loop_close: close all handles

- Move uv_stop(), it still causes a "leak" on exit somehow.
- Tenatively restore `UV_RUN_DEFAULT`.  It shouldn't hang since we
  clobber the handles via `uv_walk((h)=>uv_close(h))`. Although this
  still "leaks" on exit, it's faster than the 2-second timeout.

fix neovim#11820
fix neovim#7376

src/nvim/event/loop.c

@@ -116,6 +116,15 @@ void loop_on_put(MultiQueue *queue, void *data)
   uv_stop(&loop->uv);
 }
 
+#if !defined(EXITFREE)
+static void loop_walk_cb(uv_handle_t *handle, void *arg)
+{
+  if (!uv_is_closing(handle)) {
+    uv_close(handle, NULL);
+  }
+}
+#endif
+
 /// Closes `loop` and its handles, and frees its structures.
 ///
 /// @param loop  Loop to destroy
@@ -125,21 +134,17 @@ void loop_on_put(MultiQueue *queue, void *data)
 bool loop_close(Loop *loop, bool wait)
 {
   bool rv = true;
-  // Loop won’t block for I/O after this.
-  uv_stop(&loop->uv);
-  // TODO(justinmk): Close all (lua/luv!) handles. But walk_cb() needs to call
-  // the resource-specific close-callbacks...
-  //    uv_walk((h) => { if !uv_is_closing(h) { uv_close(h, …) } })
   uv_mutex_destroy(&loop->mutex);
   uv_close((uv_handle_t *)&loop->children_watcher, NULL);
   uv_close((uv_handle_t *)&loop->children_kill_timer, NULL);
   uv_close((uv_handle_t *)&loop->poll_timer, timer_close_cb);
   uv_close((uv_handle_t *)&loop->async, NULL);
   uint64_t start = wait ? os_hrtime() : 0;
+  bool didstop = false;
   while (true) {
     // Run the loop to tickle close-callbacks (which should then free memory).
     // Use UV_RUN_NOWAIT to avoid a hang. #11820
-    uv_run(&loop->uv, UV_RUN_NOWAIT);
+    uv_run(&loop->uv, didstop ? UV_RUN_DEFAULT : UV_RUN_NOWAIT);
     if ((uv_loop_close(&loop->uv) != UV_EBUSY) || !wait) {
       break;
     }
@@ -151,6 +156,18 @@ bool loop_close(Loop *loop, bool wait)
       log_uv_handles(&loop->uv);
       break;
     }
+#if defined(EXITFREE)
+    (void)didstop;
+#else
+    if (!didstop) {
+      // Loop won’t block for I/O after this.
+      uv_stop(&loop->uv);
+      // XXX: Close all (lua/luv!) handles. But loop_walk_cb() does not call
+      // resource-specific close-callbacks, so this leaks memory...
+      uv_walk(&loop->uv, loop_walk_cb, NULL);
+      didstop = true;
+    }
+#endif
   }
   multiqueue_free(loop->fast_events);
   multiqueue_free(loop->thread_events);