Move in-flight callback check up

Fixes #3203 We entered a live lock race between the promotion callback and pollers, which was only resolved when the background executor got lucky enough to pick up the async work.
grpc · dgquintas · Sep 23, 2015 · Sep 9, 2015 · Sep 10, 2015 · Sep 11, 2015
commit 787fb130561bec4a8178720158d93ce01c031c8a
diff --git a/src/core/iomgr/pollset_posix.c b/src/core/iomgr/pollset_posix.c
@@ -187,6 +187,12 @@ void grpc_pollset_work(grpc_pollset *pollset, grpc_pollset_worker *worker,
   if (pollset->shutting_down) {
     goto done;
   }
+  if (pollset->in_flight_cbs) {
+    /* Give do_promote priority so we don't starve it out */
+    gpr_mu_unlock(&pollset->mu);
+    gpr_mu_lock(&pollset->mu);
+    goto done;
+  }
   if (!pollset->kicked_without_pollers) {
     push_front_worker(pollset, worker);
     added_worker = 1;
@@ -422,12 +428,6 @@ static void basic_pollset_maybe_work(grpc_pollset *pollset,
   int r;
   int nfds;
 
-  if (pollset->in_flight_cbs) {
-    /* Give do_promote priority so we don't starve it out */
-    gpr_mu_unlock(&pollset->mu);
-    gpr_mu_lock(&pollset->mu);
-    return;
-  }
   fd = pollset->data.ptr;
   if (fd && grpc_fd_is_orphaned(fd)) {
     GRPC_FD_UNREF(fd, "basicpoll");