fix: switch to clock_gettime(3) for macOS/iOS for monotonic clock (#97)

This fixes an issue where on M1 (and presumably M2/M3) hardware,
the usage of mach_absolute_time() resulted in undermeasuring the
passage of time when compared to std::time::Instant. Now we read
from the monotonic clock (using clock_gettime, but conceptually
the same as calling mach_continuous_time()) which properly tracks
the passage of time regardless of device sleep, frequency, etc.

Author: tobz

Diff for: .github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
     strategy:
       matrix:
         rust_version: ['1.60.0', 'stable', 'nightly']
-        os: [ubuntu-latest, windows-latest, macOS-latest]
+        os: [ubuntu-20.04, ubuntu-22.04, macOS-11, macOS-12, windows-2019, windows-2022]
     steps:
     - uses: actions/checkout@v3
     - name: Install Rust ${{ matrix.rust_version }}

Diff for: CHANGELOG.md

@@ -8,6 +8,12 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased] - ReleaseDate
 
+### Fixed
+
+- Fixed an issue with the monotonic clock for macOS/iOS where it would undermeasure time compared to
+  what would be measured by `std::time::Instant` due to using a clock source that did not account
+  for device sleep.
+
 ## [0.12.1] - 2023-10-31
 
 ### Fixed

Diff for: Cargo.toml

@@ -47,15 +47,9 @@ raw-cpuid = "11.0"
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 raw-cpuid = "11.0"
 
-[target.'cfg(not(any(target_os = "macos", target_os = "ios", target_os = "windows", target_arch = "wasm32")))'.dependencies]
+[target.'cfg(not(any(target_os = "windows", target_arch = "wasm32")))'.dependencies]
 libc = "0.2"
 
-[target.'cfg(target_os = "macos")'.dependencies]
-mach2 = "0.4"
-
-[target.'cfg(target_os = "ios")'.dependencies]
-mach2 = "0.4"
-
 [target.'cfg(target_os = "windows")'.dependencies]
 winapi = { version = "0.3", features = ["profileapi"] }
 

Diff for: src/clocks/monotonic/macos.rs

@@ -1,8 +1,3 @@
-#[cfg(any(target_os = "macos", target_os = "ios"))]
-mod macos;
-#[cfg(any(target_os = "macos", target_os = "ios"))]
-pub use self::macos::Monotonic;
-
 #[cfg(target_os = "windows")]
 mod windows;
 #[cfg(target_os = "windows")]
@@ -13,17 +8,7 @@ mod wasm;
 #[cfg(target_arch = "wasm32")]
 pub use self::wasm::Monotonic;
 
-#[cfg(not(any(
-    target_os = "macos",
-    target_os = "ios",
-    target_os = "windows",
-    target_arch = "wasm32"
-)))]
+#[cfg(not(any(target_os = "windows", target_arch = "wasm32")))]
 mod unix;
-#[cfg(not(any(
-    target_os = "macos",
-    target_os = "ios",
-    target_os = "windows",
-    target_arch = "wasm32"
-)))]
+#[cfg(not(any(target_os = "windows", target_arch = "wasm32")))]
 pub use self::unix::Monotonic;