Documentation on propagate exceptions feature

README.md

@@ -104,13 +104,25 @@ Future objects can have callbacks attached by using `Future.add_done_callback`.
 lets you specify default callbacks that will be applied to all new futures created by the executor:
 
 ```python
-    def some_callback(future):
-        # do something with future
-
-    executor.add_default_done_callback(some_callback)
+def some_callback(future):
+    # do something with future
 
-    # Callback will be added to the below task automatically
-    executor.submit(pow, 323, 1235)
+executor.add_default_done_callback(some_callback)
+
+# Callback will be added to the below task automatically
+executor.submit(pow, 323, 1235)
+```
+
+
+Propagate Exceptions
+--------------------
+
+Normally any exceptions thrown by background threads or processes will be swallowed unless explicitly
+checked for. To instead surface all exceptions thrown by background tasks, Flask-Executor can add
+a special default callback that raises any exceptions thrown by tasks submitted to the executor::
+
+```python
+app.config['EXECUTOR_PROPAGATE_EXCEPTIONS'] = True 
 ```
 
 

docs/index.rst

@@ -164,6 +164,16 @@ callbacks that will be applied to all new futures created by the executor::
     executor.submit(pow, 323, 1235)
 
 
+Propagate Exceptions
+--------------------
+
+Normally any exceptions thrown by background threads or processes will be swallowed unless explicitly
+checked for. To instead surface all exceptions thrown by background tasks, Flask-Executor can add
+a special default callback that raises any exceptions thrown by tasks submitted to the executor::
+
+    app.config['EXECUTOR_PROPAGATE_EXCEPTIONS'] = True    
+
+
 Indices and tables
 ==================
 

tests/test_executor.py

@@ -27,6 +27,9 @@ def request_context_test_value(_=None):
 def g_context_test_value(_=None):
     return g.test_value
 
+def fail():
+    print(hello)
+
 
 def test_init(app):
     executor = Executor(app)
@@ -241,13 +244,11 @@ def callback(future):
         concurrent.futures.wait([future])
         assert hasattr(future, 'test')
 
-def test_propagate_exception_callback(default_app):
-    default_app.config['EXECUTOR_PROPAGATE_EXCEPTIONS'] = True
-    executor = Executor(default_app)
-    def fail():
-        print(hello)
+def test_propagate_exception_callback(app):
+    app.config['EXECUTOR_PROPAGATE_EXCEPTIONS'] = True
+    executor = Executor(app)
     with pytest.raises(NameError):
-        with default_app.test_request_context('/'):
+        with app.test_request_context('/'):
             future = executor.submit(fail)
             concurrent.futures.wait([future])
             assert propagate_exceptions_callback in future._done_callbacks