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lat::TimeInfo Class Reference

Utilities for monotonically growing high-resolution timers. More...

#include <Iguana/Utilities/classlib/utils/TimeInfo.h>

List of all members.

Public Types
typedef double	NanoSecs
	Type for nanosecond times.
typedef IntBits< 64 >::SLeast	NanoTicks
	Type for cpu cycle counters.
Static Public Member Functions
static NanoSecs	elapsedTime (void)
static unsigned	features ()
static double	ghz (void)
static void	init (void)
static double	mhz (void)
static void	msleep (NanoSecs msecs)
static void	nanosleep (NanoSecs nanosecs)
static NanoSecs	processCpuTime (void)
static NanoSecs	processIdleTime (void)
static NanoSecs	processRealTime (void)
static NanoSecs	processSystemTime (void)
static void	processTimes (NanoSecs &user, NanoSecs &system, NanoSecs &real)
static NanoSecs	processUserTime (void)
static NanoTicks	realCycles (void)
static NanoSecs	realNsecs (void)
static NanoSecs	resolution (void)
static void	sleep (NanoSecs secs)
static NanoSecs	time (void)
static void	usleep (NanoSecs usecs)
static NanoTicks	virtualCycles (void)
static NanoSecs	virtualNsecs (void)
Static Public Attributes
static const int	FEATURE_EXACT_MHZ = 1
	feature() bit indicating that mhz() is the exact value provided by the system (for the cycle counts vs.
static const int	FEATURE_PROCESS_TIMES = 16
	feature() bit indicating that processUserTime(), processSystemTime() and processCpuTime() are meaningful.
static const int	FEATURE_REAL_COUNT_EPOCH = 4
	feature() bit indicating that realCycles() and realNsecs() can have have system-wide source.
static const int	FEATURE_TIME_EPOCH = 2
	feature() bit indicating that time() may not be process-specific but can have system-wide source.
Static Private Member Functions
static void	spin (NanoSecs duration, NanoTicks &low, NanoTicks &high)
Static Private Attributes
static NanoSecs	s_clockBase
static unsigned	s_features
static double	s_ghz
static double	s_hiResFactor
static bool	s_initialised

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Detailed Description

Utilities for monotonically growing high-resolution timers.

This class provides access to, among other things, virtual and real nanosecond-resolution timing info. The implementation does its best to use the cheapest, most trustworthy time calculation method: system-provided high-resolution clocks or reading CPU cycle counters directly. If those are not available, falls back to whatever is likely to produce the best data on the system, usually a system call that promises best resolution.

On systems that do provide accurate monotonic process-specific or system-wide high-resolution clocks (e.g. POSIX CLOCK_MONOTONIC and CLOCK_PROCESS_CPUTIME_ID clocks), they are used in preference to CPU cycle counters. If no such clock is available, the monotonicity cannot always be guaranteed:

• On a SMP system the process may hop from one processor to another, reading cycle counters on different CPUs.
• Most multi-processor systems allow CPUs to be taken offline and put back online at any time. The cycle counters may be reset or slowed down while the processor is offline.
• Advanced power saving features can slow down CPU clock rates or put processes or the whole system to sleep or suspend mode. In such a case the returned cycle counts may still be accurate but cannot be converted to nanoseconds meaningfully. At any rate it is usually impossible to find out when this has happened. In fact the clock speed reported by the system may not even be right if something (e.g. the user) has put the system in a power-conserving mode that has slowed down the CPU clock rate -- the CPU clock rate may be wrong for the whole duration of the program.

In most of these cases it is anybody's guess what the timers read after such an event. Most likely the readings are not linear.

The clock ticks are represented as a 64-bit signed integral type (see NanoTicks). Nanosecond times are represented as a double (see NanoSecs). This accomodates some 290 years worth of cycle counter ticks on a 1GHz CPU. Cycle counters are usually zeroed on boot, so this should be plenty enough for another few years to come. Please note however that not all systems provide cycle counters with this many significant bits.

Definition at line 57 of file TimeInfo.h.

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Member Typedef Documentation

typedef double lat::TimeInfo::NanoSecs

Type for nanosecond times.

Definition at line 89 of file TimeInfo.h.

typedef IntBits<64>::SLeast lat::TimeInfo::NanoTicks

Type for cpu cycle counters.

Definition at line 92 of file TimeInfo.h.

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Member Function Documentation

static NanoSecs lat::TimeInfo::elapsedTime

(

void

)

[static]

static unsigned lat::TimeInfo::features

(

)

[static]

static double lat::TimeInfo::ghz

(

void

)

[static]

static void lat::TimeInfo::init

(

void

)

[static]

Referenced by IgApplication::run().

static double lat::TimeInfo::mhz

(

void

)

[static]

static void lat::TimeInfo::msleep

(

NanoSecs

msecs

)

[static]

static void lat::TimeInfo::nanosleep

(

NanoSecs

nanosecs

)

[static]

static NanoSecs lat::TimeInfo::processCpuTime

(

void

)

[static]

static NanoSecs lat::TimeInfo::processIdleTime

(

void

)

[static]

Referenced by IgApplication::run().

static NanoSecs lat::TimeInfo::processRealTime

(

void

)

[static]

Referenced by IgApplication::run().

static NanoSecs lat::TimeInfo::processSystemTime

(

void

)

[static]

Referenced by IgApplication::run().

static void lat::TimeInfo::processTimes	(	NanoSecs &	user,
		NanoSecs &	system,
		NanoSecs &	real
	)			[static]

static NanoSecs lat::TimeInfo::processUserTime

(

void

)

[static]

Referenced by IgApplication::run().

static NanoTicks lat::TimeInfo::realCycles

(

void

)

[static]

static NanoSecs lat::TimeInfo::realNsecs

(

void

)

[static]

static NanoSecs lat::TimeInfo::resolution

(

void

)

[static]

static void lat::TimeInfo::sleep

(

NanoSecs

secs

)

[static]

static void lat::TimeInfo::spin	(	NanoSecs	duration,
		NanoTicks &	low,
		NanoTicks &	high
	)			[static, private]

static NanoSecs lat::TimeInfo::time

(

void

)

[static]

static void lat::TimeInfo::usleep

(

NanoSecs

usecs

)

[static]

static NanoTicks lat::TimeInfo::virtualCycles

(

void

)

[static]

static NanoSecs lat::TimeInfo::virtualNsecs

(

void

)

[static]

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Member Data Documentation

const int lat::TimeInfo::FEATURE_EXACT_MHZ = 1 [static]

feature() bit indicating that mhz() is the exact value provided by the system (for the cycle counts vs.

nsecs). If not set, the speed was estimated with a calibration loop.

Definition at line 73 of file TimeInfo.h.

const int lat::TimeInfo::FEATURE_PROCESS_TIMES = 16 [static]

feature() bit indicating that processUserTime(), processSystemTime() and processCpuTime() are meaningful.

Definition at line 86 of file TimeInfo.h.

const int lat::TimeInfo::FEATURE_REAL_COUNT_EPOCH = 4 [static]

feature() bit indicating that realCycles() and realNsecs() can have have system-wide source.

Definition at line 81 of file TimeInfo.h.

const int lat::TimeInfo::FEATURE_TIME_EPOCH = 2 [static]

feature() bit indicating that time() may not be process-specific but can have system-wide source.

Definition at line 77 of file TimeInfo.h.

NanoSecs lat::TimeInfo::s_clockBase [static, private]

Definition at line 144 of file TimeInfo.h.

unsigned lat::TimeInfo::s_features [static, private]

Definition at line 141 of file TimeInfo.h.

double lat::TimeInfo::s_ghz [static, private]

Definition at line 142 of file TimeInfo.h.

double lat::TimeInfo::s_hiResFactor [static, private]

Definition at line 143 of file TimeInfo.h.

bool lat::TimeInfo::s_initialised [static, private]

Definition at line 140 of file TimeInfo.h.

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The documentation for this class was generated from the following file:

• Iguana/Utilities/classlib/utils/TimeInfo.h

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