fallback.rs - mozsearch

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use std::convert::TryInto;

use std::time::Instant;

use once_cell::sync::Lazy;

static INIT_TIME: Lazy<Instant> = Lazy::new(Instant::now);

pub fn now_including_suspend() -> u64 {

    // For Windows:

    // Instead of relying on figuring out the underlying functions,

    // we can rely on the fact that `Instant::now` maps to [QueryPerformanceCounter] on Windows,

    // so by comparing it to another arbitrary timestamp we will get a duration that will include

    // suspend time.

    // If we use that as a timestamp we can compare later timestamps to it and that will also

    // include suspend time.

//

    // [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter

//

    // For other operating systems:

    // This fallback is not used on Linux, where it maps to `CLOCK_MONOTONIC`, which does NOT

    // include suspend time. But we don't use it there, so no problem.

//

    // This fallback is not used on macOS, where it maps to `mach_absolute_time`, which does NOT

    // include suspend time. But we don't use it there, so no problem.

//

    // For other operating systems we make no guarantees, other than that we won't panic.

    let now = Instant::now();

    now.checked_duration_since(*INIT_TIME)

        .and_then(|diff| diff.as_nanos().try_into().ok())

        .unwrap_or(0)