xu-cheng / howlong Goto Github PK

Thank you for this library!

A thing that confuses me is the difference between

let wall_clock = howlong::HighResolutionClock::now();
let elapsed_wall_time = howlong::HighResolutionClock::now() - wall_clock;

println!(elapsed_wall_time);

and

let cpu_clock = howlong::ProcessCPUClock::now();
let elapsed_cpu_time = howlong::ProcessCPUClock::now() - cpu_clock;

println!(elapsed_cpu_time.real);

Colloquially, "real" time is "wall clock" time, which seems to correspond to SystemClock (which is aliased by HighResolutionClock) per this crate's docs and in the parlance of the Boost library's docs with their system_clock.

But "CPU time" is colloquially "process user (out-of-kernel) time + process system (in-kernel) time", which would seem to correspond to:

elapsed_cpu_time.user.as_secs() + elapsed_cpu_time.system.as_secs()

But then what's elapsed_cpu_time.real? Boost docs corroborate this terminology ("timing information is broken down into real (wall clock) time, CPU time spent by the user, and CPU time spent by the operating system servicing user requests.") but don't seem to explain what the difference is between their process_real_cpu_clock and system_clock.

Some clarification in the docs would be great!

Steps to reproduce:

1. Create a new project with the following Cargo.toml:

   [package]
   name = "example"
   version = "0.1.0"
   edition = "2018"
   resolver = "2"
   
   [dependencies]
   howlong = "0.1"
   

2. Run cargo check

I get the following error:

error[E0432]: unresolved imports `winapi::um::errhandlingapi`, `winapi::um::processthreadsapi`
 --> C:\Users\username\.cargo\registry\src\github.com-1ecc6299db9ec823\howlong-0.1.6\src\clock\win.rs:6:5
  |
6 |     errhandlingapi::GetLastError,
  |     ^^^^^^^^^^^^^^ could not find `errhandlingapi` in `um`
7 |     processthreadsapi::{GetCurrentProcess, GetCurrentThread, GetProcessTimes, GetThreadTimes},
  |     ^^^^^^^^^^^^^^^^^ could not find `processthreadsapi` in `um`