add py_reader doc

python/paddle/fluid/layers/io.py

@@ -563,6 +563,7 @@ def _py_reader(capacity,
 
     def start_provide_thread(func):
         def __provider_thread__():
+            try:
                 for tensors in func():
                     array = core.LoDTensorArray()
                     for item in tensors:
@@ -579,6 +580,9 @@ def _py_reader(capacity,
                     if reader.exited:
                         break
                 feed_queue.close()
+            except Exception as ex:
+                feed_queue.close()
+                raise ex
 
         reader.thread = threading.Thread(target=__provider_thread__)
         reader.thread.daemon = True
@@ -692,6 +696,11 @@ def py_reader(capacity,
         >>>             exe.run(fetch_list=[loss.name])
         >>>     except fluid.core.EOFException:
         >>>         reader.reset()
+        >>>
+        >>> ...
+        >>>
+        >>> fluid.io.save_inference_model(dirname='./model', feeded_var_names=[img, label],
+        >>>     target_vars=[loss], executor=fluid.Executor(fluid.CUDAPlace(0)))  
 
         2. When training and testing are both performed, two different
         :code:`py_reader` should be created with different names, e.g.:

python/paddle/fluid/reader.py

@@ -250,6 +250,7 @@ class PyReader(object):
 
     def _start(self):
         def __thread_main__():
+            try:
                 for tensors in self._tensor_reader():
                     array = core.LoDTensorArray()
                     for item in tensors:
@@ -264,6 +265,9 @@ class PyReader(object):
                         break
 
                 self._queue.close()
+            except Exception as ex:
+                self._queue.close()
+                raise ex
 
         self._thread = threading.Thread(target=__thread_main__)
         self._thread.daemon = True