boot-time 0.1.3

pub use self::inner::Instant;

const NSEC_PER_SEC: u64 = 1_000_000_000;

#[cfg(any(
    target_os = "macos",
    target_os = "ios",
    target_os = "watchos",
    target_os = "tvos"
))]
mod inner {
    use crate::sys_common::mul_div_u64;
    use std::sync::atomic::{AtomicU64, Ordering};
    use std::time::Duration;

    use super::NSEC_PER_SEC;

    #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
    pub struct Instant {
        t: u64,
    }

    #[repr(C)]
    #[derive(Copy, Clone)]
    #[allow(non_camel_case_types)]
    struct mach_timebase_info {
        numer: u32,
        denom: u32,
    }
    #[allow(non_camel_case_types)]
    type mach_timebase_info_t = *mut mach_timebase_info;
    #[allow(non_camel_case_types)]
    type kern_return_t = libc::c_int;

    impl Instant {
        pub fn now() -> Instant {
            extern "C" {
                fn mach_continuous_time() -> u64;
            }
            Instant {
                t: unsafe { mach_continuous_time() },
            }
        }

        pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
            let diff = self.t.checked_sub(other.t)?;
            let info = info();
            let nanos = mul_div_u64(diff, info.numer as u64, info.denom as u64);
            Some(Duration::new(
                nanos / NSEC_PER_SEC,
                (nanos % NSEC_PER_SEC) as u32,
            ))
        }

        pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
            Some(Instant {
                t: self.t.checked_add(checked_dur2intervals(other)?)?,
            })
        }

        pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
            Some(Instant {
                t: self.t.checked_sub(checked_dur2intervals(other)?)?,
            })
        }
    }

    fn checked_dur2intervals(dur: &Duration) -> Option<u64> {
        let nanos = dur
            .as_secs()
            .checked_mul(NSEC_PER_SEC)?
            .checked_add(dur.subsec_nanos() as u64)?;
        let info = info();
        Some(mul_div_u64(nanos, info.denom as u64, info.numer as u64))
    }

    fn info() -> mach_timebase_info {
        // INFO_BITS conceptually is an `Option<mach_timebase_info>`. We can do
        // this in 64 bits because we know 0 is never a valid value for the
        // `denom` field.
        //
        // Encoding this as a single `AtomicU64` allows us to use `Relaxed`
        // operations, as we are only interested in the effects on a single
        // memory location.
        static INFO_BITS: AtomicU64 = AtomicU64::new(0);

        // If a previous thread has initialized `INFO_BITS`, use it.
        let info_bits = INFO_BITS.load(Ordering::Relaxed);
        if info_bits != 0 {
            return info_from_bits(info_bits);
        }

        // ... otherwise learn for ourselves ...
        extern "C" {
            fn mach_timebase_info(info: mach_timebase_info_t) -> kern_return_t;
        }

        let mut info = info_from_bits(0);
        unsafe {
            mach_timebase_info(&mut info);
        }
        INFO_BITS.store(info_to_bits(info), Ordering::Relaxed);
        info
    }

    #[inline]
    fn info_to_bits(info: mach_timebase_info) -> u64 {
        ((info.denom as u64) << 32) | (info.numer as u64)
    }

    #[inline]
    fn info_from_bits(bits: u64) -> mach_timebase_info {
        mach_timebase_info {
            numer: bits as u32,
            denom: (bits >> 32) as u32,
        }
    }
}

#[cfg(not(any(
    target_os = "macos",
    target_os = "ios",
    target_os = "watchos",
    target_os = "tvos"
)))]
mod inner {
    use super::NSEC_PER_SEC;
    use std::fmt;
    use std::mem::MaybeUninit;
    use std::time::Duration;

    #[doc(hidden)]
    trait IsMinusOne {
        fn is_minus_one(&self) -> bool;
    }

    macro_rules! impl_is_minus_one {
        ($($t:ident)*) => ($(impl IsMinusOne for $t {
            fn is_minus_one(&self) -> bool {
                *self == -1
            }
        })*)
    }

    impl_is_minus_one! { i8 i16 i32 i64 isize }

    fn cvt<T: IsMinusOne>(t: T) -> std::io::Result<T> {
        if t.is_minus_one() {
            Err(std::io::Error::last_os_error())
        } else {
            Ok(t)
        }
    }

    #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    #[repr(transparent)]
    struct Nanoseconds(u32);

    #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub(in crate::sys::unix) struct Timespec {
        tv_sec: i64,
        tv_nsec: Nanoseconds,
    }

    impl Timespec {
        const fn new(tv_sec: i64, tv_nsec: i64) -> Timespec {
            assert!(tv_nsec >= 0 && tv_nsec < NSEC_PER_SEC as i64);
            // SAFETY: The assert above checks tv_nsec is within the valid range
            Timespec {
                tv_sec,
                tv_nsec: Nanoseconds(tv_nsec as u32),
            }
        }

        pub fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
            if self >= other {
                // NOTE(eddyb) two aspects of this `if`-`else` are required for LLVM
                // to optimize it into a branchless form (see also #75545):
                //
                // 1. `self.tv_sec - other.tv_sec` shows up as a common expression
                //    in both branches, i.e. the `else` must have its `- 1`
                //    subtraction after the common one, not interleaved with it
                //    (it used to be `self.tv_sec - 1 - other.tv_sec`)
                //
                // 2. the `Duration::new` call (or any other additional complexity)
                //    is outside of the `if`-`else`, not duplicated in both branches
                //
                // Ideally this code could be rearranged such that it more
                // directly expresses the lower-cost behavior we want from it.
                let (secs, nsec) = if self.tv_nsec.0 >= other.tv_nsec.0 {
                    (
                        (self.tv_sec - other.tv_sec) as u64,
                        self.tv_nsec.0 - other.tv_nsec.0,
                    )
                } else {
                    (
                        (self.tv_sec - other.tv_sec - 1) as u64,
                        self.tv_nsec.0 + (NSEC_PER_SEC as u32) - other.tv_nsec.0,
                    )
                };

                Ok(Duration::new(secs, nsec))
            } else {
                match other.sub_timespec(self) {
                    Ok(d) => Err(d),
                    Err(d) => Ok(d),
                }
            }
        }

        pub fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
            let mut secs = self.tv_sec.checked_add_unsigned(other.as_secs())?;

            // Nano calculations can't overflow because nanos are <1B which fit
            // in a u32.
            let mut nsec = other.subsec_nanos() + self.tv_nsec.0;
            if nsec >= NSEC_PER_SEC as u32 {
                nsec -= NSEC_PER_SEC as u32;
                secs = secs.checked_add(1)?;
            }
            Some(Timespec::new(secs, nsec.into()))
        }

        pub fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
            let mut secs = self.tv_sec.checked_sub_unsigned(other.as_secs())?;

            // Similar to above, nanos can't overflow.
            let mut nsec = self.tv_nsec.0 as i32 - other.subsec_nanos() as i32;
            if nsec < 0 {
                nsec += NSEC_PER_SEC as i32;
                secs = secs.checked_sub(1)?;
            }
            Some(Timespec::new(secs, nsec.into()))
        }

        #[allow(dead_code)]
        pub fn to_timespec(&self) -> Option<libc::timespec> {
            Some(libc::timespec {
                tv_sec: self.tv_sec.try_into().ok()?,
                tv_nsec: self.tv_nsec.0.try_into().ok()?,
            })
        }

        // On QNX Neutrino, the maximum timespec for e.g. pthread_cond_timedwait
        // is 2^64 nanoseconds
        #[cfg(target_os = "nto")]
        pub(super) fn to_timespec_capped(&self) -> Option<libc::timespec> {
            // Check if timeout in nanoseconds would fit into an u64
            if (self.tv_nsec.0 as u64)
                .checked_add((self.tv_sec as u64).checked_mul(NSEC_PER_SEC)?)
                .is_none()
            {
                return None;
            }
            self.to_timespec()
        }

        #[cfg(all(
            target_os = "linux",
            target_env = "gnu",
            target_pointer_width = "32",
            not(target_arch = "riscv32")
        ))]
        pub fn to_timespec64(&self) -> __timespec64 {
            __timespec64::new(self.tv_sec, self.tv_nsec.0 as _)
        }
    }

    impl From<libc::timespec> for Timespec {
        fn from(t: libc::timespec) -> Timespec {
            Timespec::new(t.tv_sec as i64, t.tv_nsec as i64)
        }
    }

    #[cfg(all(
        target_os = "linux",
        target_env = "gnu",
        target_pointer_width = "32",
        not(target_arch = "riscv32")
    ))]
    #[repr(C)]
    pub(in crate::sys::unix) struct __timespec64 {
        pub(in crate::sys::unix) tv_sec: i64,
        #[cfg(target_endian = "big")]
        _padding: i32,
        pub(in crate::sys::unix) tv_nsec: i32,
        #[cfg(target_endian = "little")]
        _padding: i32,
    }

    #[cfg(all(
        target_os = "linux",
        target_env = "gnu",
        target_pointer_width = "32",
        not(target_arch = "riscv32")
    ))]
    impl __timespec64 {
        pub(in crate::sys::unix) fn new(tv_sec: i64, tv_nsec: i32) -> Self {
            Self {
                tv_sec,
                tv_nsec,
                _padding: 0,
            }
        }
    }

    #[cfg(all(
        target_os = "linux",
        target_env = "gnu",
        target_pointer_width = "32",
        not(target_arch = "riscv32")
    ))]
    impl From<__timespec64> for Timespec {
        fn from(t: __timespec64) -> Timespec {
            Timespec::new(t.tv_sec, t.tv_nsec.into())
        }
    }

    #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub struct Instant {
        t: Timespec,
    }

    impl Instant {
        pub fn now() -> Instant {
            cfg_if::cfg_if! {
                if #[cfg(any(
                    target_os = "linux",
                    target_os = "l4re",
                    target_os = "android",
                    target_os = "openbsd",
                ))] {
                    #[allow(non_upper_case_globals)]
                    const clock_id: libc::clockid_t = libc::CLOCK_BOOTTIME;
                } else {
                    #[allow(non_upper_case_globals)]
                    const clock_id: libc::clockid_t = libc::CLOCK_MONOTONIC;
                }
            }
            Instant {
                t: Timespec::now(clock_id),
            }
        }

        pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
            self.t.sub_timespec(&other.t).ok()
        }

        pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
            Some(Instant {
                t: self.t.checked_add_duration(other)?,
            })
        }

        pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
            Some(Instant {
                t: self.t.checked_sub_duration(other)?,
            })
        }
    }

    impl fmt::Debug for Instant {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("Instant")
                .field("tv_sec", &self.t.tv_sec)
                .field("tv_nsec", &self.t.tv_nsec.0)
                .finish()
        }
    }

    impl Timespec {
        pub fn now(clock: libc::clockid_t) -> Timespec {
            let mut t = MaybeUninit::uninit();
            cfg_if::cfg_if! {
                // Try to use 64-bit time in preparation for Y2038.
                if #[cfg(all(
                    target_os = "linux",
                    target_env = "gnu",
                    target_pointer_width = "32",
                    not(target_arch = "riscv32")
                ))]
                {
                    // SAFETY: These declarations must match the definitions in the system's C library (glibc).
                    // 1. `timespec64` is defined with a 64-bit `tv_sec` to match the `__clock_gettime64`
                    //    ABI on 32-bit systems (glibc 2.34+).
                    // 2. The function signature and symbol name `__clock_gettime64` are verified to exist
                    //    in the target environment's libc.
                    // 3. The `clock_id` and pointer usage follow the documented POSIX/glibc requirements.
                    unsafe extern "C" {
                        /// Links to the 64-bit time function in glibc.
                        ///
                        /// __clock_gettime64 was added to 32-bit arches in glibc 2.34,
                        /// and it handles both vDSO calls and ENOSYS fallbacks itself.
                        ///
                        /// # Safety
                        /// The caller must ensure `tp` points to a valid, aligned `timespec64` struct.
                        fn __clock_gettime64(clock_id: i32, tp: *mut __timespec64) -> i32;
                    }
                    cvt(unsafe { __clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
                } else {
                    cvt(unsafe { libc::clock_gettime(clock, t.as_mut_ptr()) }).unwrap();
                }
            }
            Timespec::from(unsafe { t.assume_init() })
        }
    }
}