Adds thread::sleep_until, tracking issue TODO

APC (API change proposal): rust-lang/libs-team#237

Author: dvdsk

library/std/src/thread/mod.rs

@@ -872,6 +872,72 @@ pub fn sleep(dur: Duration) {
     imp::Thread::sleep(dur)
 }
 
+/// Puts the current thread to sleep until the specified deadline has passed.
+///
+/// The thread may still be asleep after the deadline specified due to
+/// scheduling specifics or platform-dependent functionality. It will never
+/// wake before.
+///
+/// This function is blocking, and should not be used in `async` functions.
+///
+/// # Platform-specific behavior
+///
+/// This function uses ['sleep'] internally, see its platform-specific behaviour.
+///
+///
+/// # Examples
+///
+/// A simple game loop that limits the game to 60 frames per second.
+///
+/// '''no_run
+/// # use std::time::{Duration, Instant};
+/// # use std::thread;
+/// #
+/// let max_fps = 60.0;
+/// let frame_time = Duration::from_secs_f32(1.0/max_fps);
+/// let mut next_frame = Instant::now();
+/// loop {
+///     thread::sleep_until(next_frame);
+///     next_frame += frame_time;
+///     update();
+///     render();
+/// }
+/// '''
+///
+/// A slow api we must not call too fast and which takes a few
+/// tries before succeeding. By using `sleep_until` the time the
+/// api call takes does not influence when we retry or when we give up
+///
+/// ```no_run
+/// # use std::time::{Duration, Instant};
+/// # use std::thread;
+/// #
+/// # const MAX_DURATION: Duration = Duration::from_secs(10);
+/// #
+/// let deadline = Instant::now() + MAX_DURATION;
+/// let delay = Duration::from_millis(250);
+/// let mut next_attempt = Instant::now();
+/// loop {
+///     if Instant::now() > deadline {
+///         break Err(()),
+///     }
+///     if let Ready(data) = slow_web_api_call() {
+///         break Ok(data),
+///     }
+///
+///     next_attempt = deadline.min(next_attempt + delay);
+///     thread::sleep_until(next_attempt);
+/// }
+/// ```
+#[unstable(feature = "thread_sleep_until", issue = "todo")]
+pub fn sleep_untill(deadline: Instant) {
+    let now = Instant::now();
+
+    if let Some(delay) = deadline.checked_duration_since(now) {
+        thread::sleep(delay);
+    }
+}
+
 /// Used to ensure that `park` and `park_timeout` do not unwind, as that can
 /// cause undefined behaviour if not handled correctly (see #102398 for context).
 struct PanicGuard;