Specialize sleep_until implementation

library/std/src/sys/pal/hermit/thread.rs

@@ -82,6 +82,14 @@ impl Thread {
         }
     }
 
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         unsafe {
             let _ = hermit_abi::join(self.tid);

library/std/src/sys/pal/itron/thread.rs

@@ -205,6 +205,14 @@ impl Thread {
         }
     }
 
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         // Safety: `ThreadInner` is alive at this point
         let inner = unsafe { self.p_inner.as_ref() };

library/std/src/sys/pal/sgx/thread.rs

@@ -130,6 +130,14 @@ impl Thread {
         usercalls::wait_timeout(0, dur, || true);
     }
 
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         self.0.wait();
     }

library/std/src/sys/pal/unix/thread.rs

@@ -264,6 +264,93 @@ impl Thread {
         }
     }
 
+    #[cfg(not(any(
+        target_os = "freebsd",
+        target_os = "netbsd",
+        target_os = "linux",
+        target_os = "android",
+        target_os = "solaris",
+        target_os = "illumos",
+        target_os = "dragonfly",
+        target_os = "hurd",
+        target_os = "fuchsia",
+        target_os = "vxworks",
+        target_vendor = "apple"
+    )))]
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            sleep(delay);
+        }
+    }
+
+    // Note depends on clock_nanosleep (not supported on os's by apple)
+    #[cfg(any(
+        target_os = "freebsd",
+        target_os = "netbsd",
+        target_os = "linux",
+        target_os = "android",
+        target_os = "solaris",
+        target_os = "illumos",
+        target_os = "dragonfly",
+        target_os = "hurd",
+        target_os = "fuchsia",
+        target_os = "vxworks",
+    ))]
+    pub fn sleep_until(deadline: crate::time::Instant) {
+        let mut ts = deadline
+            .into_inner()
+            .into_timespec()
+            .to_timespec()
+            .expect("Timespec is narrower then libc::timespec thus conversion can't fail");
+        let ts_ptr = &mut ts as *mut _;
+
+        // If we're awoken with a signal and the return value is -1
+        // clock_nanosleep needs to be called again.
+        unsafe {
+            while libc::clock_nanosleep(libc::CLOCK_MONOTONIC, libc::TIMER_ABSTIME, ts_ptr, ts_ptr)
+                == -1
+            {
+                assert_eq!(
+                    os::errno(),
+                    libc::EINTR,
+                    "clock nanosleep should only return an error if interrupted"
+                );
+            }
+        }
+    }
+
+    #[cfg(target_vendor = "apple")]
+    pub fn sleep_until(deadline: crate::time::Instant) {
+        use core::mem::MaybeUninit;
+
+        use super::time::Timespec;
+
+        let Timespec { tv_sec, tv_nsec } = deadline.into_inner().into_timespec();
+        let nanos = (tv_sec as u64).saturating_mul(1_000_000_000).saturating_add(tv_nsec.0 as u64);
+
+        let mut info = MaybeUninit::uninit();
+        unsafe {
+            let ret = mach_timebase_info(info.as_mut_ptr());
+            assert_eq!(ret, KERN_SUCCESS);
+
+            let info = info.assume_init();
+            let ticks = nanos * (info.denom as u64) / (info.numer as u64);
+
+            loop {
+                // There are no docs on the mach_wait_until some details can be
+                // learned from the `Apple OSS Distributions` xnu source code.
+                // Specifically: xnu/osfmk/clock.h commit 94d3b45 on Github
+                let ret = mach_wait_until(ticks);
+                if ret != KERN_ABORTED {
+                    break;
+                }
+            }
+            assert_eq!(ret, KERN_SUCCESS);
+        }
+    }
+
     pub fn join(self) {
         let id = self.into_id();
         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
@@ -279,6 +366,27 @@ impl Thread {
     }
 }
 
+// these come from the `Apple OSS Distributions` xnu source code.
+// Specifically: xnu/osfmk/mach/kern_return.h commit 94d3b45 on Github
+#[cfg(target_vendor = "apple")]
+const KERN_SUCCESS: libc::c_int = 0;
+#[cfg(target_vendor = "apple")]
+const KERN_ABORTED: libc::c_int = 14;
+
+#[cfg(target_vendor = "apple")]
+#[repr(C)]
+struct mach_timebase_info_type {
+    numer: u32,
+    denom: u32,
+}
+
+#[cfg(target_vendor = "apple")]
+extern "C" {
+    fn mach_wait_until(deadline: u64) -> libc::c_int;
+    fn mach_timebase_info(info: *mut mach_timebase_info_type) -> libc::c_int;
+
+}
+
 impl Drop for Thread {
     fn drop(&mut self) {
         let ret = unsafe { libc::pthread_detach(self.id) };

library/std/src/sys/pal/unix/time.rs

@@ -19,7 +19,7 @@ pub(in crate::sys) const TIMESPEC_MAX_CAPPED: libc::timespec = libc::timespec {
 #[repr(transparent)]
 #[rustc_layout_scalar_valid_range_start(0)]
 #[rustc_layout_scalar_valid_range_end(999_999_999)]
-struct Nanoseconds(u32);
+pub(crate) struct Nanoseconds(pub(crate) u32);
 
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct SystemTime {
@@ -28,8 +28,8 @@ pub struct SystemTime {
 
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub(crate) struct Timespec {
-    tv_sec: i64,
-    tv_nsec: Nanoseconds,
+    pub(crate) tv_sec: i64,
+    pub(crate) tv_nsec: Nanoseconds,
 }
 
 impl SystemTime {
@@ -287,6 +287,10 @@ impl Instant {
     pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
         Some(Instant { t: self.t.checked_sub_duration(other)? })
     }
+
+    pub(crate) fn into_timespec(self) -> Timespec {
+        self.t
+    }
 }
 
 impl fmt::Debug for Instant {

library/std/src/sys/pal/wasi/thread.rs

@@ -1,7 +1,7 @@
 use crate::ffi::CStr;
 use crate::num::NonZero;
 use crate::sys::unsupported;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{io, mem};
 
 cfg_if::cfg_if! {
@@ -137,35 +137,18 @@ impl Thread {
         let nanos = dur.as_nanos();
         assert!(nanos <= u64::MAX as u128);
 
-        const USERDATA: wasi::Userdata = 0x0123_45678;
-
-        let clock = wasi::SubscriptionClock {
-            id: wasi::CLOCKID_MONOTONIC,
-            timeout: nanos as u64,
-            precision: 0,
-            flags: 0,
-        };
-
-        let in_ = wasi::Subscription {
-            userdata: USERDATA,
-            u: wasi::SubscriptionU { tag: 0, u: wasi::SubscriptionUU { clock } },
-        };
-        unsafe {
-            let mut event: wasi::Event = mem::zeroed();
-            let res = wasi::poll_oneoff(&in_, &mut event, 1);
-            match (res, event) {
-                (
-                    Ok(1),
-                    wasi::Event {
-                        userdata: USERDATA,
-                        error: wasi::ERRNO_SUCCESS,
-                        type_: wasi::EVENTTYPE_CLOCK,
-                        ..
-                    },
-                ) => {}
-                _ => panic!("thread::sleep(): unexpected result of poll_oneoff"),
-            }
-        }
+        sleep_with(nanos as u64, wasi::CLOCKID_MONOTONIC, 0);
+    }
+
+    pub fn sleep_until(deadline: Instant) {
+        let nanos = deadline.into_inner().into_inner().as_nanos();
+        assert!(nanos <= u64::MAX as u128);
+
+        sleep_with(
+            nanos as u64,
+            wasi::CLOCKID_MONOTONIC,
+            wasi::SUBCLOCKFLAGS_SUBSCRIPTION_CLOCK_ABSTIME,
+        );
     }
 
     pub fn join(self) {
@@ -183,6 +166,32 @@ impl Thread {
     }
 }
 
+fn sleep_with(nanos: u64, clock_id: wasi::Clockid, flags: u16) {
+    let clock = wasi::SubscriptionClock { id: clock_id, timeout: nanos, precision: 0, flags };
+
+    const USERDATA: wasi::Userdata = 0x0123_45678;
+    let in_ = wasi::Subscription {
+        userdata: USERDATA,
+        u: wasi::SubscriptionU { tag: 0, u: wasi::SubscriptionUU { clock } },
+    };
+    unsafe {
+        let mut event: wasi::Event = mem::zeroed();
+        let res = wasi::poll_oneoff(&in_, &mut event, 1);
+        match (res, event) {
+            (
+                Ok(1),
+                wasi::Event {
+                    userdata: USERDATA,
+                    error: wasi::ERRNO_SUCCESS,
+                    type_: wasi::EVENTTYPE_CLOCK,
+                    ..
+                },
+            ) => {}
+            _ => panic!("thread::sleep(): unexpected result of poll_oneoff"),
+        }
+    }
+}
+
 pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     unsupported()
 }

library/std/src/sys/pal/wasi/time.rs

@@ -36,6 +36,10 @@ impl Instant {
     pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
         Some(Instant(self.0.checked_sub(*other)?))
     }
+
+    pub(crate) fn into_inner(self) -> Duration {
+        self.0
+    }
 }
 
 impl SystemTime {

library/std/src/sys/pal/windows/thread.rs

@@ -8,7 +8,7 @@ use crate::os::windows::io::{AsRawHandle, HandleOrNull};
 use crate::sys::handle::Handle;
 use crate::sys::{c, stack_overflow};
 use crate::sys_common::FromInner;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{io, ptr};
 
 pub const DEFAULT_MIN_STACK_SIZE: usize = 2 * 1024 * 1024;
@@ -105,6 +105,14 @@ impl Thread {
         }
     }
 
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            Self::sleep(delay);
+        }
+    }
+
     pub fn handle(&self) -> &Handle {
         &self.handle
     }

library/std/src/sys/pal/xous/thread.rs

@@ -128,6 +128,14 @@ impl Thread {
         }
     }
 
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         join_thread(self.tid).unwrap();
     }

library/std/src/thread/mod.rs

@@ -926,8 +926,36 @@ pub fn sleep(dur: Duration) {
 ///
 /// # Platform-specific behavior
 ///
-/// This function uses [`sleep`] internally, see its platform-specific behaviour.
+/// In most cases this function will an call OS specific function. Where that
+/// is not supported [`sleep`] is used. Those platforms are referred to as other
+/// in the table below.
 ///
+/// # Underlying System calls
+///
+/// The following system calls are [currently] being used:
+///
+///
+/// |  Platform |               System call                                            |
+/// |-----------|----------------------------------------------------------------------|
+/// | Linux     | [clock_nanosleep] (Monotonic clock)                                  |
+/// | BSD except OpenBSD | [clock_nanosleep] (Monotonic Clock)]                        |
+/// | Android   | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Solaris   | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Illumos   | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Dragonfly | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Hurd      | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Fuchsia   | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Vxworks   | [clock_nanosleep] (Monotonic Clock)]                                 |
+/// | Darwin    | [mach_wait_until]                                                    |
+/// | WASI      | [subscription_clock]                                                 |
+/// | Other     | `sleep_until` uses [`sleep`] and does not issue a syscall itself     |
+///
+/// [currently]: crate::io#platform-specific-behavior
+/// [clock_nanosleep]: https://linux.die.net/man/3/clock_nanosleep
+/// [subscription_clock]: https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md#-subscription_clock-record
+/// [mach_wait_until]: https://developer.apple.com/library/archive/technotes/tn2169/_index.html
+///
+/// **Disclaimer:** These system calls might change over time.
 ///
 /// # Examples
 ///
@@ -989,11 +1017,7 @@ pub fn sleep(dur: Duration) {
 /// ```
 #[unstable(feature = "thread_sleep_until", issue = "113752")]
 pub fn sleep_until(deadline: Instant) {
-    let now = Instant::now();
-
-    if let Some(delay) = deadline.checked_duration_since(now) {
-        sleep(delay);
-    }
+    imp::Thread::sleep_until(deadline)
 }
 
 /// Used to ensure that `park` and `park_timeout` do not unwind, as that can