unix, windows: add uv_loop_alive() function

Useful to know when the the event loop is empty, this can't be done with
uv_run() without possibly blocking, or running some events (which might
empty the event loop as a side-effect).

Makefile.am

@@ -145,6 +145,7 @@ test_run_tests_SOURCES = test/blackhole-server.c \
                          test/test-ipc.c \
                          test/test-list.h \
                          test/test-loop-handles.c \
+                         test/test-loop-alive.c \
                          test/test-loop-stop.c \
                          test/test-loop-time.c \
                          test/test-multiple-listen.c \

include/uv.h

@@ -272,6 +272,12 @@ UV_EXTERN uv_loop_t* uv_default_loop(void);
  */
 UV_EXTERN int uv_run(uv_loop_t*, uv_run_mode mode);
 
+/*
+ * This function checks whether the reference count, the number of active
+ * handles or requests left in the event loop, is non-zero.
+ */
+UV_EXTERN int uv_loop_alive(const uv_loop_t* loop);
+
 /*
  * This function will stop the event loop by forcing uv_run to end
  * as soon as possible, but not sooner than the next loop iteration.

src/unix/core.c

@@ -248,13 +248,18 @@ int uv_backend_timeout(const uv_loop_t* loop) {
 }
 
 
-static int uv__loop_alive(uv_loop_t* loop) {
+static int uv__loop_alive(const uv_loop_t* loop) {
   return uv__has_active_handles(loop) ||
          uv__has_active_reqs(loop) ||
          loop->closing_handles != NULL;
 }
 
 
+int uv_loop_alive(const uv_loop_t* loop) {
+    return uv__loop_alive(loop);
+}
+
+
 int uv_run(uv_loop_t* loop, uv_run_mode mode) {
   int timeout;
   int r;

src/win/core.c

@@ -256,13 +256,18 @@ static void uv_poll_ex(uv_loop_t* loop, int block) {
 }
 
 
-static int uv__loop_alive(uv_loop_t* loop) {
+static int uv__loop_alive(const uv_loop_t* loop) {
   return loop->active_handles > 0 ||
          !QUEUE_EMPTY(&loop->active_reqs) ||
          loop->endgame_handles != NULL;
 }
 
 
+int uv_loop_alive(const uv_loop_t* loop) {
+    return uv__loop_alive(loop);
+}
+
+
 int uv_run(uv_loop_t *loop, uv_run_mode mode) {
   int r;
   void (*poll)(uv_loop_t* loop, int block);

test/test-list.h

@@ -24,6 +24,7 @@ TEST_DECLARE   (callback_order)
 TEST_DECLARE   (close_order)
 TEST_DECLARE   (run_once)
 TEST_DECLARE   (run_nowait)
+TEST_DECLARE   (loop_alive)
 TEST_DECLARE   (loop_stop)
 TEST_DECLARE   (loop_update_time)
 TEST_DECLARE   (barrier_1)
@@ -253,6 +254,7 @@ TASK_LIST_START
   TEST_ENTRY  (close_order)
   TEST_ENTRY  (run_once)
   TEST_ENTRY  (run_nowait)
+  TEST_ENTRY  (loop_alive)
   TEST_ENTRY  (loop_stop)
   TEST_ENTRY  (loop_update_time)
   TEST_ENTRY  (barrier_1)

test/test-loop-alive.c

@@ -0,0 +1,68 @@
+/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "uv.h"
+#include "task.h"
+
+static uv_timer_t timer_handle;
+
+static void timer_cb(uv_timer_t* handle, int status) {
+  ASSERT(handle);
+  ASSERT(status == 0);
+}
+
+
+static uv_work_t work_req;
+
+static void work_cb(uv_work_t* req) {
+  ASSERT(req);
+}
+
+static void after_work_cb(uv_work_t* req, int status) {
+  ASSERT(req);
+  ASSERT(status == 0);
+}
+
+
+TEST_IMPL(loop_alive) {
+  int r;
+  ASSERT(!uv_loop_alive(uv_default_loop()));
+
+  /* loops with handles are alive */
+  uv_timer_init(uv_default_loop(), &timer_handle);
+  uv_timer_start(&timer_handle, timer_cb, 100, 0);
+  ASSERT(uv_loop_alive(uv_default_loop()));
+
+  r = uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+  ASSERT(r == 0);
+  ASSERT(!uv_loop_alive(uv_default_loop()));
+
+  /* loops with requests are alive */
+  r = uv_queue_work(uv_default_loop(), &work_req, work_cb, after_work_cb);
+  ASSERT(r == 0);
+  ASSERT(uv_loop_alive(uv_default_loop()));
+
+  r = uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+  ASSERT(r == 0);
+  ASSERT(!uv_loop_alive(uv_default_loop()));
+
+  return 0;
+}

uv.gyp

@@ -323,6 +323,7 @@
         'test/test-ipc-send-recv.c',
         'test/test-list.h',
         'test/test-loop-handles.c',
+        'test/test-loop-alive.c',
         'test/test-loop-stop.c',
         'test/test-loop-time.c',
         'test/test-walk-handles.c',