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ACE_High_Res_Timer Class Reference

A high resolution timer class wrapper that encapsulates OS-specific high-resolution timers, such as those found on Solaris, AIX, Win32/Pentium, and VxWorks. More...

#include <High_Res_Timer.h>

Public Types

typedef ACE_UINT64 global_scale_factor_type

Public Member Functions

 ACE_High_Res_Timer (void)
 Initialize the timer. More...
 ~ACE_High_Res_Timer (void)
 Destructor. More...
void reset (void)
 Reinitialize the timer. More...
void start (const ACE_OS::ACE_HRTimer_Op=ACE_OS::ACE_HRTIMER_GETTIME)
 Start timing. More...
void stop (const ACE_OS::ACE_HRTimer_Op=ACE_OS::ACE_HRTIMER_GETTIME)
 Stop timing. More...
void elapsed_time (ACE_Time_Value &tv) const
 Set tv to the number of microseconds elapsed. More...
void elapsed_time (ACE_hrtime_t &nanoseconds) const
 Set nanoseconds to the number of nanoseconds elapsed. More...
void elapsed_microseconds (ACE_hrtime_t &usecs) const
 Sets usecs to the elapsed (stop - start) time in microseconds. More...
void start_incr (const ACE_OS::ACE_HRTimer_Op=ACE_OS::ACE_HRTIMER_GETTIME)
 Start incremental timing. More...
void stop_incr (const ACE_OS::ACE_HRTimer_Op=ACE_OS::ACE_HRTIMER_GETTIME)
 Stop incremental timing. More...
void elapsed_time_incr (ACE_Time_Value &tv) const
void elapsed_time_incr (ACE_hrtime_t &nanoseconds) const
void print_total (const ACE_TCHAR *message, const int iterations=1, ACE_HANDLE handle=ACE_STDOUT) const
void print_ave (const ACE_TCHAR *message, const int iterations=1, ACE_HANDLE handle=ACE_STDOUT) const
 Print average time. More...
void dump (void) const
 Dump the state of an object. More...

Static Public Member Functions

static void global_scale_factor (global_scale_factor_type gsf)
static global_scale_factor_type global_scale_factor (void)
 Returns the global_scale_factor. More...
static int get_env_global_scale_factor (const ACE_TCHAR *env=ACE_TEXT("ACE_SCALE_FACTOR"))
static ACE_UINT32 calibrate (const ACE_UINT32 usec=500000, const u_int iterations=10)
static ACE_Time_Value gettimeofday_hr (void)
static ACE_Time_Value gettimeofday (const ACE_OS::ACE_HRTimer_Op=ACE_OS::ACE_HRTIMER_GETTIME)
static void hrtime_to_tv (ACE_Time_Value &tv, const ACE_hrtime_t hrt)
 Converts an hrt to tv using global_scale_factor_. More...

Public Attributes

 Declare the dynamic allocation hooks. More...

Static Private Member Functions

static ACE_hrtime_t gettime (const ACE_OS::ACE_HRTimer_Op=ACE_OS::ACE_HRTIMER_GETTIME)
static ACE_hrtime_t elapsed_hrtime (const ACE_hrtime_t end, const ACE_hrtime_t start)

Private Attributes

ACE_hrtime_t start_
 Starting time. More...
ACE_hrtime_t end_
 Ending time. More...
ACE_hrtime_t total_
 Total elapsed time. More...
ACE_hrtime_t start_incr_
 Start time of incremental timing. More...

Static Private Attributes

static global_scale_factor_type global_scale_factor_ = 1u
static int global_scale_factor_status_ = 0

Detailed Description

A high resolution timer class wrapper that encapsulates OS-specific high-resolution timers, such as those found on Solaris, AIX, Win32/Pentium, and VxWorks.

Most of the member functions don't return values. The only reason that one would fail is if high-resolution time isn't supported on the platform. To avoid impacting performance and complicating the interface, in that case, <ACE_OS::gettimeofday> is used instead. The global scale factor is required for platforms that have high-resolution timers that return units other than microseconds, such as clock ticks. It is represented as a static u_long, can only be accessed through static methods, and is used by all instances of High Res Timer. The member functions that return or print times use the global scale factor. They divide the "time" that they get from <ACE_OS::gethrtime> by global_scale_factor_ to obtain the time in microseconds. Its units are therefore 1/microsecond. On Windows the global_scale_factor_ units are 1/millisecond. There's a macro <ACE_HR_SCALE_CONVERSION> which gives the units/second. Because it's possible that the units/second changes in the future, it's recommended to use it instead of a "hard coded" solution. Dependent on the platform and used class members, there's a maximum elapsed period before overflow (which is not checked). Look at the documentation with some members functions. On some (most?) implementations it's not recommended to measure "long" timeperiods, because the error's can accumulate fast. This is probably not a problem profiling code, but could be on if the high resolution timer class is used to initiate actions after a "long" timeout. On Solaris, a scale factor of 1000 should be used because its high-resolution timer returns nanoseconds. However, on Intel platforms, we use RDTSC which returns the number of clock ticks since system boot. For a 200MHz cpu, each clock tick is 1/200 of a microsecond; the global_scale_factor_ should therefore be 200 or 200000 if it's in unit/millisecond. On Windows ::QueryPerformanceCounter() is used, which can be a different implementation depending on the used windows HAL (Hardware Abstraction Layer). On some it uses the PC "timer chip" while it uses RDTSC on others.

The elapsed time calculations in the print methods use ACE_hrtime_t values. Those methods do not check for overflow!
Gabe raises this issue regarding <ACE_OS::gethrtime>: on multi-processors, the processor that you query for your timer.stop() value might not be the one you queried for timer.start(). Its not clear how much divergence there would be, if any. This issue is not mentioned in the Solaris 2.5.1 gethrtime man page. A RDTSC NOTE: RDTSC is the Intel Pentium read-time stamp counter and is actualy a 64 bit clock cycle counter, which is increased with every cycle. It has a low overhead and can be read within 16 (pentium) or 32 (pentium II,III,...) cycles, but it doesn't serialize the processor, which could give wrong timings when profiling very short code fragments. Problematic is that some power sensitive devices (laptops for example, but probably also embedded devices), do change the cycle rate while running. Some pentiums can run on (at least) two clock frequency's. Another problem arises with multiprocessor computers, there are reports that the different RDTSC's are not always kept in sync. A windows "timer chip" NOTE: (8254-compatible real-time clock) When ::QueryPerformanceCounter() uses the 8254 it has a frequency off about 1.193 Mhz (or sometimes 3.579 Mhz?) and reading it requires some time (several thousand cycles).

Member Typedef Documentation

Constructor & Destructor Documentation

ACE_High_Res_Timer::ACE_High_Res_Timer ( void  )

Initialize the timer.

ACE_High_Res_Timer::~ACE_High_Res_Timer ( void  )


Member Function Documentation

ACE_UINT32 ACE_High_Res_Timer::calibrate ( const ACE_UINT32  usec = 500000,
const u_int  iterations = 10 

Set (and return, for info) the global scale factor by sleeping for usec and counting the number of intervening clock cycles. Average over iterations of usec each. On some platforms, such as Pentiums, this is called automatically during the first ACE_High_Res_Timer construction with the default parameter values. An application can override that by calling calibrate with any desired parameter values prior to constructing the first ACE_High_Res_Timer instance. Beware for platforms that can change the cycle rate on the fly.

void ACE_High_Res_Timer::dump ( void  ) const

Dump the state of an object.

ACE_hrtime_t ACE_High_Res_Timer::elapsed_hrtime ( const ACE_hrtime_t  end,
const ACE_hrtime_t  start 

Calculate the difference between two ACE_hrtime_t values. It is assumed that the end time is later than start time, so if end is a smaller value, the time counter has wrapped around.

void ACE_High_Res_Timer::elapsed_microseconds ( ACE_hrtime_t usecs) const

Sets usecs to the elapsed (stop - start) time in microseconds.

Will overflow on windows when measuring more than appox. 2^^54 ticks. Is still more than 48 days with a 4 Ghz counter.

void ACE_High_Res_Timer::elapsed_time ( ACE_Time_Value tv) const

Set tv to the number of microseconds elapsed.

void ACE_High_Res_Timer::elapsed_time ( ACE_hrtime_t nanoseconds) const

Set nanoseconds to the number of nanoseconds elapsed.

Will overflow when measuring more than 194 day's.

void ACE_High_Res_Timer::elapsed_time_incr ( ACE_Time_Value tv) const

Set tv to the number of microseconds elapsed between all calls to start_incr and stop_incr.

void ACE_High_Res_Timer::elapsed_time_incr ( ACE_hrtime_t nanoseconds) const

Set nanoseconds to the number of nanoseconds elapsed between all calls to start_incr and stop_incr.

int ACE_High_Res_Timer::get_env_global_scale_factor ( const ACE_TCHAR env = ACE_TEXT ("ACE_SCALE_FACTOR"))

Sets the global_scale_factor to the value in the env environment variable. Returns 0 on success, -1 on failure.

If env points to string "0" (value zero), this call will fail. This is basically a no-op on CE because there is no concept of environment variable on CE.
ACE_hrtime_t ACE_High_Res_Timer::gettime ( const ACE_OS::ACE_HRTimer_Op  op = ACE_OS::ACE_HRTIMER_GETTIME)

For internal use: gets the high-resolution time using <ACE_OS::gethrtime>. Except on platforms that require that the <global_scale_factor_> be set, such as ACE_WIN32, uses the low-resolution clock if the <global_scale_factor_> has not been set.

ACE_Time_Value ACE_High_Res_Timer::gettimeofday ( const ACE_OS::ACE_HRTimer_Op  op = ACE_OS::ACE_HRTIMER_GETTIME)
THIS FUNCTION IS DEPRECATED. PLEASE USE <ACE_OS::gettimeofday> INSTEAD! Calls <ACE_High_Res_Timer::hrtime_to_tv> passing <ACE_OS::gethrtime>. This function can be used to parameterize objects such as <ACE_Timer_Queue::gettimeofday>. If <global_scale_factor_> is not set, and we're on a platform that requires <global_scale_factor_> (e.g., Win32), ACE_OS::gettimeofday will be used instead of <ACE_OS::gethrtime>. This allows applications on Intel to use <High_Res_Timer> even when <global_scale_factor> is not set. However, setting the <global_scale_factor_> appropriately will result in the finest resolution possible.
ACE_Time_Value ACE_High_Res_Timer::gettimeofday_hr ( void  )

Get the current "time" as the high resolution counter at this time. This is intended to be useful for supplying to a ACE_Timer_Queue as the gettimeofday function, thereby basing the timer calculations on the high res timer rather than wall clock time.

Get the current high res timer as the time of day. This is intended to be used for a gettimeofday replacement in ACE_Timer_Queue and derived classes so the timers will be based on high res timers rather than wall clock time. It uses the ACE_High_Res_Timer::gettimeofday function, which is deprecated. If it gets removed, please move the code down here, intact.

void ACE_High_Res_Timer::global_scale_factor ( ACE_High_Res_Timer::global_scale_factor_type  gsf)

global_scale_factor_ is set to gsf. All High_Res_Timers use global_scale_factor_. This allows applications to set the scale factor just once for all High_Res_Timers. Check High_Res_Timer.cpp for the default global_scale_factors for several platforms. For many platforms (e.g., Solaris), the global_scale_factor_ is set to 1000 so that <scale_factor> need not be set. Careful, a <scale_factor> of 0 will cause division by zero exceptions. Depending on the platform its units are 1/microsecond or 1/millisecond. Use ACE_HR_SCALE_CONVERSION inside calculations instead a hardcoded value.

ACE_High_Res_Timer::global_scale_factor_type ACE_High_Res_Timer::global_scale_factor ( void  )

Returns the global_scale_factor.

void ACE_High_Res_Timer::hrtime_to_tv ( ACE_Time_Value tv,
const ACE_hrtime_t  hrt 

Converts an hrt to tv using global_scale_factor_.

Be very careful before changing the calculations inside ACE_High_Res_Timer. The precision matters and we are using integer calculations not floating point.

void ACE_High_Res_Timer::print_ave ( const ACE_TCHAR message,
const int  iterations = 1,
) const

Print average time.

void ACE_High_Res_Timer::print_total ( const ACE_TCHAR message,
const int  iterations = 1,
) const

Print total time.

only use print_total if incremental timings had been used!
void ACE_High_Res_Timer::reset ( void  )

Reinitialize the timer.

void ACE_High_Res_Timer::start ( const ACE_OS::ACE_HRTimer_Op  op = ACE_OS::ACE_HRTIMER_GETTIME)

Start timing.

void ACE_High_Res_Timer::start_incr ( const ACE_OS::ACE_HRTimer_Op  op = ACE_OS::ACE_HRTIMER_GETTIME)

Start incremental timing.

void ACE_High_Res_Timer::stop ( const ACE_OS::ACE_HRTimer_Op  op = ACE_OS::ACE_HRTIMER_GETTIME)

Stop timing.

void ACE_High_Res_Timer::stop_incr ( const ACE_OS::ACE_HRTimer_Op  op = ACE_OS::ACE_HRTIMER_GETTIME)

Stop incremental timing.

Member Data Documentation


Declare the dynamic allocation hooks.

ACE_hrtime_t ACE_High_Res_Timer::end_

Ending time.

ACE_High_Res_Timer::global_scale_factor_type ACE_High_Res_Timer::global_scale_factor_ = 1u

Converts ticks to microseconds. That is, ticks / global_scale_factor_ == microseconds.

Initialize the global_scale_factor_ to 1. The first ACE_High_Res_Timer instance construction will override this value.

int ACE_High_Res_Timer::global_scale_factor_status_ = 0

Indicates the status of the global scale factor, 0 = hasn't been set 1 = been set -1 = HR timer not supported

This is used to tell if the global_scale_factor_ has been set, and if high resolution timers are supported.

ACE_hrtime_t ACE_High_Res_Timer::start_

Starting time.

ACE_hrtime_t ACE_High_Res_Timer::start_incr_

Start time of incremental timing.

ACE_hrtime_t ACE_High_Res_Timer::total_

Total elapsed time.

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