fix(walltime): use mach_absolute_time for FIFO timestamps on macOS

Mirror the clock used elsewhere in CodSpeed on macOS (mach_absolute_time
with cached mach_timebase_info) so runner and benchmark process
timestamps come from the exact same source. Adds mach2 as a macOS-only
dependency.

Author: not-matthias

Cargo.lock

@@ -78,6 +78,9 @@ crc32fast = "1.5.0"
 [target.'cfg(target_os = "linux")'.dependencies]
 procfs = "0.17.0"
 
+[target.'cfg(target_os = "macos")'.dependencies]
+mach2 = "0.4"
+
 [dev-dependencies]
 temp-env = { version = "0.3.6", features = ["async_closure"] }
 insta = { version = "1.29.0", features = ["json", "redactions"] }

Cargo.toml

@@ -1,7 +1,6 @@
 use crate::prelude::*;
 use anyhow::Context;
 use futures::StreamExt;
-use nix::{sys::time::TimeValLike, time::clock_gettime};
 use runner_shared::artifacts::ExecutionTimestamps;
 use runner_shared::fifo::{Command as FifoCommand, MarkerType};
 use runner_shared::fifo::{RUNNER_ACK_FIFO, RUNNER_CTL_FIFO};
@@ -177,9 +176,37 @@ impl RunnerFifo {
         let mut integration = None;
 
         let current_time = || {
-            clock_gettime(nix::time::ClockId::CLOCK_MONOTONIC)
-                .unwrap()
-                .num_nanoseconds() as u64
+            // Must match the clock used by instrument-hooks (`instrument_hooks_current_timestamp`)
+            // so timestamps from this process and the benchmarked process are comparable.
+            #[cfg(target_os = "macos")]
+            {
+                use mach2::mach_time;
+                use std::sync::OnceLock;
+
+                static NANOS_PER_TICK: OnceLock<mach_time::mach_timebase_info> = OnceLock::new();
+
+                let nanos_per_tick = NANOS_PER_TICK.get_or_init(|| unsafe {
+                    let mut info = mach_time::mach_timebase_info::default();
+                    let errno = mach_time::mach_timebase_info(&mut info as *mut _);
+                    if errno != 0 || info.denom == 0 {
+                        info.numer = 1;
+                        info.denom = 1;
+                    };
+                    info
+                });
+
+                let time = unsafe { mach_time::mach_absolute_time() };
+
+                time * nanos_per_tick.numer as u64 / nanos_per_tick.denom as u64
+            }
+
+            #[cfg(not(target_os = "macos"))]
+            {
+                use nix::{sys::time::TimeValLike, time::clock_gettime};
+
+                let clock = nix::time::ClockId::CLOCK_MONOTONIC;
+                clock_gettime(clock).unwrap().num_nanoseconds() as u64
+            }
         };
 
         let mut benchmark_started = false;