unix, windows: run expired timers in run-once mode

Before this commit, creating an event loop, starting a timer and
calling uv_run(UV_RUN_ONCE) blocked in uv_run() until the timer
expired - but didn't actually run the timer.

src/unix/core.c

@@ -317,8 +317,21 @@ int uv_run(uv_loop_t* loop, uv_run_mode mode) {
     uv__io_poll(loop, timeout);
     uv__run_check(loop);
     uv__run_closing_handles(loop);
-    r = uv__loop_alive(loop);
 
+    if (mode == UV_RUN_ONCE) {
+      /* UV_RUN_ONCE implies forward progess: at least one callback must have
+       * been invoked when it returns. uv__io_poll() can return without doing
+       * I/O (meaning: no callbacks) when its timeout expires - which means we
+       * have pending timers that satisfy the forward progress constraint.
+       *
+       * UV_RUN_NOWAIT makes no guarantees about progress so it's omitted from
+       * the check.
+       */
+      uv__update_time(loop);
+      uv__run_timers(loop);
+    }
+
+    r = uv__loop_alive(loop);
     UV_TICK_STOP(loop, mode);
 
     if (mode & (UV_RUN_ONCE | UV_RUN_NOWAIT))

src/win/core.c

@@ -298,6 +298,20 @@ int uv_run(uv_loop_t *loop, uv_run_mode mode) {
                   !(mode & UV_RUN_NOWAIT));
 
     uv_check_invoke(loop);
+
+    if (mode == UV_RUN_ONCE) {
+      /* UV_RUN_ONCE implies forward progess: at least one callback must have
+       * been invoked when it returns. uv__io_poll() can return without doing
+       * I/O (meaning: no callbacks) when its timeout expires - which means we
+       * have pending timers that satisfy the forward progress constraint.
+       *
+       * UV_RUN_NOWAIT makes no guarantees about progress so it's omitted from
+       * the check.
+       */
+      uv_update_time(loop);
+      uv_process_timers(loop);
+    }
+
     r = uv__loop_alive(loop);
     if (mode & (UV_RUN_ONCE | UV_RUN_NOWAIT))
       break;

test/test-list.h

@@ -101,6 +101,7 @@ TEST_DECLARE   (timer_start_twice)
 TEST_DECLARE   (timer_order)
 TEST_DECLARE   (timer_huge_timeout)
 TEST_DECLARE   (timer_huge_repeat)
+TEST_DECLARE   (timer_run_once)
 TEST_DECLARE   (idle_starvation)
 TEST_DECLARE   (loop_handles)
 TEST_DECLARE   (get_loadavg)
@@ -350,6 +351,7 @@ TASK_LIST_START
   TEST_ENTRY  (timer_order)
   TEST_ENTRY  (timer_huge_timeout)
   TEST_ENTRY  (timer_huge_repeat)
+  TEST_ENTRY  (timer_run_once)
 
   TEST_ENTRY  (idle_starvation)
 

test/test-timer.c

@@ -264,3 +264,31 @@ TEST_IMPL(timer_huge_repeat) {
   MAKE_VALGRIND_HAPPY();
   return 0;
 }
+
+
+static unsigned int timer_run_once_timer_cb_called;
+
+
+static void timer_run_once_timer_cb(uv_timer_t* handle, int status) {
+  timer_run_once_timer_cb_called++;
+}
+
+
+TEST_IMPL(timer_run_once) {
+  uv_timer_t timer_handle;
+
+  ASSERT(0 == uv_timer_init(uv_default_loop(), &timer_handle));
+  ASSERT(0 == uv_timer_start(&timer_handle, timer_run_once_timer_cb, 0, 0));
+  ASSERT(0 == uv_run(uv_default_loop(), UV_RUN_ONCE));
+  ASSERT(1 == timer_run_once_timer_cb_called);
+
+  ASSERT(0 == uv_timer_start(&timer_handle, timer_run_once_timer_cb, 1, 0));
+  ASSERT(0 == uv_run(uv_default_loop(), UV_RUN_ONCE));
+  ASSERT(2 == timer_run_once_timer_cb_called);
+
+  uv_close((uv_handle_t*) &timer_handle, NULL);
+  ASSERT(0 == uv_run(uv_default_loop(), UV_RUN_ONCE));
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}