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use crate::sys::time;
#[inline]
pub(super) fn monotonize(raw: time::Instant) -> time::Instant {
inner::monotonize(raw)
}
#[cfg(all(target_has_atomic = "64", not(target_has_atomic = "128")))]
pub mod inner {
use crate::sync::atomic::AtomicU64;
use crate::sync::atomic::Ordering::*;
use crate::sys::time;
use crate::time::Duration;
const ZERO: time::Instant = time::Instant::zero();
// bits 30 and 31 are never used since the seconds part never exceeds 10^9
const UNINITIALIZED: u64 = 0xff00_0000;
static MONO: AtomicU64 = AtomicU64::new(UNINITIALIZED);
#[inline]
pub(super) fn monotonize(raw: time::Instant) -> time::Instant {
let delta = raw.checked_sub_instant(&ZERO).unwrap();
let secs = delta.as_secs();
// occupies no more than 30 bits (10^9 seconds)
let nanos = delta.subsec_nanos() as u64;
// This wraps around every 136 years (2^32 seconds).
// To detect backsliding we use wrapping arithmetic and declare forward steps smaller
// than 2^31 seconds as expected and everything else as a backslide which will be
// monotonized.
// This could be a problem for programs that call instants at intervals greater
// than 68 years. Interstellar probes may want to ensure that actually_monotonic() is true.
let packed = (secs << 32) | nanos;
let old = MONO.load(Relaxed);
if packed == UNINITIALIZED || packed.wrapping_sub(old) < u64::MAX / 2 {
MONO.store(packed, Relaxed);
raw
} else {
// Backslide occurred. We reconstruct monotonized time by assuming the clock will never
// backslide more than 2`32 seconds which means we can reuse the upper 32bits from
// the seconds.
let secs = (secs & 0xffff_ffff << 32) | old >> 32;
let nanos = old as u32;
ZERO.checked_add_duration(&Duration::new(secs, nanos)).unwrap()
}
}
}
#[cfg(target_has_atomic = "128")]
pub mod inner {
use crate::sync::atomic::AtomicU128;
use crate::sync::atomic::Ordering::*;
use crate::sys::time;
use crate::time::Duration;
const ZERO: time::Instant = time::Instant::zero();
static MONO: AtomicU128 = AtomicU128::new(0);
#[inline]
pub(super) fn monotonize(raw: time::Instant) -> time::Instant {
let delta = raw.checked_sub_instant(&ZERO).unwrap();
// Split into seconds and nanos since Duration doesn't have a
// constructor that takes an u128
let secs = delta.as_secs() as u128;
let nanos = delta.subsec_nanos() as u128;
let timestamp: u128 = secs << 64 | nanos;
let timestamp = MONO.fetch_max(timestamp, Relaxed).max(timestamp);
let secs = (timestamp >> 64) as u64;
let nanos = timestamp as u32;
ZERO.checked_add_duration(&Duration::new(secs, nanos)).unwrap()
}
}
#[cfg(not(any(target_has_atomic = "64", target_has_atomic = "128")))]
pub mod inner {
use crate::cmp;
use crate::sys::time;
use crate::sys_common::mutex::StaticMutex;
#[inline]
pub(super) fn monotonize(os_now: time::Instant) -> time::Instant {
static LOCK: StaticMutex = StaticMutex::new();
static mut LAST_NOW: time::Instant = time::Instant::zero();
unsafe {
let _lock = LOCK.lock();
let now = cmp::max(LAST_NOW, os_now);
LAST_NOW = now;
now
}
}
}
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