fix race in server shutdown

src/core/iomgr/tcp_server_windows.c

@@ -79,6 +79,8 @@ struct grpc_tcp_server {
 
   /* active port count: how many ports are actually still listening */
   int active_ports;
+  /* number of iomgr callbacks that have been explicitly scheduled during shutdown */
+  int iomgr_callbacks_pending;
 
   /* all listening ports */
   server_port *ports;
@@ -93,6 +95,7 @@ grpc_tcp_server *grpc_tcp_server_create(void) {
   gpr_mu_init(&s->mu);
   gpr_cv_init(&s->cv);
   s->active_ports = 0;
+  s->iomgr_callbacks_pending = 0;
   s->cb = NULL;
   s->cb_arg = NULL;
   s->ports = gpr_malloc(sizeof(server_port) * INIT_PORT_CAP);
@@ -112,10 +115,10 @@ void grpc_tcp_server_destroy(grpc_tcp_server *s,
   for (i = 0; i < s->nports; i++) {
     server_port *sp = &s->ports[i];
     sp->shutting_down = 1;
-    grpc_winsocket_shutdown(sp->socket);
+    s->iomgr_callbacks_pending += grpc_winsocket_shutdown(sp->socket);
   }
   /* This happens asynchronously. Wait while that happens. */
-  while (s->active_ports) {
+  while (s->active_ports || s->iomgr_callbacks_pending) {
     gpr_cv_wait(&s->cv, &s->mu, gpr_inf_future(GPR_CLOCK_REALTIME));
   }
   gpr_mu_unlock(&s->mu);
@@ -254,8 +257,16 @@ static void on_accept(void *arg, int from_iocp) {
 
   /* The general mechanism for shutting down is to queue abortion calls. While
      this is necessary in the read/write case, it's useless for the accept
-     case. Let's do nothing. */
-  if (!from_iocp) return;
+     case. We only need to adjust the pending callback count */
+  if (!from_iocp) {
+    gpr_mu_lock(&sp->server->mu);
+    GPR_ASSERT(sp->server->iomgr_callbacks_pending > 0);
+    if (0 == --sp->server->iomgr_callbacks_pending) {
+      gpr_cv_broadcast(&sp->server->cv);
+    }
+    gpr_mu_unlock(&sp->server->mu);
+    return;
+  }
 
   /* The IOCP notified us of a completed operation. Let's grab the results,
       and act accordingly. */
@@ -264,11 +275,12 @@ static void on_accept(void *arg, int from_iocp) {
                                             &transfered_bytes, FALSE, &flags);
   if (!wsa_success) {
     if (sp->shutting_down) {
-      /* During the shutdown case, we ARE expecting an error. So that's swell,
+      /* 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);
       }