diff options
| -rw-r--r-- | library/std/src/lib.rs | 1 | ||||
| -rw-r--r-- | library/std/src/time/monotonic.rs | 57 |
2 files changed, 30 insertions, 28 deletions
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs index 559d2672a0d..f69baba9e73 100644 --- a/library/std/src/lib.rs +++ b/library/std/src/lib.rs @@ -234,6 +234,7 @@ #![feature(atomic_mut_ptr)] #![feature(auto_traits)] #![feature(bench_black_box)] +#![feature(bool_to_option)] #![feature(box_syntax)] #![feature(c_unwind)] #![feature(c_variadic)] diff --git a/library/std/src/time/monotonic.rs b/library/std/src/time/monotonic.rs index fa96b7abff6..198ae739b55 100644 --- a/library/std/src/time/monotonic.rs +++ b/library/std/src/time/monotonic.rs @@ -37,35 +37,36 @@ pub mod inner { // 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 old == UNINITIALIZED || packed.wrapping_sub(old) < u64::MAX / 2 { - mono.store(packed, Relaxed); - raw - } else { - // Backslide occurred. We reconstruct monotonized time from the upper 32 bit of the - // passed in value and the 64bits loaded from the atomic - let seconds_lower = old >> 32; - let mut seconds_upper = secs & 0xffff_ffff_0000_0000; - if secs & 0xffff_ffff > seconds_lower { - // Backslide caused the lower 32bit of the seconds part to wrap. - // This must be the case because the seconds part is larger even though - // we are in the backslide branch, i.e. the seconds count should be smaller or equal. - // - // We assume that backslides are smaller than 2^32 seconds - // which means we need to add 1 to the upper half to restore it. - // - // Example: - // most recent observed time: 0xA1_0000_0000_0000_0000u128 - // bits stored in AtomicU64: 0x0000_0000_0000_0000u64 - // backslide by 1s - // caller time is 0xA0_ffff_ffff_0000_0000u128 - // -> we can fix up the upper half time by adding 1 << 32 - seconds_upper = seconds_upper.wrapping_add(0x1_0000_0000); + let updated = mono.fetch_update(Relaxed, Relaxed, |old| { + (old == UNINITIALIZED || packed.wrapping_sub(old) < u64::MAX / 2).then_some(packed) + }); + match updated { + Ok(_) => raw, + Err(newer) => { + // Backslide occurred. We reconstruct monotonized time from the upper 32 bit of the + // passed in value and the 64bits loaded from the atomic + let seconds_lower = newer >> 32; + let mut seconds_upper = secs & 0xffff_ffff_0000_0000; + if secs & 0xffff_ffff > seconds_lower { + // Backslide caused the lower 32bit of the seconds part to wrap. + // This must be the case because the seconds part is larger even though + // we are in the backslide branch, i.e. the seconds count should be smaller or equal. + // + // We assume that backslides are smaller than 2^32 seconds + // which means we need to add 1 to the upper half to restore it. + // + // Example: + // most recent observed time: 0xA1_0000_0000_0000_0000u128 + // bits stored in AtomicU64: 0x0000_0000_0000_0000u64 + // backslide by 1s + // caller time is 0xA0_ffff_ffff_0000_0000u128 + // -> we can fix up the upper half time by adding 1 << 32 + seconds_upper = seconds_upper.wrapping_add(0x1_0000_0000); + } + let secs = seconds_upper | seconds_lower; + let nanos = newer as u32; + ZERO.checked_add_duration(&Duration::new(secs, nanos)).unwrap() } - let secs = seconds_upper | seconds_lower; - let nanos = old as u32; - ZERO.checked_add_duration(&Duration::new(secs, nanos)).unwrap() } } } |