!4930 Fix CI cifar hang issue

Merge pull request !4930 from xiefangqi/fix_cifar_nofile_issue

mindspore/ccsrc/minddata/dataset/engine/datasetops/source/cifar_op.cc

@@ -336,6 +336,9 @@ Status CifarOp::GetCifarFiles() {
     std::string err_msg = "Unable to open directory " + dataset_directory.toString();
     RETURN_STATUS_UNEXPECTED(err_msg);
   }
+  if (cifar_files_.size() == 0) {
+    RETURN_STATUS_UNEXPECTED("No .bin files found under " + folder_path_);
+  }
   std::sort(cifar_files_.begin(), cifar_files_.end());
   return Status::OK();
 }

tests/ut/python/dataset/test_datasets_cifarop.py

@@ -24,6 +24,7 @@ from mindspore import log as logger
 
 DATA_DIR_10 = "../data/dataset/testCifar10Data"
 DATA_DIR_100 = "../data/dataset/testCifar100Data"
+NO_BIN_DIR = "../data/dataset/testMnistData"
 
 
 def load_cifar(path, kind="cifar10"):
@@ -208,6 +209,12 @@ def test_cifar10_exception():
     with pytest.raises(ValueError, match=error_msg_6):
         ds.Cifar10Dataset(DATA_DIR_10, shuffle=False, num_parallel_workers=88)
 
+    error_msg_7 = "No .bin files found"
+    with pytest.raises(RuntimeError, match=error_msg_7):
+        ds1 = ds.Cifar10Dataset(NO_BIN_DIR)
+        for _ in ds1.__iter__():
+            pass
+
 
 def test_cifar10_visualize(plot=False):
     """
@@ -352,6 +359,12 @@ def test_cifar100_exception():
     with pytest.raises(ValueError, match=error_msg_6):
         ds.Cifar100Dataset(DATA_DIR_100, shuffle=False, num_parallel_workers=88)
 
+    error_msg_7 = "No .bin files found"
+    with pytest.raises(RuntimeError, match=error_msg_7):
+        ds1 = ds.Cifar100Dataset(NO_BIN_DIR)
+        for _ in ds1.__iter__():
+            pass
+
 
 def test_cifar100_visualize(plot=False):
     """