refactor: make code more readable by extracting a function

dipu/torch_dipu/csrc_dipu/vendor/ascend/deviceimpl.cpp

@@ -17,9 +17,24 @@ namespace devapis {
 //  Device class related
 // =====================
 using AscendDeviceId = int32_t;
+
+namespace {
+
 constexpr AscendDeviceId kDeviceIdUnset = -1;
 constexpr AscendDeviceId kDeviceIdDefault = 0;
-static thread_local auto g_current_thread_device_id = kDeviceIdUnset;
+thread_local auto g_current_thread_device_id = kDeviceIdUnset;
+
+// atomically set global device id if it is unset
+// and anyway return the global device id
+AscendDeviceId setOrGetGlobalDeviceId(AscendDeviceId device_id_if_unset) {
+  static std::atomic global_device_id = kDeviceIdUnset;
+  auto expectedUnset = kDeviceIdUnset;
+  std::atomic_compare_exchange_strong(&global_device_id, &expectedUnset,
+                                      device_id_if_unset);
+  return global_device_id.load();
+}
+
+}  // namespace
 
 void initializeVendor() {
   DIPU_CALLACLRT(aclInit(nullptr));
@@ -46,10 +61,7 @@ void setDevice(deviceId_t device_id) {
   }
   auto ascend_device_id = static_cast<AscendDeviceId>(device_id);
   if (g_current_thread_device_id == kDeviceIdUnset) {
-    static std::atomic g_global_device_id = kDeviceIdUnset;
-    std::atomic_compare_exchange_strong(
-        &g_global_device_id, &g_current_thread_device_id, ascend_device_id);
-    g_current_thread_device_id = g_global_device_id.load();
+    g_current_thread_device_id = setOrGetGlobalDeviceId(ascend_device_id);
   }
   if (ascend_device_id != g_current_thread_device_id) {
     DIPU_LOGW(