req: revisions to uv_req_t handling

- Remove the `active_reqs` queue, which is never used. There are more
   efficient per-stream queues that `libuv` uses whenever it needs this
   information, so duplicating it and managing it here seems
   like unnecessary extra space and work.
 - Unix `uv_loop_init` didn't explicitly initialize.
   `loop->active_handles` (although it did memset the whole struct
   to 0, so it wasn't wrong previously, just inconsistent).
 - Consolidate repeated code for `uv__has_active_reqs`.
 - Change `uv__loop_alive` to use the helper functions (mirroring the
   unix copy of the same function).
 - Initialize some more uv_stream_t fields in init, rather than waiting
   for the connection callback. This helps surface bugs in libuv or the
   caller better, since it ensures libuv doesn't see uninitialized
   memory if asked to look at these fields before it thinks the socket
   is connected.
 - Fixes what appears to be a double-counting of `handle->reqs_pending`,
   in the highly-unlikely event that the code wants to emulate IOCP,
   but `RegisterWaitForSingleObject` somehow managed to fail.

PR-URL: https://github.com/libuv/libuv/pull/1746
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

include/uv.h

@@ -378,8 +378,7 @@ UV_EXTERN const char* uv_err_name(int err);
   /* read-only */                                                             \
   uv_req_type type;                                                           \
   /* private */                                                               \
-  void* active_queue[2];                                                      \
-  void* reserved[4];                                                          \
+  void* reserved[6];                                                          \
   UV_REQ_PRIVATE_FIELDS                                                       \
 
 /* Abstract base class of all requests. */
@@ -1531,7 +1530,10 @@ struct uv_loop_s {
   /* Loop reference counting. */
   unsigned int active_handles;
   void* handle_queue[2];
-  void* active_reqs[2];
+  union {
+    void* unused[2];
+    unsigned int count;
+  } active_reqs;
   /* Internal flag to signal loop stop. */
   unsigned int stop_flag;
   UV_LOOP_PRIVATE_FIELDS

src/unix/loop.c

@@ -38,13 +38,14 @@ int uv_loop_init(uv_loop_t* loop) {
 
   heap_init((struct heap*) &loop->timer_heap);
   QUEUE_INIT(&loop->wq);
-  QUEUE_INIT(&loop->active_reqs);
   QUEUE_INIT(&loop->idle_handles);
   QUEUE_INIT(&loop->async_handles);
   QUEUE_INIT(&loop->check_handles);
   QUEUE_INIT(&loop->prepare_handles);
   QUEUE_INIT(&loop->handle_queue);
 
+  loop->active_handles = 0;
+  loop->active_reqs.count = 0;
   loop->nfds = 0;
   loop->watchers = NULL;
   loop->nwatchers = 0;

src/uv-common.c

@@ -627,7 +627,7 @@ int uv_loop_close(uv_loop_t* loop) {
   void* saved_data;
 #endif
 
-  if (!QUEUE_EMPTY(&(loop)->active_reqs))
+  if (uv__has_active_reqs(loop))
     return UV_EBUSY;
 
   QUEUE_FOREACH(q, &loop->handle_queue) {

src/uv-common.h

@@ -133,18 +133,18 @@ int uv__socket_sockopt(uv_handle_t* handle, int optname, int* value);
 void uv__fs_scandir_cleanup(uv_fs_t* req);
 
 #define uv__has_active_reqs(loop)                                             \
-  (QUEUE_EMPTY(&(loop)->active_reqs) == 0)
+  ((loop)->active_reqs.count > 0)
 
 #define uv__req_register(loop, req)                                           \
   do {                                                                        \
-    QUEUE_INSERT_TAIL(&(loop)->active_reqs, &(req)->active_queue);            \
+    (loop)->active_reqs.count++;                                              \
   }                                                                           \
   while (0)
 
 #define uv__req_unregister(loop, req)                                         \
   do {                                                                        \
     assert(uv__has_active_reqs(loop));                                        \
-    QUEUE_REMOVE(&(req)->active_queue);                                       \
+    (loop)->active_reqs.count--;                                              \
   }                                                                           \
   while (0)
 

src/win/core.c

@@ -239,7 +239,7 @@ int uv_loop_init(uv_loop_t* loop) {
 
   QUEUE_INIT(&loop->wq);
   QUEUE_INIT(&loop->handle_queue);
-  QUEUE_INIT(&loop->active_reqs);
+  loop->active_reqs.count = 0;
   loop->active_handles = 0;
 
   loop->pending_reqs_tail = NULL;
@@ -470,8 +470,8 @@ static void uv_poll_ex(uv_loop_t* loop, DWORD timeout) {
 
 
 static int uv__loop_alive(const uv_loop_t* loop) {
-  return loop->active_handles > 0 ||
-         !QUEUE_EMPTY(&loop->active_reqs) ||
+  return uv__has_active_handles(loop) ||
+         uv__has_active_reqs(loop) ||
          loop->endgame_handles != NULL;
 }
 

src/win/pipe.c

@@ -847,6 +847,7 @@ static void uv_pipe_queue_accept(uv_loop_t* loop, uv_pipe_t* handle,
     return;
   }
 
+  /* Wait for completion via IOCP */
   handle->reqs_pending++;
 }
 

src/win/stream-inl.h

@@ -37,11 +37,6 @@ INLINE static void uv_stream_init(uv_loop_t* loop,
   handle->write_queue_size = 0;
   handle->activecnt = 0;
   handle->stream.conn.shutdown_req = NULL;
-}
-
-
-INLINE static void uv_connection_init(uv_stream_t* handle) {
-  handle->flags |= UV_HANDLE_CONNECTION;
   handle->stream.conn.write_reqs_pending = 0;
 
   UV_REQ_INIT(&handle->read_req, UV_READ);
@@ -51,4 +46,9 @@ INLINE static void uv_connection_init(uv_stream_t* handle) {
 }
 
 
+INLINE static void uv_connection_init(uv_stream_t* handle) {
+  handle->flags |= UV_HANDLE_CONNECTION;
+}
+
+
 #endif /* UV_WIN_STREAM_INL_H_ */

src/win/tcp.c

@@ -459,8 +459,6 @@ static void uv_tcp_queue_accept(uv_tcp_t* handle, uv_tcp_accept_t* req) {
           INFINITE, WT_EXECUTEINWAITTHREAD)) {
       SET_REQ_ERROR(req, GetLastError());
       uv_insert_pending_req(loop, (uv_req_t*)req);
-      handle->reqs_pending++;
-      return;
     }
   } else {
     /* Make this req pending reporting an error. */