denoland-deno/cli/ops/performance.rs

// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
use super::dispatch_json::{JsonOp, Value};
use crate::state::ThreadSafeState;
use deno::*;

// 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.
pub fn op_now(
  state: &ThreadSafeState,
  _args: Value,
  _zero_copy: Option<PinnedBuf>,
) -> Result<JsonOp, ErrBox> {
  let seconds = state.start_time.elapsed().as_secs();
  let mut subsec_nanos = state.start_time.elapsed().subsec_nanos();
  let reduced_time_precision = 2_000_000; // 2ms in nanoseconds

  // 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.permissions.allows_hrtime() {
    subsec_nanos -= subsec_nanos % reduced_time_precision
  }

  Ok(JsonOp::Sync(json!({
    "seconds": seconds,
    "subsecNanos": subsec_nanos,
  })))
}