gecko/xpcom/ds/TimeStamp.h

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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla code.
*
* The Initial Developer of the Original Code is the Mozilla Corporation.
* Portions created by the Initial Developer are Copyright (C) 2009
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Robert O'Callahan <robert@ocallahan.org>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef mozilla_TimeStamp_h
#define mozilla_TimeStamp_h
#include "prinrval.h"
#include "nsDebug.h"
namespace mozilla {
class TimeStamp;
/**
* 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 PRInt64 in units of
* PR_TicksPerSecond().
*
* This whole class is inline so we don't need any special linkage.
*/
class TimeDuration {
public:
// The default duration is 0.
TimeDuration() : 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;
TimeDuration(_SomethingVeryRandomHere* aZero) : mValue(0) {
NS_ASSERTION(!aZero, "Who's playing funny games here?");
}
// Default copy-constructor and assignment are OK
double ToSeconds() const { return double(mValue)/PR_TicksPerSecond(); }
static TimeDuration FromSeconds(PRInt32 aSeconds) {
// No overflow is possible here
return TimeDuration::FromTicks(PRInt64(aSeconds)*PR_TicksPerSecond());
}
static TimeDuration FromMilliseconds(PRInt32 aMilliseconds) {
// No overflow is possible here
return TimeDuration::FromTicks(PRInt64(aMilliseconds)*PR_TicksPerSecond()/1000);
}
TimeDuration operator+(const TimeDuration& aOther) const {
return TimeDuration::FromTicks(mValue + aOther.mValue);
}
TimeDuration operator-(const TimeDuration& aOther) const {
return TimeDuration::FromTicks(mValue - aOther.mValue);
}
TimeDuration& operator+=(const TimeDuration& aOther) {
mValue += aOther.mValue;
return *this;
}
TimeDuration& operator-=(const TimeDuration& aOther) {
mValue -= aOther.mValue;
return *this;
}
PRBool operator<(const TimeDuration& aOther) const {
return mValue < aOther.mValue;
}
PRBool operator<=(const TimeDuration& aOther) const {
return mValue <= aOther.mValue;
}
PRBool operator>=(const TimeDuration& aOther) const {
return mValue >= aOther.mValue;
}
PRBool operator>(const TimeDuration& aOther) const {
return mValue > aOther.mValue;
}
// 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 should be discouraged.
private:
friend class TimeStamp;
static TimeDuration FromTicks(PRInt64 aTicks) {
TimeDuration t;
t.mValue = aTicks;
return t;
}
// Duration in PRIntervalTime units
PRInt64 mValue;
};
/**
* Instances of this class represent moments in time, or a special "null"
* moment. We do not use the 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 a wrapper around PRIntervalTime.
* We detect wraparounds of PRIntervalTime and work around them.
*/
class NS_COM TimeStamp {
public:
/**
* Initialize to the "null" moment
*/
TimeStamp() : mValue(0) {}
// Default copy-constructor and assignment are OK
/**
* Return true if this is the "null" moment
*/
PRBool IsNull() 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.
*/
static TimeStamp Now();
/**
* Compute the difference between two timestamps. Both must be non-null.
*/
TimeDuration operator-(const TimeStamp& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
return TimeDuration::FromTicks(mValue - aOther.mValue);
}
TimeStamp operator+(const TimeDuration& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
return TimeStamp(mValue + aOther.mValue);
}
TimeStamp operator-(const TimeDuration& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
return TimeStamp(mValue - aOther.mValue);
}
TimeStamp& operator+=(const TimeDuration& aOther) {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
mValue += aOther.mValue;
return *this;
}
TimeStamp& operator-=(const TimeDuration& aOther) {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
mValue -= aOther.mValue;
return *this;
}
PRBool operator<(const TimeStamp& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue < aOther.mValue;
}
PRBool operator<=(const TimeStamp& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue <= aOther.mValue;
}
PRBool operator>=(const TimeStamp& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue >= aOther.mValue;
}
PRBool operator>(const TimeStamp& aOther) const {
NS_ASSERTION(!IsNull(), "Cannot compute with a null value");
NS_ASSERTION(!aOther.IsNull(), "Cannot compute with aOther null value");
return mValue > aOther.mValue;
}
// Comparing TimeStamps for equality should be discouraged. Adding
// two TimeStamps, or scaling TimeStamps, is nonsense and must never
// be allowed.
static NS_HIDDEN_(nsresult) Startup();
static NS_HIDDEN_(void) Shutdown();
private:
TimeStamp(PRUint64 aValue) : mValue(aValue) {}
/**
* 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.
*/
PRUint64 mValue;
};
}
#endif /* mozilla_TimeStamp_h */