I have the code sample bellow to measure the execution time of some piece of code:
int main()
{
auto before = chrono::steady_clock::now();
Sleep(30000);
auto after = chrono::steady_clock::now();
int duration = (std::chrono::duration_cast<std::chrono::seconds> ((after - before)).count());
cout << duration << endl;
return 0;
}
Normally it works fine and prints out 30 in the cout statement.
However, during testing I observed that if the computer were to go to sleep in between the auto before = ... statement and the auto after = ... statement (due to inactivity or whatever other reason), then the printed out time also counts the entire time the machine was asleep. This makes perfect sense since we are comparing a timepoint from before the machine going to sleep and one with after.
So my question is how can I make it so that the duration the machine was asleep is not counted in my final duration? Probably will need a ticker that doesn't increment while machine is asleep rather than timepoint measurements but I'm not aware of such a ticker.
This is a Windows specific question. As I understand, MacOS has mach_absolute_time which is exactly what I'm looking for in windows. I'm using MSVC 19.29.30147.0 as my compiler.
After looking around and testing it out, the solution is to use QueryUnbiasedInterruptTime
Running the following code snippet, I manually put my machine to sleep while the program was stuck on the sleep statement and I observed that the second print out consistently outputs 15 seconds regardless of how long I leave my machine in a sleeping state. However, the first print-out that uses GetTickCount64 will include the amount of time the machine was asleep.
int main()
{
ULONGLONG before_query, after_query= 0;
QueryUnbiasedInterruptTime(&before_query);
auto beforeticks = GetTickCount64();
Sleep(15000);
QueryUnbiasedInterruptTime(&after_query);
auto afterticks = GetTickCount64();
cout << "Ticks from gettickcount64 is " << (double (afterticks-beforeticks))/1000 << endl;
cout << "Unbiased time measure is " << double((after_query - before_query)/10000000) << endl;
return 0;
}
You are correct that the easiest way is to use a counter that is incremented each second. This is easily implemented with threads:
#include <thread>
#include <atomic>
#include <chrono>
using namespace std::literals::chrono_literals;
class ellapsed_counter {
std::atomic<bool> finished = false;
std::atomic<unsigned int> value = 0;
std::thread worker { [this] {
while(!finished) {
value++;
std::this_thread::sleep_for(1s);
}
} };
public:
void finish() noexcept {
finished = true;
if(worker.joinable()) worker.join();
}
unsigned int ellapsed() const noexcept { return value; }
};
This will keep incrementing on 1s intervals (probably with some error) as long as the process is running and should cease so when it is sleeping.
You can use it like this:
#include <iostream>
int main(int argc, const char *argv[]) {
ellapsed_counter counter;
unsigned int last = 0, count = 0;
while(count < 10) {
count = counter.ellapsed();
if(count != last) {
last = count;
std::cout << count << std::endl;
}
}
counter.finish();
return 0;
}
This will count from 1 to 10 seconds and exit.
I want to find out how much time a certain function takes in my C++ program to execute on Linux. Afterwards, I want to make a speed comparison . I saw several time function but ended up with this from boost. Chrono:
process_user_cpu_clock, captures user-CPU time spent by the current process
Now, I am not clear if I use the above function, will I get the only time which CPU spent on that function?
Secondly, I could not find any example of using the above function. Can any one please help me how to use the above function?
P.S: Right now , I am using std::chrono::system_clock::now() to get time in seconds but this gives me different results due to different CPU load every time.
It is a very easy-to-use method in C++11. You have to use std::chrono::high_resolution_clock from <chrono> header.
Use it like so:
#include <chrono>
/* Only needed for the sake of this example. */
#include <iostream>
#include <thread>
void long_operation()
{
/* Simulating a long, heavy operation. */
using namespace std::chrono_literals;
std::this_thread::sleep_for(150ms);
}
int main()
{
using std::chrono::high_resolution_clock;
using std::chrono::duration_cast;
using std::chrono::duration;
using std::chrono::milliseconds;
auto t1 = high_resolution_clock::now();
long_operation();
auto t2 = high_resolution_clock::now();
/* Getting number of milliseconds as an integer. */
auto ms_int = duration_cast<milliseconds>(t2 - t1);
/* Getting number of milliseconds as a double. */
duration<double, std::milli> ms_double = t2 - t1;
std::cout << ms_int.count() << "ms\n";
std::cout << ms_double.count() << "ms\n";
return 0;
}
This will measure the duration of the function long_operation.
Possible output:
150ms
150.068ms
Working example: https://godbolt.org/z/oe5cMd
Here's a function that will measure the execution time of any function passed as argument:
#include <chrono>
#include <utility>
typedef std::chrono::high_resolution_clock::time_point TimeVar;
#define duration(a) std::chrono::duration_cast<std::chrono::nanoseconds>(a).count()
#define timeNow() std::chrono::high_resolution_clock::now()
template<typename F, typename... Args>
double funcTime(F func, Args&&... args){
TimeVar t1=timeNow();
func(std::forward<Args>(args)...);
return duration(timeNow()-t1);
}
Example usage:
#include <iostream>
#include <algorithm>
typedef std::string String;
//first test function doing something
int countCharInString(String s, char delim){
int count=0;
String::size_type pos = s.find_first_of(delim);
while ((pos = s.find_first_of(delim, pos)) != String::npos){
count++;pos++;
}
return count;
}
//second test function doing the same thing in different way
int countWithAlgorithm(String s, char delim){
return std::count(s.begin(),s.end(),delim);
}
int main(){
std::cout<<"norm: "<<funcTime(countCharInString,"precision=10",'=')<<"\n";
std::cout<<"algo: "<<funcTime(countWithAlgorithm,"precision=10",'=');
return 0;
}
Output:
norm: 15555
algo: 2976
In Scott Meyers book I found an example of universal generic lambda expression that can be used to measure function execution time. (C++14)
auto timeFuncInvocation =
[](auto&& func, auto&&... params) {
// get time before function invocation
const auto& start = std::chrono::high_resolution_clock::now();
// function invocation using perfect forwarding
std::forward<decltype(func)>(func)(std::forward<decltype(params)>(params)...);
// get time after function invocation
const auto& stop = std::chrono::high_resolution_clock::now();
return stop - start;
};
The problem is that you are measure only one execution so the results can be very differ. To get a reliable result you should measure a large number of execution.
According to Andrei Alexandrescu lecture at code::dive 2015 conference - Writing Fast Code I:
Measured time: tm = t + tq + tn + to
where:
tm - measured (observed) time
t - the actual time of interest
tq - time added by quantization noise
tn - time added by various sources of noise
to - overhead time (measuring, looping, calling functions)
According to what he said later in the lecture, you should take a minimum of this large number of execution as your result.
I encourage you to look at the lecture in which he explains why.
Also there is a very good library from google - https://github.com/google/benchmark.
This library is very simple to use and powerful. You can checkout some lectures of Chandler Carruth on youtube where he is using this library in practice. For example CppCon 2017: Chandler Carruth “Going Nowhere Faster”;
Example usage:
#include <iostream>
#include <chrono>
#include <vector>
auto timeFuncInvocation =
[](auto&& func, auto&&... params) {
// get time before function invocation
const auto& start = high_resolution_clock::now();
// function invocation using perfect forwarding
for(auto i = 0; i < 100000/*largeNumber*/; ++i) {
std::forward<decltype(func)>(func)(std::forward<decltype(params)>(params)...);
}
// get time after function invocation
const auto& stop = high_resolution_clock::now();
return (stop - start)/100000/*largeNumber*/;
};
void f(std::vector<int>& vec) {
vec.push_back(1);
}
void f2(std::vector<int>& vec) {
vec.emplace_back(1);
}
int main()
{
std::vector<int> vec;
std::vector<int> vec2;
std::cout << timeFuncInvocation(f, vec).count() << std::endl;
std::cout << timeFuncInvocation(f2, vec2).count() << std::endl;
std::vector<int> vec3;
vec3.reserve(100000);
std::vector<int> vec4;
vec4.reserve(100000);
std::cout << timeFuncInvocation(f, vec3).count() << std::endl;
std::cout << timeFuncInvocation(f2, vec4).count() << std::endl;
return 0;
}
EDIT:
Ofcourse you always need to remember that your compiler can optimize something out or not. Tools like perf can be useful in such cases.
simple program to find a function execution time taken.
#include <iostream>
#include <ctime> // time_t
#include <cstdio>
void function()
{
for(long int i=0;i<1000000000;i++)
{
// do nothing
}
}
int main()
{
time_t begin,end; // time_t is a datatype to store time values.
time (&begin); // note time before execution
function();
time (&end); // note time after execution
double difference = difftime (end,begin);
printf ("time taken for function() %.2lf seconds.\n", difference );
return 0;
}
Easy way for older C++, or C:
#include <time.h> // includes clock_t and CLOCKS_PER_SEC
int main() {
clock_t start, end;
start = clock();
// ...code to measure...
end = clock();
double duration_sec = double(end-start)/CLOCKS_PER_SEC;
return 0;
}
Timing precision in seconds is 1.0/CLOCKS_PER_SEC
#include <iostream>
#include <chrono>
void function()
{
// code here;
}
int main()
{
auto t1 = std::chrono::high_resolution_clock::now();
function();
auto t2 = std::chrono::high_resolution_clock::now();
auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
std::cout << duration<<"/n";
return 0;
}
This Worked for me.
Note:
The high_resolution_clock is not implemented consistently across different standard library implementations, and its use should be avoided. It is often just an alias for std::chrono::steady_clock or std::chrono::system_clock, but which one it is depends on the library or configuration. When it is a system_clock, it is not monotonic (e.g., the time can go backwards).
For example, for gcc's libstdc++ it is system_clock, for MSVC it is steady_clock, and for clang's libc++ it depends on configuration.
Generally one should just use std::chrono::steady_clock or std::chrono::system_clock directly instead of std::chrono::high_resolution_clock: use steady_clock for duration measurements, and system_clock for wall-clock time.
Here is an excellent header only class template to measure the elapsed time of a function or any code block:
#ifndef EXECUTION_TIMER_H
#define EXECUTION_TIMER_H
template<class Resolution = std::chrono::milliseconds>
class ExecutionTimer {
public:
using Clock = std::conditional_t<std::chrono::high_resolution_clock::is_steady,
std::chrono::high_resolution_clock,
std::chrono::steady_clock>;
private:
const Clock::time_point mStart = Clock::now();
public:
ExecutionTimer() = default;
~ExecutionTimer() {
const auto end = Clock::now();
std::ostringstream strStream;
strStream << "Destructor Elapsed: "
<< std::chrono::duration_cast<Resolution>( end - mStart ).count()
<< std::endl;
std::cout << strStream.str() << std::endl;
}
inline void stop() {
const auto end = Clock::now();
std::ostringstream strStream;
strStream << "Stop Elapsed: "
<< std::chrono::duration_cast<Resolution>(end - mStart).count()
<< std::endl;
std::cout << strStream.str() << std::endl;
}
}; // ExecutionTimer
#endif // EXECUTION_TIMER_H
Here are some uses of it:
int main() {
{ // empty scope to display ExecutionTimer's destructor's message
// displayed in milliseconds
ExecutionTimer<std::chrono::milliseconds> timer;
// function or code block here
timer.stop();
}
{ // same as above
ExecutionTimer<std::chrono::microseconds> timer;
// code block here...
timer.stop();
}
{ // same as above
ExecutionTimer<std::chrono::nanoseconds> timer;
// code block here...
timer.stop();
}
{ // same as above
ExecutionTimer<std::chrono::seconds> timer;
// code block here...
timer.stop();
}
return 0;
}
Since the class is a template we can specify real easily in how we want our time to be measured & displayed. This is a very handy utility class template for doing bench marking and is very easy to use.
If you want to safe time and lines of code you can make measuring the function execution time a one line macro:
a) Implement a time measuring class as already suggested above ( here is my implementation for android):
class MeasureExecutionTime{
private:
const std::chrono::steady_clock::time_point begin;
const std::string caller;
public:
MeasureExecutionTime(const std::string& caller):caller(caller),begin(std::chrono::steady_clock::now()){}
~MeasureExecutionTime(){
const auto duration=std::chrono::steady_clock::now()-begin;
LOGD("ExecutionTime")<<"For "<<caller<<" is "<<std::chrono::duration_cast<std::chrono::milliseconds>(duration).count()<<"ms";
}
};
b) Add a convenient macro that uses the current function name as TAG (using a macro here is important, else __FUNCTION__ will evaluate to MeasureExecutionTime instead of the function you wanto to measure
#ifndef MEASURE_FUNCTION_EXECUTION_TIME
#define MEASURE_FUNCTION_EXECUTION_TIME const MeasureExecutionTime measureExecutionTime(__FUNCTION__);
#endif
c) Write your macro at the begin of the function you want to measure. Example:
void DecodeMJPEGtoANativeWindowBuffer(uvc_frame_t* frame_mjpeg,const ANativeWindow_Buffer& nativeWindowBuffer){
MEASURE_FUNCTION_EXECUTION_TIME
// Do some time-critical stuff
}
Which will result int the following output:
ExecutionTime: For DecodeMJPEGtoANativeWindowBuffer is 54ms
Note that this (as all other suggested solutions) will measure the time between when your function was called and when it returned, not neccesarily the time your CPU was executing the function. However, if you don't give the scheduler any change to suspend your running code by calling sleep() or similar there is no difference between.
It is a very easy to use method in C++11.
We can use std::chrono::high_resolution_clock from header
We can write a method to print the method execution time in a much readable form.
For example, to find the all the prime numbers between 1 and 100 million, it takes approximately 1 minute and 40 seconds.
So the execution time get printed as:
Execution Time: 1 Minutes, 40 Seconds, 715 MicroSeconds, 715000 NanoSeconds
The code is here:
#include <iostream>
#include <chrono>
using namespace std;
using namespace std::chrono;
typedef high_resolution_clock Clock;
typedef Clock::time_point ClockTime;
void findPrime(long n, string file);
void printExecutionTime(ClockTime start_time, ClockTime end_time);
int main()
{
long n = long(1E+8); // N = 100 million
ClockTime start_time = Clock::now();
// Write all the prime numbers from 1 to N to the file "prime.txt"
findPrime(n, "C:\\prime.txt");
ClockTime end_time = Clock::now();
printExecutionTime(start_time, end_time);
}
void printExecutionTime(ClockTime start_time, ClockTime end_time)
{
auto execution_time_ns = duration_cast<nanoseconds>(end_time - start_time).count();
auto execution_time_ms = duration_cast<microseconds>(end_time - start_time).count();
auto execution_time_sec = duration_cast<seconds>(end_time - start_time).count();
auto execution_time_min = duration_cast<minutes>(end_time - start_time).count();
auto execution_time_hour = duration_cast<hours>(end_time - start_time).count();
cout << "\nExecution Time: ";
if(execution_time_hour > 0)
cout << "" << execution_time_hour << " Hours, ";
if(execution_time_min > 0)
cout << "" << execution_time_min % 60 << " Minutes, ";
if(execution_time_sec > 0)
cout << "" << execution_time_sec % 60 << " Seconds, ";
if(execution_time_ms > 0)
cout << "" << execution_time_ms % long(1E+3) << " MicroSeconds, ";
if(execution_time_ns > 0)
cout << "" << execution_time_ns % long(1E+6) << " NanoSeconds, ";
}
I recommend using steady_clock which is guarunteed to be monotonic, unlike high_resolution_clock.
#include <iostream>
#include <chrono>
using namespace std;
unsigned int stopwatch()
{
static auto start_time = chrono::steady_clock::now();
auto end_time = chrono::steady_clock::now();
auto delta = chrono::duration_cast<chrono::microseconds>(end_time - start_time);
start_time = end_time;
return delta.count();
}
int main() {
stopwatch(); //Start stopwatch
std::cout << "Hello World!\n";
cout << stopwatch() << endl; //Time to execute last line
for (int i=0; i<1000000; i++)
string s = "ASDFAD";
cout << stopwatch() << endl; //Time to execute for loop
}
Output:
Hello World!
62
163514
Since none of the provided answers are very accurate or give reproducable results I decided to add a link to my code that has sub-nanosecond precision and scientific statistics.
Note that this will only work to measure code that takes a (very) short time to run (aka, a few clock cycles to a few thousand): if they run so long that they are likely to be interrupted by some -heh- interrupt, then it is clearly not possible to give a reproducable and accurate result; the consequence of which is that the measurement never finishes: namely, it continues to measure until it is statistically 99.9% sure it has the right answer which never happens on a machine that has other processes running when the code takes too long.
https://github.com/CarloWood/cwds/blob/master/benchmark.h#L40
You can have a simple class which can be used for this kind of measurements.
class duration_printer {
public:
duration_printer() : __start(std::chrono::high_resolution_clock::now()) {}
~duration_printer() {
using namespace std::chrono;
high_resolution_clock::time_point end = high_resolution_clock::now();
duration<double> dur = duration_cast<duration<double>>(end - __start);
std::cout << dur.count() << " seconds" << std::endl;
}
private:
std::chrono::high_resolution_clock::time_point __start;
};
The only thing is needed to do is to create an object in your function at the beginning of that function
void veryLongExecutingFunction() {
duration_calculator dc;
for(int i = 0; i < 100000; ++i) std::cout << "Hello world" << std::endl;
}
int main() {
veryLongExecutingFunction();
return 0;
}
and that's it. The class can be modified to fit your requirements.
C++11 cleaned up version of Jahid's response:
#include <chrono>
#include <thread>
void long_operation(int ms)
{
/* Simulating a long, heavy operation. */
std::this_thread::sleep_for(std::chrono::milliseconds(ms));
}
template<typename F, typename... Args>
double funcTime(F func, Args&&... args){
std::chrono::high_resolution_clock::time_point t1 =
std::chrono::high_resolution_clock::now();
func(std::forward<Args>(args)...);
return std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::high_resolution_clock::now()-t1).count();
}
int main()
{
std::cout<<"expect 150: "<<funcTime(long_operation,150)<<"\n";
return 0;
}
This is a very basic timer class which you can expand on depending on your needs. I wanted something straightforward which can be used cleanly in code. You can mess with it at coding ground with this link: http://tpcg.io/nd47hFqr.
class local_timer {
private:
std::chrono::_V2::system_clock::time_point start_time;
std::chrono::_V2::system_clock::time_point stop_time;
std::chrono::_V2::system_clock::time_point stop_time_temp;
std::chrono::microseconds most_recent_duration_usec_chrono;
double most_recent_duration_sec;
public:
local_timer() {
};
~local_timer() {
};
void start() {
this->start_time = std::chrono::high_resolution_clock::now();
};
void stop() {
this->stop_time = std::chrono::high_resolution_clock::now();
};
double get_time_now() {
this->stop_time_temp = std::chrono::high_resolution_clock::now();
this->most_recent_duration_usec_chrono = std::chrono::duration_cast<std::chrono::microseconds>(stop_time_temp-start_time);
this->most_recent_duration_sec = (long double)most_recent_duration_usec_chrono.count()/1000000;
return this->most_recent_duration_sec;
};
double get_duration() {
this->most_recent_duration_usec_chrono = std::chrono::duration_cast<std::chrono::microseconds>(stop_time-start_time);
this->most_recent_duration_sec = (long double)most_recent_duration_usec_chrono.count()/1000000;
return this->most_recent_duration_sec;
};
};
The use for this being
#include <iostream>
#include "timer.hpp" //if kept in an hpp file in the same folder, can also before your main function
int main() {
//create two timers
local_timer timer1 = local_timer();
local_timer timer2 = local_timer();
//set start time for timer1
timer1.start();
//wait 1 second
while(timer1.get_time_now() < 1.0) {
}
//save time
timer1.stop();
//print time
std::cout << timer1.get_duration() << " seconds, timer 1\n" << std::endl;
timer2.start();
for(long int i = 0; i < 100000000; i++) {
//do something
if(i%1000000 == 0) {
//return time since loop started
std::cout << timer2.get_time_now() << " seconds, timer 2\n"<< std::endl;
}
}
return 0;
}
I'm trying to make a loading screen for a simulation I have to do, so the console isn't just blank for 10 seconds. I just want to add an asterisk to a line every 2 seconds of simulation time. Here's the code for I came up with for the loading screen.
#include <iostream>
#include <cstdlib>
#include <ctime>
int main()
{
//initialize a random seed
srand(time(NULL));
time_t simTime=10;
time_t passedTime=0;
time_t beginTime=time(NULL);
do
{
time_t currentTime=time(NULL);
passedTime=currentTime-beginTime;
//Code for simulation
if(passedTime%2==0)
cout<<"*";
cout<<endl;
}while(passedTime<simTime);
It just prints out asterisks neverendingly for 10 seconds.
You implemented active waiting. You will need two threads: One that does the loading and one that mostly sleeps and prints the asterisc every two seconds or so. Maybe something like this:
bool loadingComplete;
void PrintLoading()
{
do
{
std::cout << '*';
std::this_thread::sleep_for(2s);
}
while(!loadingComplete);
}
void LoadStuff()
{
// Long running task
}
int main()
{
std::thread t(PrintLoading);
loadingComplete = false;
LoadStuff();
loadingComplete = true;
t.join();
}
Without actively interrupting the thread this might run 2 seconds longer than needed and I didn't have time to test, but I hope it points you in the right direction.
You don't necessarily need a separate thread if you simply want to print out the asterisks while you do your similation in your loop.
Here's an example based on your code:
#include <chrono>
#include <iostream>
using namespace std;
int main() {
float simulation_duration = 0.0;
float maximum_duration = 10.0;
auto time_since_start_or_last_asterisk = chrono::high_resolution_clock::now();
do {
//Code for simulation
auto current_time = chrono::high_resolution_clock::now();
std::chrono::duration<double> time_since_last_asterisk = current_time - time_since_start_or_last_asterisk;
if (time_since_last_asterisk.count() >= 2.0){
cout << "*";
cout.flush();
simulation_duration += time_since_last_asterisk.count();
time_since_start_or_last_asterisk = current_time;
}
} while (simulation_duration < maximum_duration);
cout << endl;
}
I am trying to make a basic keylogger, and I want to be able to close the program after 20 minutes. looking online I found this clock_T functions, but I can't figure out how to transform this into seconds (and from seconds I will be able to make mins).
I tried to use the good old timer based on the "sleep" function.
but it gave me a huge amount of problems considering that I must be able to type anytime and save it in a log.
I am not able to understand high level of coding, therefore I struggled quite a bit looking at videos or descriptions on the internet.
I was expecting to see displayed the seconds increasing over time, so I would later on be able to shut down the code once the desired amount of second would be reached, but I instead ran into a spam of the same number for the specific second.
example: 1111111111111111111111111111111111 (after one second it increases)22222222222222222222222222222222 (increases again) 333333333333333333333333. and so on.
#include <iostream>
#include <string>
#include <Windows.h>
#include <fstream>
#include <time.h>
using namespace std;
int main() {
// FreeConsole();
clock_t start = 0;
clock_t end = 0;
clock_t delta = 0;
start = clock();
fstream info;
string filename = "Data.txt";
while (true) {
info.open(filename.c_str(), ios::app);
for (char i = 31; i < 122; i++) {
if (GetAsyncKeyState(i) == -32767) {
info << i;
cout << i;
}
}
info.close();
end = clock();
delta = end - start;
delta = delta; // 1000;
std::cout << delta/CLOCKS_PER_SEC << endl;
}
return 0;
}
I have this class template that uses the chrono library. Here is a simple example of its use.
main.cpp
#include <iostream>
#include "Timer.h"
int main() {
while( Timer<minutes>(1).isRunning() ) {
// do something for 1 minute
}
while ( Timer<seconds>(30).isRunning() ) {
// do something for 30 seconds
}
return 0;
}
Timer.h
#pragma once
#include <chrono>
using namespace std::chrono;
template<class Resolution = seconds>
class Timer {
public:
using Clock = std::conditional_t<high_resolution_clock::is_steady,
high_resolution_clock, steady_clock>;
private:
Clock::time_point startTime_;
Clock::time_point timeToRunFor_;
bool isRunning_ = false;
public:
explicit Timer(int count) :
startTime_{ Clock::now() },
timeToRunFor_{ Clock::now() + Resolution(count) },
isRunning_{ true }
{
run();
}
~Timer() {
const auto stopTime = Clock::now();
std::ostringstream stream;
stream << "Time Elapsed: "
<< duration_cast<Resolution>(stopTime - startTime_).count()
<< std::endl;
std::cout << stream.str() << std::endl;
}
bool isRunning() {
return isRunning_;
}
private:
void run() {
while (steady_clock::now() < timeToRunFor_) {}
isRunning_ = false;
}
};
Output
Time Elapsed: 1
Time Elapsed: 30
Time waited for first about 1 minute then printed 1, then waited for about 30 seconds then printed 30. This is a nice light weight class and is simple to use.
I'm currently in the process of adding more to this class to give support for manual starting and stopping usages with a default constructor. As this class currently stands above you could create an instance or an object of this class as a variable, and give it a time explicitly and it will run for that long, but you can not manually start and stop this timer when you want to. Once I finish this class, the default constructor will not use the internal members timeToRunFor_ and run() as they are meant to be used with the explicit constructor version.
Once completed you can set how long you want something to run for via the while loop then terminate after desired time has expired via the Explicit constructor version, or you can create a local instance of this class as an object, invoke the start function, do some other operations for and unknown amount of time, then call the stop function after and perform the query of the time elapsed. I need a little more time to finish this class so I will post this as is for now and once I complete my updates to the class I'll update it here to the newer version!
I try to make sure the execution time of each loop to 10ms with usleep , but sometimes it exceeds 10ms.
I have no idea how to solve this problem, is it proper to use usleep and gettimeofday in this case?
Please help my find out what i missed.
Result: 0.0127289
0.0136499
0.0151598
0.0114031
0.014801
double tvsecf(){
struct timeval tv;
double asec;
gettimeofday(&tv,NULL);
asec = tv.tv_usec;
asec /= 1e6;
asec += tv.tv_sec;
return asec;
}
int main(){
double t1 ,t2;
t1 = tvsecf();
for(;;){
t2= tvsecf();
if(t2-t1 >= 0.01){
if(t2-t1 >= 0.011)
cout << t2-t1 <<endl;
t1 = tvsecf();
}
usleep(100);
}
}
To keep the loop overhead (which is generally unknown) from constantly accumulating error, you can sleep until a time point, instead of for a time duration. Using C++'s <chrono> and <thread> libraries, this is incredibly easy:
#include <chrono>
#include <iostream>
#include <thread>
int
main()
{
using namespace std;
using namespace std::chrono;
auto t0 = steady_clock::now() + 10ms;
for (;;)
{
this_thread::sleep_until(t0);
t0 += 10ms;
}
}
One can dress this up with more calls to steady_clock::now() in order to ascertain the time between iterations, and perhaps more importantly, the average iteration time:
#include <chrono>
#include <iostream>
#include <thread>
int
main()
{
using namespace std;
using namespace std::chrono;
using dsec = duration<double>;
auto t0 = steady_clock::now() + 10ms;
auto t1 = steady_clock::now();
auto t2 = t1;
constexpr auto N = 1000;
dsec avg{0};
for (auto i = 0; i < N; ++i)
{
this_thread::sleep_until(t0);
t0 += 10ms;
t2 = steady_clock::now();
dsec delta = t2-t1;
std::cout << delta.count() << "s\n";
avg += delta;
t1 = t2;
}
avg /= N;
cout << "avg = " << avg.count() << "s\n";
}
Above I've added to the loop overhead by doing more things within the loop. However the loop is still going to wake up about every 10ms. Sometimes the OS will wake the thread late, but next time the loop automatically adjusts itself to sleep for a shorter time. Thus the average iteration rate self-corrects to 10ms.
On my machine this just output:
...
0.0102046s
0.0128338s
0.00700504s
0.0116826s
0.00785826s
0.0107023s
0.00912614s
0.0104725s
0.010489s
0.0112545s
0.00906409s
avg = 0.0100014s
There is no way to guarantee 10ms loop time.
All sleeping functions sleeps for at least wanted time.
For a portable solution use std::this_thread::sleep_for
#include <iostream>
#include <chrono>
#include <thread>
int main()
{
for (;;) {
auto start = std::chrono::high_resolution_clock::now();
std::this_thread::sleep_for(std::chrono::milliseconds{10});
auto end = std::chrono::high_resolution_clock::now();
std::chrono::duration<double, std::milli> elapsed = end-start;
std::cout << "Waited " << elapsed.count() << " ms\n";
}
}
Depending on what you are trying to do take a look at Howard Hinnants date library.
From the usleep man page:
The sleep may be lengthened slightly by any system activity or by the time spent processing the call or by the granularity of system timers.
If you need high resolution: with C on Unix (or Linux) check out this answer that explains how to use high resolution timers using clock_gettime.
Edit: As mentioned by Tobias nanosleep may be a better option:
Compared to sleep(3) and usleep(3), nanosleep() has the following
advantages: it provides a higher resolution for specifying the sleep
interval; POSIX.1 explicitly specifies that it does not interact with
signals; and it makes the task of resuming a sleep that has been
interrupted by a signal handler easier.