src: don't run timers before entering event loop (#4026)

There should be no need to run timers prior to entering the event loop.
Instead allow them to run normally at the end after the poll phase is
complete.

Ref: https://github.com/libuv/libuv/pull/3927
Ref: https://github.com/libuv/libuv/issues/4017

docs/src/design.rst

@@ -62,9 +62,6 @@ stages of a loop iteration:
 
 #. The loop concept of 'now' is initially set.
 
-#. Due timers are run if the loop was run with ``UV_RUN_DEFAULT``. All active timers scheduled
-   for a time before the loop's concept of *now* get their callbacks called.
-
 #. If the loop is *alive*  an iteration is started, otherwise the loop will exit immediately. So,
    when is a loop considered to be *alive*? If a loop has active and ref'd handles, active
    requests or closing handles it's considered to be *alive*.

src/unix/core.c

@@ -411,16 +411,6 @@ int uv_run(uv_loop_t* loop, uv_run_mode mode) {
   if (!r)
     uv__update_time(loop);
 
-  /* Maintain backwards compatibility by processing timers before entering the
-   * while loop for UV_RUN_DEFAULT. Otherwise timers only need to be executed
-   * once, which should be done after polling in order to maintain proper
-   * execution order of the conceptual event loop. */
-  if (mode == UV_RUN_DEFAULT) {
-    if (r)
-      uv__update_time(loop);
-    uv__run_timers(loop);
-  }
-
   while (r != 0 && loop->stop_flag == 0) {
     can_sleep =
         QUEUE_EMPTY(&loop->pending_queue) && QUEUE_EMPTY(&loop->idle_handles);

src/win/core.c

@@ -497,16 +497,6 @@ int uv_run(uv_loop_t *loop, uv_run_mode mode) {
   if (!r)
     uv_update_time(loop);
 
-  /* Maintain backwards compatibility by processing timers before entering the
-   * while loop for UV_RUN_DEFAULT. Otherwise timers only need to be executed
-   * once, which should be done after polling in order to maintain proper
-   * execution order of the conceptual event loop. */
-  if (mode == UV_RUN_DEFAULT) {
-    if (r)
-      uv_update_time(loop);
-    uv__run_timers(loop);
-  }
-
   while (r != 0 && loop->stop_flag == 0) {
     can_sleep = loop->pending_reqs_tail == NULL && QUEUE_EMPTY(&loop->idle_handles);
 

test/test-close-order.c

@@ -40,7 +40,7 @@ static void close_cb(uv_handle_t* handle) {
 /* check_cb should run before any close_cb */
 static void check_cb(uv_check_t* handle) {
   ASSERT(check_cb_called == 0);
-  ASSERT(timer_cb_called == 1);
+  ASSERT(timer_cb_called == 0);
   ASSERT(close_cb_called == 0);
   uv_close((uv_handle_t*) handle, close_cb);
   uv_close((uv_handle_t*) &timer_handle2, close_cb);