unix, windows: allow NULL async callback

Allow a NULL callback so the user doesn't have to provide a dummy when
the actual event is processed by e.g. a check handle callback.

Makefile.am

@@ -63,6 +63,7 @@ test_run_tests_SOURCES = test/blackhole-server.c \
                          test/task.h \
                          test/test-active.c \
                          test/test-async.c \
+                         test/test-async-null-cb.c \
                          test/test-barrier.c \
                          test/test-callback-order.c \
                          test/test-callback-stack.c \

include/uv.h

@@ -1239,6 +1239,12 @@ struct uv_async_s {
   UV_ASYNC_PRIVATE_FIELDS
 };
 
+/*
+ * Initialize the uv_async_t handle. A NULL callback is allowed.
+ *
+ * Note that uv_async_init(), unlike other libuv functions, immediately
+ * starts the handle. To stop the handle again, close it with uv_close().
+ */
 UV_EXTERN int uv_async_init(uv_loop_t*, uv_async_t* async,
     uv_async_cb async_cb);
 

src/unix/async.c

@@ -78,8 +78,13 @@ static void uv__async_event(uv_loop_t* loop,
 
   QUEUE_FOREACH(q, &loop->async_handles) {
     h = QUEUE_DATA(q, uv_async_t, queue);
-    if (!h->pending) continue;
+
+    if (h->pending == 0)
+      continue;
     h->pending = 0;
+
+    if (h->async_cb == NULL)
+      continue;
     h->async_cb(h, 0);
   }
 }

src/win/async.c

@@ -91,9 +91,9 @@ void uv_process_async_wakeup_req(uv_loop_t* loop, uv_async_t* handle,
 
   handle->async_sent = 0;
 
-  if (!(handle->flags & UV__HANDLE_CLOSING)) {
-    handle->async_cb((uv_async_t*) handle, 0);
-  } else {
+  if (handle->flags & UV__HANDLE_CLOSING) {
     uv_want_endgame(loop, (uv_handle_t*)handle);
+  } else if (handle->async_cb != NULL) {
+    handle->async_cb(handle, 0);
   }
 }

test/test-async-null-cb.c

@@ -0,0 +1,55 @@
+/* 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_async_t async_handle;
+static uv_check_t check_handle;
+static int check_cb_called;
+static uv_thread_t thread;
+
+
+static void thread_cb(void* dummy) {
+  (void) &dummy;
+  uv_async_send(&async_handle);
+}
+
+
+static void check_cb(uv_check_t* handle, int status) {
+  ASSERT(check_cb_called == 0);
+  uv_close((uv_handle_t*) &async_handle, NULL);
+  uv_close((uv_handle_t*) &check_handle, NULL);
+  check_cb_called++;
+}
+
+
+TEST_IMPL(async_null_cb) {
+  ASSERT(0 == uv_async_init(uv_default_loop(), &async_handle, NULL));
+  ASSERT(0 == uv_check_init(uv_default_loop(), &check_handle));
+  ASSERT(0 == uv_check_start(&check_handle, check_cb));
+  ASSERT(0 == uv_thread_create(&thread, thread_cb, NULL));
+  ASSERT(0 == uv_run(uv_default_loop(), UV_RUN_DEFAULT));
+  ASSERT(0 == uv_thread_join(&thread));
+  ASSERT(1 == check_cb_called);
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}

test/test-list.h

@@ -134,6 +134,7 @@ TEST_DECLARE   (has_ref)
 TEST_DECLARE   (active)
 TEST_DECLARE   (embed)
 TEST_DECLARE   (async)
+TEST_DECLARE   (async_null_cb)
 TEST_DECLARE   (get_currentexe)
 TEST_DECLARE   (process_title)
 TEST_DECLARE   (cwd_and_chdir)
@@ -396,6 +397,7 @@ TASK_LIST_START
   TEST_ENTRY  (embed)
 
   TEST_ENTRY  (async)
+  TEST_ENTRY  (async_null_cb)
 
   TEST_ENTRY  (get_currentexe)
 

uv.gyp

@@ -302,6 +302,7 @@
         'test/test-util.c',
         'test/test-active.c',
         'test/test-async.c',
+        'test/test-async-null-cb.c',
         'test/test-callback-stack.c',
         'test/test-callback-order.c',
         'test/test-connection-fail.c',