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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.
109 lines
3.3 KiB
Rust
109 lines
3.3 KiB
Rust
// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
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//! This module helps deno implement timers and performance APIs.
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use crate::hr_timer_lock::hr_timer_lock;
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use deno_core::error::AnyError;
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use deno_core::op;
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use deno_core::CancelFuture;
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use deno_core::CancelHandle;
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use deno_core::OpState;
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use deno_core::Resource;
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use deno_core::ResourceId;
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use std::borrow::Cow;
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use std::cell::RefCell;
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use std::rc::Rc;
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use std::time::Duration;
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use std::time::Instant;
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pub trait TimersPermission {
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fn allow_hrtime(&mut self) -> bool;
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fn check_unstable(&self, state: &OpState, api_name: &'static str);
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}
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pub type StartTime = Instant;
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// Returns a milliseconds and nanoseconds subsec
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// since the start time of the deno runtime.
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// If the High precision flag is not set, the
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// nanoseconds are rounded on 2ms.
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#[op(fast)]
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pub fn op_now<TP>(state: &mut OpState, buf: &mut [u8])
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where
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TP: TimersPermission + 'static,
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{
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let start_time = state.borrow::<StartTime>();
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let elapsed = start_time.elapsed();
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let seconds = elapsed.as_secs();
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let mut subsec_nanos = elapsed.subsec_nanos();
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// If the permission is not enabled
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// Round the nano result on 2 milliseconds
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// see: https://developer.mozilla.org/en-US/docs/Web/API/DOMHighResTimeStamp#Reduced_time_precision
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if !state.borrow_mut::<TP>().allow_hrtime() {
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let reduced_time_precision = 2_000_000; // 2ms in nanoseconds
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subsec_nanos -= subsec_nanos % reduced_time_precision;
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}
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if buf.len() < 8 {
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return;
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}
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let buf: &mut [u32] =
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// SAFETY: buffer is at least 8 bytes long.
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unsafe { std::slice::from_raw_parts_mut(buf.as_mut_ptr() as _, 2) };
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buf[0] = seconds as u32;
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buf[1] = subsec_nanos;
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}
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pub struct TimerHandle(Rc<CancelHandle>);
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impl Resource for TimerHandle {
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fn name(&self) -> Cow<str> {
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"timer".into()
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}
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fn close(self: Rc<Self>) {
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self.0.cancel();
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}
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}
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/// Creates a [`TimerHandle`] resource that can be used to cancel invocations of
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/// [`op_sleep`].
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#[op]
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pub fn op_timer_handle(state: &mut OpState) -> ResourceId {
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state
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.resource_table
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.add(TimerHandle(CancelHandle::new_rc()))
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}
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/// Waits asynchronously until either `millis` milliseconds have passed or the
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/// [`TimerHandle`] resource given by `rid` has been canceled.
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///
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/// If the timer is canceled, this returns `false`. Otherwise, it returns `true`.
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#[op(deferred)]
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pub async fn op_sleep(
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state: Rc<RefCell<OpState>>,
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millis: u64,
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rid: ResourceId,
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) -> Result<bool, AnyError> {
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let handle = state.borrow().resource_table.get::<TimerHandle>(rid)?;
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// If a timer is requested with <=100ms resolution, request the high-res timer. Since the default
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// Windows timer period is 15ms, this means a 100ms timer could fire at 115ms (15% late). We assume that
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// timers longer than 100ms are a reasonable cutoff here.
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// The high-res timers on Windows are still limited. Unfortuntely this means that our shortest duration 4ms timers
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// can still be 25% late, but without a more complex timer system or spinning on the clock itself, we're somewhat
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// bounded by the OS' scheduler itself.
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let _hr_timer_lock = if millis <= 100 {
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Some(hr_timer_lock())
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} else {
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None
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};
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let res = tokio::time::sleep(Duration::from_millis(millis))
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.or_cancel(handle.0.clone())
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.await;
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// We release the high-res timer lock here, either by being cancelled or resolving.
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Ok(res.is_ok())
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}
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