Fix tsan reported error

test/core/client_config/set_initial_connect_string_test.c

@@ -57,7 +57,7 @@ struct rpc_state {
   gpr_slice_buffer incoming_buffer;
   gpr_slice_buffer temp_incoming_buffer;
   grpc_endpoint *tcp;
-  int done;
+  gpr_atm done_atm;
 };
 
 static const char *magic_connect_string = "magic initial string";
@@ -70,7 +70,7 @@ static void handle_read(grpc_exec_ctx *exec_ctx, void *arg, bool success) {
   gpr_slice_buffer_move_into(&state.temp_incoming_buffer,
                              &state.incoming_buffer);
   if (state.incoming_buffer.length > strlen(magic_connect_string)) {
-    state.done = 1;
+    gpr_atm_rel_store(&state.done_atm, 1);
     grpc_endpoint_shutdown(exec_ctx, state.tcp);
     grpc_endpoint_destroy(exec_ctx, state.tcp);
   } else {
@@ -117,7 +117,7 @@ static gpr_timespec n_sec_deadline(int seconds) {
 }
 
 static void start_rpc(int use_creds, int target_port) {
-  state.done = 0;
+  gpr_atm_rel_store(&state.done_atm, 0);
   state.cq = grpc_completion_queue_create(NULL);
   if (use_creds) {
     state.creds = grpc_fake_transport_security_credentials_create();
@@ -166,7 +166,7 @@ typedef struct {
 static void actually_poll_server(void *arg) {
   poll_args *pa = arg;
   gpr_timespec deadline = n_sec_deadline(10);
-  while (state.done == 0 &&
+  while (gpr_atm_acq_load(&state.done_atm) == 0 &&
          gpr_time_cmp(gpr_now(GPR_CLOCK_REALTIME), deadline) < 0) {
     test_tcp_server_poll(pa->server, 1);
   }