使用C ++ 11的可移植计时代码的正确方法 [英] Correct way of portably timing code using C++11
问题描述
我正在为要求低延迟的程序的一部分编写一些时序代码.
I'm in the midst of writing some timing code for a part of a program that has a low latency requirement.
看看std :: chrono库中的可用内容,我发现编写可移植的计时代码有点困难.
Looking at whats available in the std::chrono library, I'm finding it a bit difficult to write timing code that is portable.
- std :: chrono :: high_resolution_clock
- std :: chrono :: steady_clock
- std :: chrono :: system_clock
system_clock没用,因为它不稳定,剩下的两个时钟有问题.
The system_clock is useless as it's not steady, the remaining two clocks are problematic.
high_resolution_clock不一定在所有平台上都稳定.
The high_resolution_clock isn't necessarily stable on all platforms.
steady_clock不一定支持精细的分辨率时间段(例如:纳秒)
The steady_clock does not necessarily support fine-grain resolution time periods (eg: nano seconds)
出于我的目的,保持时钟稳定是最重要的要求,我可以通过微秒级的粒度来解决问题.
For my purposes having a steady clock is the most important requirement and I can sort of get by with microsecond granularity.
我的问题是,是否想计时可以在不同硬件架构和操作系统上运行的代码-最佳选择是什么?
My question is if one wanted to time code that could be running on different h/w architectures and OSes - what would be the best option?
推荐答案
使用steady_clock
.在所有实现中,其精度均为纳秒.您可以通过打印steady_clock::period::num
和steady_clock::period::den
来针对自己的平台进行检查.
Use steady_clock
. On all implementations its precision is nanoseconds. You can check this yourself for your platform by printing out steady_clock::period::num
and steady_clock::period::den
.
现在,这并不意味着它将实际测量纳秒精度.但是平台会尽力而为.对我来说,连续两次调用steady_clock
(启用了优化)将报告时间间隔为100ns.
Now that doesn't mean that it will actually measure nanosecond precision. But platforms do their best. For me, two consecutive calls to steady_clock
(with optimizations enabled) will report times on the order of 100ns apart.
#include "chrono_io.h"
#include <chrono>
#include <iostream>
int
main()
{
using namespace std::chrono;
using namespace date;
auto t0 = steady_clock::now();
auto t1 = steady_clock::now();
auto t2 = steady_clock::now();
auto t3 = steady_clock::now();
std::cout << t1-t0 << '\n';
std::cout << t2-t1 << '\n';
std::cout << t3-t2 << '\n';
}
上面的示例使用了免费,开放源代码,仅标头的库仅用于格式化持续时间.您可以自己格式化(我很懒).对我来说,这只是输出:
The above example uses this free, open-source, header-only library only for convenience of formatting the duration. You can format things yourself (I'm lazy). For me this just output:
287ns
116ns
75ns
YMMV.
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