Function acquireBuildSlot

apps/cloud/src/mcp/session-build-semaphore.ts:87–154

(maxQueueWaitMs: number = MAX_QUEUE_WAIT_MS)

 * anymore.
 */
export const acquireBuildSlot = (maxQueueWaitMs: number = MAX_QUEUE_WAIT_MS): BuildSlotHandle => {
  const requestedAt = Date.now();

  if (activeBuilds < MAX_CONCURRENT_BUILDS) {
    activeBuilds += 1;
    let released = false;
    return {
      promise: Promise.resolve({ acquired: true, waitMs: 0, timedOut: false }),
      cancel: () => {
        if (released) return;
        released = true;
        releaseBuildSlot();
      },
    };
  }

  let resolvePromise!: (value: BuildSlotResult) => void;
  const promise = new Promise<BuildSlotResult>((resolve) => {
    resolvePromise = resolve;
  });

  const waiter: Waiter = {
    state: "queued",
    grant: () => {
      // Guaranteed "queued" here: `releaseBuildSlot` only reaches a waiter by
      // shifting it out of `waitQueue`, and both other transitions
      // (timeout, cancel) remove the waiter from the queue in the same tick
      // they change its state, so a granted waiter can't have been anything
      // else.
      waiter.state = "granted";
      activeBuilds += 1;
      resolvePromise({ acquired: true, waitMs: Date.now() - requestedAt, timedOut: false });
    },
  };
  waitQueue.push(waiter);

  const timer = setTimeout(() => {
    if (waiter.state !== "queued") return;
    waiter.state = "timed-out";
    const idx = waitQueue.indexOf(waiter);
    if (idx !== -1) waitQueue.splice(idx, 1);
    resolvePromise({ acquired: false, waitMs: Date.now() - requestedAt, timedOut: true });
  }, maxQueueWaitMs);

  return {
    promise,
    cancel: () => {
      clearTimeout(timer);
      if (waiter.state === "queued") {
        waiter.state = "cancelled";
        const idx = waitQueue.indexOf(waiter);
        if (idx !== -1) waitQueue.splice(idx, 1);
        return;
      }
      if (waiter.state === "granted") {
        // Grant already happened (raced with a concurrent `releaseBuildSlot`
        // shifting this waiter off the queue) before this cancel ran, and
        // the caller never got to consume the slot — hand it back now