1 files changed, 31 insertions, 0 deletions
diff --git a/third_party/rust/zeitstempel/src/fallback.rs b/third_party/rust/zeitstempel/src/fallback.rs
new file mode 100644
index 0000000000..157f4c1a77
--- /dev/null
+++ b/third_party/rust/zeitstempel/src/fallback.rs
@@ -0,0 +1,31 @@
+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)
+}