deno/ext/web/hr_timer_lock.rs
2023-07-13 15:16:24 -06:00

67 lines
2.1 KiB
Rust

// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
#[cfg(target_os = "windows")]
mod windows {
use std::marker::PhantomData;
use std::sync::atomic::AtomicU32;
pub(crate) struct HrTimerLock {
pub(super) _unconstructable: PhantomData<()>,
}
/// Decrease the reference count of the HR timer on drop.
impl Drop for HrTimerLock {
fn drop(&mut self) {
dec_ref();
}
}
/// Maintains the HR timer refcount. This should be more than sufficient as 2^32 timers would be
/// an impossible situation, and if it does somehow happen, the worst case is that we'll disable
/// the high-res timer when we shouldn't (and things would eventually return to proper operation).
static TIMER_REFCOUNT: AtomicU32 = AtomicU32::new(0);
pub(super) fn inc_ref() {
let old = TIMER_REFCOUNT.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
// Overflow/underflow sanity check in debug mode
debug_assert!(old != u32::MAX);
if old == 0 {
lock_hr();
}
}
fn dec_ref() {
let old = TIMER_REFCOUNT.fetch_sub(1, std::sync::atomic::Ordering::SeqCst);
// Overflow/underflow sanity check in debug mode
debug_assert!(old != 0);
if old == 1 {
unlock_hr();
}
}
/// If the refcount is > 0, we ask Windows for a lower timer period once. While the underlying
/// Windows timeBeginPeriod/timeEndPeriod API can manage its own reference counts, we choose to
/// use it once per process and avoid nesting these calls.
fn lock_hr() {
// SAFETY: We just want to set the timer period here
unsafe { windows_sys::Win32::Media::timeBeginPeriod(1) };
}
fn unlock_hr() {
// SAFETY: We just want to set the timer period here
unsafe { windows_sys::Win32::Media::timeEndPeriod(1) };
}
}
#[cfg(target_os = "windows")]
pub(crate) fn hr_timer_lock() -> windows::HrTimerLock {
windows::inc_ref();
windows::HrTimerLock {
_unconstructable: Default::default(),
}
}
/// No-op on other platforms.
#[cfg(not(target_os = "windows"))]
pub(crate) fn hr_timer_lock() -> (std::marker::PhantomData<()>,) {
Default::default()
}