denoland-deno/ext/web/timers.rs

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.

//! This module helps deno implement timers and performance APIs.

use deno_core::op2;
use deno_core::OpState;
use std::time::Instant;

pub trait TimersPermission {
  fn allow_hrtime(&mut self) -> bool;
}

impl TimersPermission for deno_permissions::PermissionsContainer {
  #[inline(always)]
  fn allow_hrtime(&mut self) -> bool {
    true
  }
}

pub type StartTime = Instant;

// Returns a milliseconds and nanoseconds subsec
// since the start time of the deno runtime.
// If the High precision flag is not set, the
// nanoseconds are rounded on 2ms.
#[op2(fast)]
pub fn op_now<TP>(state: &mut OpState, #[buffer] buf: &mut [u8])
where
  TP: TimersPermission + 'static,
{
  let start_time = state.borrow::<StartTime>();
  let elapsed = start_time.elapsed();
  let seconds = elapsed.as_secs();
  let mut subsec_nanos = elapsed.subsec_nanos();

  // If the permission is not enabled
  // Round the nano result on 2 milliseconds
  // see: https://developer.mozilla.org/en-US/docs/Web/API/DOMHighResTimeStamp#Reduced_time_precision
  if !state.borrow_mut::<TP>().allow_hrtime() {
    let reduced_time_precision = 2_000_000; // 2ms in nanoseconds
    subsec_nanos -= subsec_nanos % reduced_time_precision;
  }
  if buf.len() < 8 {
    return;
  }
  let buf: &mut [u32] =
    // SAFETY: buffer is at least 8 bytes long.
    unsafe { std::slice::from_raw_parts_mut(buf.as_mut_ptr() as _, 2) };
  buf[0] = seconds as u32;
  buf[1] = subsec_nanos;
}

#[allow(clippy::unused_async)]
#[op2(async(lazy), fast)]
pub async fn op_defer() {}