1 files changed, 38 insertions, 0 deletions
diff --git a/library/std/src/sys/windows/time.rs b/library/std/src/sys/windows/time.rs
index b8209a854..bece48e79 100644
--- a/library/std/src/sys/windows/time.rs
+++ b/library/std/src/sys/windows/time.rs
@@ -1,11 +1,13 @@
 use crate::cmp::Ordering;
 use crate::fmt;
 use crate::mem;
+use crate::ptr::{null, null_mut};
 use crate::sys::c;
 use crate::sys_common::IntoInner;
 use crate::time::Duration;
 
 use core::hash::{Hash, Hasher};
+use core::ops::Neg;
 
 const NANOS_PER_SEC: u64 = 1_000_000_000;
 const INTERVALS_PER_SEC: u64 = NANOS_PER_SEC / 100;
@@ -222,3 +224,39 @@ mod perf_counter {
         qpc_value
     }
 }
+
+/// A timer you can wait on.
+pub(super) struct WaitableTimer {
+    handle: c::HANDLE,
+}
+impl WaitableTimer {
+    /// Create a high-resolution timer. Will fail before Windows 10, version 1803.
+    pub fn high_resolution() -> Result<Self, ()> {
+        let handle = unsafe {
+            c::CreateWaitableTimerExW(
+                null(),
+                null(),
+                c::CREATE_WAITABLE_TIMER_HIGH_RESOLUTION,
+                c::TIMER_ALL_ACCESS,
+            )
+        };
+        if handle != null_mut() { Ok(Self { handle }) } else { Err(()) }
+    }
+    pub fn set(&self, duration: Duration) -> Result<(), ()> {
+        // Convert the Duration to a format similar to FILETIME.
+        // Negative values are relative times whereas positive values are absolute.
+        // Therefore we negate the relative duration.
+        let time = checked_dur2intervals(&duration).ok_or(())?.neg();
+        let result = unsafe { c::SetWaitableTimer(self.handle, &time, 0, None, null(), c::FALSE) };
+        if result != 0 { Ok(()) } else { Err(()) }
+    }
+    pub fn wait(&self) -> Result<(), ()> {
+        let result = unsafe { c::WaitForSingleObject(self.handle, c::INFINITE) };
+        if result != c::WAIT_FAILED { Ok(()) } else { Err(()) }
+    }
+}
+impl Drop for WaitableTimer {
+    fn drop(&mut self) {
+        unsafe { c::CloseHandle(self.handle) };
+    }
+}