeconds() const;
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// Return a duration value that includes digits of time we think to
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// be significant. This method should be used when displaying a
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// time to humans.
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double ToSecondsSigDigits() const;
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double ToMilliseconds() const {
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return ToSeconds() * 1000.0;
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}
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// Using a double here is safe enough; with 53 bits we can represent
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// durations up to over 280,000 years exactly. If the units of
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// mValue do not allow us to represent durations of that length,
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// long durations are clamped to the max/min representable value
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// instead of overflowing.
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static inline TimeDuration FromSeconds(double aSeconds) {
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return FromMilliseconds(aSeconds * 1000.0);
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}
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static TimeDuration FromMilliseconds(double aMilliseconds);
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TimeDuration operator+(const TimeDuration& aOther) const {
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return TimeDuration::FromTicks(mValue + aOther.mValue);
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}
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TimeDuration operator-(const TimeDuration& aOther) const {
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return TimeDuration::FromTicks(mValue - aOther.mValue);
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}
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TimeDuration& operator+=(const TimeDuration& aOther) {
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mValue += aOther.mValue;
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return *this;
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}
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TimeDuration& operator-=(const TimeDuration& aOther) {
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mValue -= aOther.mValue;
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return *this;
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}
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PRBool operator<(const TimeDuration& aOther) const {
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return mValue < aOther.mValue;
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}
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PRBool operator<=(const TimeDuration& aOther) const {
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return mValue <= aOther.mValue;
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}
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PRBool operator>=(const TimeDuration& aOther) const {
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return mValue >= aOther.mValue;
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}
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PRBool operator>(const TimeDuration& aOther) const {
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return mValue > aOther.mValue;
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}
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// Return a best guess at the system's current timing resolution,
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// which might be variable. TimeDurations below this order of
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// magnitude are meaningless, and those at the same order of
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// magnitude or just above are suspect.
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static TimeDuration Resolution();
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// We could define additional operators here:
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// -- convert to/from other time units
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// -- scale duration by a float
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// but let's do that on demand.
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// Comparing durations for equality will only lead to bugs on
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// platforms with high-resolution timers.
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private:
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friend class TimeStamp;
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static TimeDuration FromTicks(PRInt64 aTicks) {
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TimeDuration t;
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t.mValue = aTicks;
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return t;
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}
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static TimeDuration FromTicks(double aTicks) {
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// NOTE: this MUST be a >= test, because PRInt64(double(LL_MAXINT))
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// overflows and gives LL_MININT.
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if (aTicks >= double(LL_MAXINT))
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return TimeDuration::FromTicks(LL_MAXINT);
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// This MUST be a <= test.
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if (aTicks <= double(LL_MININT))
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return TimeDuration::FromTicks(LL_MININT);
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return TimeDuration::FromTicks(PRInt64(aTicks));
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}
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// Duration in PRIntervalTime units
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PRInt64 mValue;
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};
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/**
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* Instances of this class represent moments in time, or a special
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* "null" moment. We do not use the non-monotonic system clock or
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* local time, since they can be reset, causing apparent backward
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* travel in time, which can confuse algorithms. Instead we measure
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* elapsed time according to the system. This time can never go
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* backwards (i.e. it never wraps around, at least not in less than
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* five million years of system elapsed time). It might not advance
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* while the system is sleeping. If TimeStamp::SetNow() is not called
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* at all for hours or days, we might not notice the passage of some
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* of that time.
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*
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* We deliberately do not expose a way to convert TimeStamps to some
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* particular unit. All you can do is compute a difference between two
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* TimeStamps to get a TimeDuration. You can also add a TimeDuration
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* to a TimeStamp to get a new TimeStamp. You can't do something
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* meaningless like add two TimeStamps.
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*
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* Internally this is implemented as either a wrapper around
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* - high-resolution, monotonic, system clocks if they exist on this
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* platform
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* - PRIntervalTime otherwise. We detect wraparounds of
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* PRIntervalTime and work around them.
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*/
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class NS_COM TimeStamp
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{
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public:
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/**
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* Initialize to the "null" moment
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*/
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TimeStamp() : mValue(0) {}
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// Default copy-constructor and assignment are OK
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/**
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* Return true if this is the "null" moment
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*/
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PRBool IsNull() const { return mValue == 0; }
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/**
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* Return a timestamp reflecting the current elapsed system time. This
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* is monotonically increasing (i.e., does not decrease) over the
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* lifetime of this process' XPCOM session.
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*/
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static TimeStamp Now();
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/**
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* Compute the difference between two timestamps. Both must be non-null.
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*/
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TimeDuration operator-(const TimeStamp& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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PR_STATIC_ASSERT(-LL_MAXINT > LL_MININT);
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PRInt64 ticks = PRInt64(mValue - aOther.mValue);
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// Check for overflow.
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if (mValue > aOther.mValue) {
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if (ticks < 0) {
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ticks = LL_MAXINT;
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}
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} else {
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if (ticks > 0) {
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ticks = LL_MININT;
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}
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}
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return TimeDuration::FromTicks(ticks);
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}
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TimeStamp operator+(const TimeDuration& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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return TimeStamp(mValue + aOther.mValue);
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}
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TimeStamp operator-(const TimeDuration& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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return TimeStamp(mValue - aOther.mValue);
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}
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TimeStamp& operator+=(const TimeDuration& aOther) {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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mValue += aOther.mValue;
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return *this;
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}
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TimeStamp& operator-=(const TimeDuration& aOther) {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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mValue -= aOther.mValue;
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return *this;
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}
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PRBool operator<(const TimeStamp& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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return mValue < aOther.mValue;
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}
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PRBool operator<=(const TimeStamp& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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return mValue <= aOther.mValue;
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}
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PRBool operator>=(const TimeStamp& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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return mValue >= aOther.mValue;
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}
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PRBool operator>(const TimeStamp& aOther) const {
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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return mValue > aOther.mValue;
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}
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PRBool operator==(const TimeStamp& aOther) const {
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// Maybe it's ok to check == with null timestamps?
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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return mValue == aOther.mValue;
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}
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PRBool operator!=(const TimeStamp& aOther) const {
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// Maybe it's ok to check != with null timestamps?
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NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
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NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
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return mValue != aOther.mValue;
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}
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// Comparing TimeStamps for equality should be discouraged. Adding
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// two TimeStamps, or scaling TimeStamps, is nonsense and must never
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// be allowed.
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static NS_HIDDEN_(nsresult) Startup();
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static NS_HIDDEN_(void) Shutdown();
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private:
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TimeStamp(PRUint64 aValue) : mValue(aValue) {}
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/**
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* When built with PRIntervalTime, a value of 0 means this instance
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* is "null". Otherwise, the low 32 bits represent a PRIntervalTime,
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* and the high 32 bits represent a counter of the number of
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* rollovers of PRIntervalTime that we've seen. This counter starts
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* at 1 to avoid a real time colliding with the "null" value.
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*
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* PR_INTERVAL_MAX is set at 100,000 ticks per second. So the minimum
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* time to wrap around is about 2^64/100000 seconds, i.e. about
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* 5,849,424 years.
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*
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* When using a system clock, a value is system dependent.
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*/
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PRUint64 mValue;
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};
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}
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#endif /* mozilla_TimeStamp_h */
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