Function enterTask

src/core/stack_switching/stack_state.mjs:60–96

()

 * @private
 */
export function enterTask() {
  // If this is the first task we enter, record the current stack position as
  // the top of the entire stack and leave it alone.
  if (stackTop === undefined) {
    stackTop = stackSave();
    return;
  }
  // Search for a gap in the stack large enough that we feel like sticking a
  // task in it. We search from bottom to top because insertion is cheaper
  // closer to the bottom. (More specifically, if the tasks run a long time then
  // it costs the same no matter where we insert but if they are short lived
  // inserting lower is better).

  // If we make threshold bigger, we will use up more stack space but also copy
  // less stack around. If we make it smaller, we use less stack space but copy
  // more stack.
  const threshold = (taskSizeTotal / taskSizeCount) * 0.8;
  let lastStop = stackStates.at(-1)?.stop;
  for (let idx = stackStates.length - 2; idx >= -1; idx--) {
    const state =
      idx >= 0 ? stackStates[idx] : { start: stackTop, stop: stackTop };
    if (state.start - lastStop > threshold) {
      setStackPosition(state.start);
      return;
    }
    lastStop = state.stop;
  }
  // No large enough gaps found. Last, check if the current stack position is
  // below the bottom used stack position and if so move the stack up. This can
  // happen if a task higher on the stack exited first followed by a task lower
  // on the stack.
  const bottomUsed = stackStates.at(-1)?.start ?? stackTop;
  if (bottomUsed > stackSave()) {
    setStackPosition(bottomUsed);
    return;
  }
}

function evictStackUpTo(stop) {
  let total = 0;