Aggregate wall time of code blocks in C++ - c++

Question

I have a large codebase and I want to manually add some timers to profile some sections of the code.
Some of those sections are within a loop, so I would like to aggregate all the wall time spent there for each iteration.
What I'd like to do in a Pythonic pseudo-code:
time_step_1 = 0
time_step_2 = 0
for pair in pairs:
start_step_1 = time.now()
run_step_1(pair)
time_step_1 += start_step_1 - time.now()
start_step_2 = time.now()
run_step_2(pair)
time_step_2 += start_step_2 - time.now()
print("Time spent in step 1", time_step_1)
print("Time spent in step 2", time_step_2)
Is there a library in C++ to do this?
Otherwise would you recommend using boost::timer, create a map of timers and then resume and stop at each iteration?

Answer 1

Not very advanced, but for basic time measurement, you can use std::chrono library, specifically the std::chrono::high_resolution_clock - the clock
with smallest tick period (= highest accuracy) provided by the implementation.
For some more trivial time measurement, I have used RAII classes similar to this:
#include <chrono>
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <string>
class TimeMeasureGuard {
public:
using clock_type = std::chrono::high_resolution_clock;
private:
const std::string m_testName;
std::ostream& m_os;
clock_type::time_point started_at;
clock_type::time_point ended_at;
public:
TimeMeasureGuard(const std::string& testName, std::ostream& os = std::cerr)
: m_testName(testName), m_os(os)
{
started_at = clock_type::now();
}
~TimeMeasureGuard()
{
ended_at = clock_type::now();
// Get duration
const auto duration = ended_at - started_at;
// Get duration in nanoseconds
const auto durationNs = std::chrono::nanoseconds(duration).count();
// ...or in microseconds:
const auto durationUs
= std::chrono::duration_cast<std::chrono::microseconds>(duration).count();
// Report total run time into 'm_os' stream
m_os << "[Test " << std::quoted(m_testName) << "]: Total run time: "
<< durationNs << " ns, " << "or: " << durationUs << " us" << std::endl;
}
};
Of course this is a very simple class, which would deserve several improvements before being used for a real measurement.
You can use this class like:
std::uint64_t computeSquares()
{
std::uint64_t interestingNumbers = 0;
{
auto time_measurement = TimeMeasureGuard("Test1");
for (std::uint64_t x = 0; x < 1'000; ++x) {
for (std::uint64_t y = 0; y < 1'000; ++y) {
if ((x * y) % 42 == 0)
++interestingNumbers;
}
}
}
return interestingNumbers;
}
int main()
{
std::cout << "Computing all x * y, where 'x' and 'y' are from 1 to 1'000..."
<< std::endl;
const auto res = computeSquares();
std::cerr << "Interesting numbers found: " << res << std::endl;
return 0;
}
And the output is:
Computing all x * y, where 'x' and 'y' are from 1 to 1'000...
[Test "Test1"]: Total run time: 6311371 ns, or: 6311 us
Interesting numbers found: 111170
For simple time measurement cases, this might be easier than using
a whole timer library, and it's just a few lines of code, you don't
need to include lots of headers.