sleep_until: use clock_nanosleep where possible

Using clock nanosleep leads to more accurate sleep times on platforms
where it is supported.

To enable using clock_nanosleep this makes `sleep_until` platform
specific. That unfortunatly requires identical placeholder
implementations for the other platforms (windows/mac/wasm etc).

we will land platform specific implementations for those later. See the
`sleep_until` tracking issue.

This requires an accessors for the Instant type. As that accessor is only
used on the platforms that have clock_nanosleep it is marked as allow_unused.

32bit time_t targets do not use clock_nanosleep atm, they instead rely
on the same placeholder as the other platforms. We could make them
use clock_nanosleep too in the future using `__clock_nanosleep_time64`.

__clock_nanosleep_time64 is documented at:
https://www.gnu.org/software/libc/manual/html_node/64_002dbit-time-symbol-handling.html

Author: dvdsk

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

@@ -4,7 +4,7 @@ use super::hermit_abi;
 use crate::ffi::CStr;
 use crate::mem::ManuallyDrop;
 use crate::num::NonZero;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{io, ptr};
 
 pub type Tid = hermit_abi::Tid;
@@ -86,6 +86,14 @@ 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 join(self) {
         unsafe {
             let _ = hermit_abi::join(self.tid);

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

@@ -10,7 +10,7 @@ use crate::mem::ManuallyDrop;
 use crate::num::NonZero;
 use crate::ptr::NonNull;
 use crate::sync::atomic::{Atomic, AtomicUsize, Ordering};
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{hint, io};
 
 pub struct Thread {
@@ -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) {
+            Self::sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         // Safety: `ThreadInner` is alive at this point
         let inner = unsafe { self.p_inner.as_ref() };

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

@@ -5,7 +5,7 @@ use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
 use crate::num::NonZero;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 
 pub struct Thread(task_queue::JoinHandle);
 
@@ -132,6 +132,14 @@ 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) {
+            Self::sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         self.0.wait();
     }

std/src/sys/pal/teeos/thread.rs

@@ -2,7 +2,7 @@ use crate::ffi::CStr;
 use crate::mem::{self, ManuallyDrop};
 use crate::num::NonZero;
 use crate::sys::os;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{cmp, io, ptr};
 
 pub const DEFAULT_MIN_STACK_SIZE: usize = 8 * 1024;
@@ -109,6 +109,14 @@ impl Thread {
         }
     }
 
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            Self::sleep(delay);
+        }
+    }
+
     /// must join, because no pthread_detach supported
     pub fn join(self) {
         let id = self.into_id();

std/src/sys/pal/uefi/thread.rs

@@ -3,7 +3,7 @@ use crate::ffi::CStr;
 use crate::io;
 use crate::num::NonZero;
 use crate::ptr::NonNull;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 
 pub struct Thread(!);
 
@@ -39,6 +39,14 @@ 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 join(self) {
         self.0
     }

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

@@ -6,7 +6,7 @@ use crate::sys::weak::dlsym;
 #[cfg(any(target_os = "solaris", target_os = "illumos", target_os = "nto",))]
 use crate::sys::weak::weak;
 use crate::sys::{os, stack_overflow};
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{cmp, io, ptr};
 #[cfg(not(any(
     target_os = "l4re",
@@ -296,6 +296,75 @@ impl Thread {
         }
     }
 
+    // Any unix that has clock_nanosleep
+    #[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: Instant) {
+        let Some(ts) = deadline.into_inner().into_timespec().to_timespec() else {
+            // The deadline is further in the future then can be passed to
+            // clock_nanosleep. We have to use Self::sleep instead. This might
+            // happen on 32 bit platforms, especially closer to 2038.
+            let now = Instant::now();
+            if let Some(delay) = deadline.checked_duration_since(now) {
+                Self::sleep(delay);
+            }
+            return;
+        };
+
+        unsafe {
+            // When we get interrupted (res = EINTR) call clock_nanosleep again
+            loop {
+                let res = libc::clock_nanosleep(
+                    super::time::Instant::CLOCK_ID,
+                    libc::TIMER_ABSTIME,
+                    &ts,
+                    core::ptr::null_mut(), // not required with TIMER_ABSTIME
+                );
+
+                if res == 0 {
+                    break;
+                } else {
+                    assert_eq!(
+                        res,
+                        libc::EINTR,
+                        "timespec is in range,
+                         clockid is valid and kernel should support it"
+                    );
+                }
+            }
+        }
+    }
+
+    // Any unix that does not have clock_nanosleep
+    #[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",
+    )))]
+    pub fn sleep_until(deadline: Instant) {
+        let now = Instant::now();
+        if let Some(delay) = deadline.checked_duration_since(now) {
+            Self::sleep(delay);
+        }
+    }
+
     pub fn join(self) {
         let id = self.into_id();
         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };

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

@@ -261,6 +261,10 @@ pub struct Instant {
 }
 
 impl Instant {
+    #[cfg(target_vendor = "apple")]
+    pub(crate) const CLOCK_ID: libc::clockid_t = libc::CLOCK_UPTIME_RAW;
+    #[cfg(not(target_vendor = "apple"))]
+    pub(crate) const CLOCK_ID: libc::clockid_t = libc::CLOCK_MONOTONIC;
     pub fn now() -> Instant {
         // https://www.manpagez.com/man/3/clock_gettime/
         //
@@ -273,11 +277,7 @@ impl Instant {
         //
         // Instant on macos was historically implemented using mach_absolute_time;
         // we preserve this value domain out of an abundance of caution.
-        #[cfg(target_vendor = "apple")]
-        const clock_id: libc::clockid_t = libc::CLOCK_UPTIME_RAW;
-        #[cfg(not(target_vendor = "apple"))]
-        const clock_id: libc::clockid_t = libc::CLOCK_MONOTONIC;
-        Instant { t: Timespec::now(clock_id) }
+        Instant { t: Timespec::now(Self::CLOCK_ID) }
     }
 
     pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
@@ -291,6 +291,14 @@ impl Instant {
     pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
         Some(Instant { t: self.t.checked_sub_duration(other)? })
     }
+
+    #[cfg_attr(
+        not(target_os = "linux"),
+        allow(unused, reason = "needed by the `sleep_until` on some unix platforms")
+    )]
+    pub(crate) fn into_timespec(self) -> Timespec {
+        self.t
+    }
 }
 
 impl fmt::Debug for Instant {

std/src/sys/pal/unsupported/thread.rs

@@ -2,7 +2,7 @@ use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
 use crate::num::NonZero;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 
 pub struct Thread(!);
 
@@ -26,6 +26,10 @@ impl Thread {
         panic!("can't sleep");
     }
 
+    pub fn sleep_until(_deadline: Instant) {
+        panic!("can't sleep");
+    }
+
     pub fn join(self) {
         self.0
     }

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

@@ -2,7 +2,7 @@
 
 use crate::ffi::CStr;
 use crate::num::NonZero;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 use crate::{io, mem};
 
 cfg_if::cfg_if! {
@@ -171,6 +171,14 @@ 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 join(self) {
         cfg_if::cfg_if! {
             if #[cfg(target_feature = "atomics")] {

std/src/sys/pal/wasm/atomics/thread.rs

@@ -2,7 +2,7 @@ use crate::ffi::CStr;
 use crate::io;
 use crate::num::NonZero;
 use crate::sys::unsupported;
-use crate::time::Duration;
+use crate::time::{Duration, Instant};
 
 pub struct Thread(!);
 
@@ -41,6 +41,14 @@ 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 join(self) {}
 }