从定时器堆确定等待时间，再集中执行到期回调

37static int timer_less_than(const struct heap_node* ha,38                           const struct heap_node* hb) {39  const uv_timer_t* a;40  const uv_timer_t* b;4142  a = container_of(ha, uv_timer_t, node.heap);43  b = container_of(hb, uv_timer_t, node.heap);4445  if (a->timeout < b->timeout)46    return 1;47  if (b->timeout < a->timeout)48    return 0;4950  /* Compare start_id when both have the same timeout. start_id is51   * allocated with loop->timer_counter in uv_timer_start().52   */53  return a->start_id < b->start_id;54}

76  uv_timer_stop(handle);7778  clamped_timeout = handle->loop->time + timeout;79  if (clamped_timeout < timeout)80    clamped_timeout = (uint64_t) -1;8182  handle->timer_cb = cb;83  handle->timeout = clamped_timeout;84  handle->repeat = repeat;85  /* start_id is the second index to be compared in timer_less_than() */86  handle->start_id = handle->loop->timer_counter++;8788  heap_insert(timer_heap(handle->loop),89              (struct heap_node*) &handle->node.heap,90              timer_less_than);91  uv__handle_start(handle);9293  return 0;

127  parent = child = &heap->min;128  while (k > 0) {129    parent = child;130    if (path & 1)131      child = &(*child)->right;132    else133      child = &(*child)->left;134    path >>= 1;135    k -= 1;136  }137138  /* Insert the new node. */139  newnode->parent = *parent;140  *child = newnode;141  heap->nelts += 1;142143  /* Walk up the tree and check at each node if the heap property holds.144   * It's a min heap so parent < child must be true.145   */146  while (newnode->parent != NULL && less_than(newnode, newnode->parent))147    heap_node_swap(heap, newnode->parent, newnode);148}

143int uv__next_timeout(const uv_loop_t* loop) {144  const struct heap_node* heap_node;145  const uv_timer_t* handle;146  uint64_t diff;147148  heap_node = heap_min(timer_heap(loop));149  if (heap_node == NULL)150    return -1; /* block indefinitely */151152  handle = container_of(heap_node, uv_timer_t, node.heap);153  if (handle->timeout <= loop->time)154    return 0;155156  diff = handle->timeout - loop->time;157  if (diff > INT_MAX)158    diff = INT_MAX;159160  return (int) diff;

172  for (;;) {173    heap_node = heap_min(timer_heap(loop));174    if (heap_node == NULL)175      break;176177    handle = container_of(heap_node, uv_timer_t, node.heap);178    if (handle->timeout > loop->time)179      break;180181    uv_timer_stop(handle);182    uv__queue_insert_tail(&ready_queue, &handle->node.queue);183  }184185  while (!uv__queue_empty(&ready_queue)) {186    queue_node = uv__queue_head(&ready_queue);187    uv__queue_remove(queue_node);188    uv__queue_init(queue_node);189    handle = container_of(queue_node, uv_timer_t, node.queue);190191    uv_timer_again(handle);192    handle->timer_cb(handle);193  }

403static int uv__backend_timeout(const uv_loop_t* loop) {404  if (loop->stop_flag == 0 &&405      /* uv__loop_alive(loop) && */406      (uv__has_active_handles(loop) || uv__has_active_reqs(loop)) &&407      uv__queue_empty(&loop->pending_queue) &&408      uv__queue_empty(&loop->idle_handles) &&409      (loop->flags & UV_LOOP_REAP_CHILDREN) == 0 &&410      loop->closing_handles == NULL)411    return uv__next_timeout(loop);412  return 0;413}