Merge pull request #2779 from jtattermusch/properly_decrement_active_ports

Properly decrement active_ports on server shutdown on Win.

src/core/iomgr/tcp_server_windows.c

@@ -186,6 +186,17 @@ error:
   return -1;
 }
 
+static void decrement_active_ports_and_notify(server_port *sp) {
+  sp->shutting_down = 0;
+  sp->socket->read_info.outstanding = 0;
+  gpr_mu_lock(&sp->server->mu);
+  GPR_ASSERT(sp->server->active_ports > 0);
+  if (0 == --sp->server->active_ports) {
+    gpr_cv_broadcast(&sp->server->cv);
+  }
+  gpr_mu_unlock(&sp->server->mu);
+}
+
 /* start_accept will reference that for the IOCP notification request. */
 static void on_accept(void *arg, int from_iocp);
 
@@ -234,6 +245,15 @@ static void start_accept(server_port *port) {
   return;
 
 failure:
+  if (port->shutting_down) {
+    /* We are abandoning the listener port, take that into account to prevent
+       occasional hangs on shutdown. The hang happens when sp->shutting_down
+       change is not seen by on_accept and we proceed to trying new accept,
+       but we fail there because the listening port has been closed in the
+       meantime. */
+    decrement_active_ports_and_notify(port);
+    return;
+  }
   utf8_message = gpr_format_message(WSAGetLastError());
   gpr_log(GPR_ERROR, message, utf8_message);
   gpr_free(utf8_message);
@@ -277,14 +297,7 @@ static void on_accept(void *arg, int from_iocp) {
     if (sp->shutting_down) {
       /* During the shutdown case, we ARE expecting an error. So that's well,
          and we can wake up the shutdown thread. */
-      sp->shutting_down = 0;
-      sp->socket->read_info.outstanding = 0;
-      gpr_mu_lock(&sp->server->mu);
-      GPR_ASSERT(sp->server->active_ports > 0);
-      if (0 == --sp->server->active_ports) {
-        gpr_cv_broadcast(&sp->server->cv);
-      }
-      gpr_mu_unlock(&sp->server->mu);
+      decrement_active_ports_and_notify(sp);
       return;
     } else {
       char *utf8_message = gpr_format_message(WSAGetLastError());