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If a timer is requested with <=100ms resolution, request the high-res timer. Since the default Windows timer period is 15ms, this means a 100ms timer could fire at 115ms (15% late). We assume that timers longer than 100ms are a reasonable cutoff here. The high-res timers on Windows are still limited. Unfortuntely this means that our shortest duration 4ms timers can still be 25% late, but without a more complex timer system or spinning on the clock itself, we're somewhat bounded by the OS' scheduler itself.
67 lines
2.1 KiB
Rust
67 lines
2.1 KiB
Rust
// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
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#[cfg(target_os = "windows")]
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mod windows {
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use std::marker::PhantomData;
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use std::sync::atomic::AtomicU32;
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pub(crate) struct HrTimerLock {
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pub(super) _unconstructable: PhantomData<()>,
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}
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/// Decrease the reference count of the HR timer on drop.
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impl Drop for HrTimerLock {
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fn drop(&mut self) {
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dec_ref();
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}
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}
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/// Maintains the HR timer refcount. This should be more than sufficient as 2^32 timers would be
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/// an impossible situation, and if it does somehow happen, the worst case is that we'll disable
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/// the high-res timer when we shouldn't (and things would eventually return to proper operation).
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static TIMER_REFCOUNT: AtomicU32 = AtomicU32::new(0);
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pub(super) fn inc_ref() {
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let old = TIMER_REFCOUNT.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
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// Overflow/underflow sanity check in debug mode
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debug_assert!(old != u32::MAX);
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if old == 0 {
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lock_hr();
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}
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}
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fn dec_ref() {
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let old = TIMER_REFCOUNT.fetch_sub(1, std::sync::atomic::Ordering::SeqCst);
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// Overflow/underflow sanity check in debug mode
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debug_assert!(old != 0);
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if old == 1 {
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unlock_hr();
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}
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}
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/// If the refcount is > 0, we ask Windows for a lower timer period once. While the underlying
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/// Windows timeBeginPeriod/timeEndPeriod API can manage its own reference counts, we choose to
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/// use it once per process and avoid nesting these calls.
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fn lock_hr() {
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// SAFETY: We just want to set the timer period here
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unsafe { windows_sys::Win32::Media::timeBeginPeriod(1) };
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}
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fn unlock_hr() {
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// SAFETY: We just want to set the timer period here
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unsafe { windows_sys::Win32::Media::timeEndPeriod(1) };
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}
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}
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#[cfg(target_os = "windows")]
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pub(crate) fn hr_timer_lock() -> windows::HrTimerLock {
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windows::inc_ref();
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windows::HrTimerLock {
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_unconstructable: Default::default(),
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}
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}
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/// No-op on other platforms.
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#[cfg(not(target_os = "windows"))]
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pub(crate) fn hr_timer_lock() -> (std::marker::PhantomData<()>,) {
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(std::marker::PhantomData::default(),)
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}
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