Make pollset shutdown repeatedly kick until all threads have left poll.

src/core/iomgr/pollset_posix.c

@@ -184,9 +184,25 @@ int grpc_pollset_work(grpc_pollset *pollset, gpr_timespec deadline) {
   if (grpc_alarm_check(&pollset->mu, now, &deadline)) {
     return 1;
   }
+  if (pollset->shutting_down) {
+    return 1;
+  }
   gpr_tls_set(&g_current_thread_poller, (gpr_intptr)pollset);
   r = pollset->vtable->maybe_work(pollset, deadline, now, 1);
   gpr_tls_set(&g_current_thread_poller, 0);
+  if (pollset->shutting_down) {
+    if (pollset->counter > 0) {
+      grpc_pollset_kick(pollset);
+    } else if (pollset->in_flight_cbs == 0) {
+      gpr_mu_unlock(&pollset->mu);
+      pollset->shutdown_done_cb(pollset->shutdown_done_arg);
+      /* Continuing to access pollset here is safe -- it is the caller's
+       * responsibility to not destroy when it has outstanding calls to
+       * grpc_pollset_work.
+       * TODO(dklempner): Can we refactor the shutdown logic to avoid this? */
+      gpr_mu_lock(&pollset->mu);
+    }
+  }
   return r;
 }
 
@@ -194,13 +210,19 @@ void grpc_pollset_shutdown(grpc_pollset *pollset,
                            void (*shutdown_done)(void *arg),
                            void *shutdown_done_arg) {
   int in_flight_cbs;
+  int counter;
   gpr_mu_lock(&pollset->mu);
   pollset->shutting_down = 1;
   in_flight_cbs = pollset->in_flight_cbs;
+  counter = pollset->counter;
   pollset->shutdown_done_cb = shutdown_done;
   pollset->shutdown_done_arg = shutdown_done_arg;
+  if (counter > 0) {
+    grpc_pollset_kick(pollset);
+  }
   gpr_mu_unlock(&pollset->mu);
-  if (in_flight_cbs == 0) {
+
+  if (in_flight_cbs == 0 && counter == 0) {
     shutdown_done(shutdown_done_arg);
   }
 }
@@ -286,7 +308,7 @@ static void unary_poll_do_promote(void *args, int success) {
   pollset->in_flight_cbs--;
   if (pollset->shutting_down) {
     /* We don't care about this pollset anymore. */
-    if (pollset->in_flight_cbs == 0) {
+    if (pollset->in_flight_cbs == 0 && pollset->counter == 0) {
       do_shutdown_cb = 1;
     }
   } else if (grpc_fd_is_orphaned(fd)) {