fix Error of gpu version paddle when CUDA device is not set properly (#27819)

* fix gpu version paddle Error when have no CUDA device

* optimize format and add new unittest

* fix coverage problem

* fix unittest format

* change static mode to dygraph mode

* use subprocess in unittest

python/paddle/fluid/framework.py

@@ -284,7 +284,17 @@ def _current_expected_place():
     global _global_expected_place_
     if _global_expected_place_ is None:
         if core.is_compiled_with_cuda():
-            _global_expected_place_ = core.CUDAPlace(0)
+            try:
+                device_count = core.get_cuda_device_count()
+            except Exception as e:
+                device_count = 0
+            if device_count > 0:
+                _global_expected_place_ = core.CUDAPlace(0)
+            else:
+                warnings.warn(
+                    "You are using GPU version Paddle, but your CUDA device is not set properly. CPU device will be used by default."
+                )
+                _global_expected_place_ = core.CPUPlace()
         else:
             _global_expected_place_ = core.CPUPlace()
 

python/paddle/fluid/tests/unittests/test_gpu_package_without_gpu_device.py

@@ -0,0 +1,57 @@
+#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import os
+import sys
+import subprocess
+import unittest
+import paddle
+import paddle.fluid as fluid
+from paddle.fluid import core
+
+
+class TestGPUPackagePaddle(unittest.TestCase):
+    def test_import_paddle(self):
+        if core.is_compiled_with_cuda():
+            os.environ['CUDA_VISIBLE_DEVICES'] = ''
+            test_file = 'test_no_gpu_run_rand.py'
+            with open(test_file, 'w') as wb:
+                cmd_test = """
+import paddle
+x = paddle.rand([3,4])
+assert x.place.is_gpu_place() is False, "There is no CUDA device, but Tensor's place is CUDAPlace"
+"""
+                wb.write(cmd_test)
+
+            _python = sys.executable
+
+            ps_cmd = '{} {}'.format(_python, test_file)
+            ps_proc = subprocess.Popen(
+                ps_cmd.strip().split(" "),
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE)
+            stdout, stderr = ps_proc.communicate()
+
+            assert 'CPU device will be used by default' in str(
+                stderr
+            ), "GPU version Paddle is installed. But CPU device can't be used when CUDA device is not set properly"
+            assert "Error" not in str(
+                stderr
+            ), "There is no CUDA device, but Tensor's place is CUDAPlace"
+
+
+if __name__ == '__main__':
+    unittest.main()