Fallback method support

src/pybreaker.py

@@ -50,7 +50,8 @@ class CircuitBreaker(object):
     """
 
     def __init__(self, fail_max=5, reset_timeout=60, exclude=None,
-                 listeners=None, state_storage=None, name=None):
+                 listeners=None, state_storage=None, name=None,
+                 fallback_method=None):
         """
         Creates a new circuit breaker with the given parameters.
         """
@@ -64,6 +65,22 @@ def __init__(self, fail_max=5, reset_timeout=60, exclude=None,
         self._excluded_exceptions = list(exclude or [])
         self._listeners = list(listeners or [])
         self._name = name
+        self._fallback_method = fallback_method
+
+    @property
+    def fallback_method(self):
+        """
+        Return the current fallback method
+        """
+        return self._fallback_method
+
+    @fallback_method.setter
+    def fallback_method(self, func):
+        """
+        Sets the fallback function that will be called when the circuit is open
+        :param func:
+        """
+        self._fallback_method = func
 
     @property
     def fail_counter(self):
@@ -205,7 +222,15 @@ def call(self, func, *args, **kwargs):
         implemented by the current state of this circuit breaker.
         """
         with self._lock:
-            return self.state.call(func, *args, **kwargs)
+            try:
+                result = self.state.call(func, *args, **kwargs)
+            except CircuitBreakerError as e:
+                if self.fallback_method:
+                    result = self.fallback_method(*args, **kwargs)
+                else:
+                    raise e
+
+            return result
 
     def call_async(self, func, *args, **kwargs):
         """
@@ -219,7 +244,21 @@ def wrapped():
             with self._lock:
                 ret = yield self.state.call_async(func, *args, **kwargs)
                 raise gen.Return(ret)
-        return wrapped()
+
+        @gen.coroutine
+        def fallback_wrapped():
+            with self._lock:
+                ret = yield self.fallback_method(*args, **kwargs)
+                raise gen.Return(ret)
+        try:
+            result = wrapped()
+        except CircuitBreakerError as e:
+            if self.fallback_method:
+                result = fallback_wrapped()
+            else:
+                raise e
+
+        return result
 
     def open(self):
         """
@@ -254,6 +293,7 @@ def __call__(self, *call_args, **call_kwargs):
         which will will call `func` as a Tornado co-routine.
         """
         call_async = call_kwargs.pop('__pybreaker_call_async', False)
+        self.fallback_method = call_kwargs.pop('__pybreaker_fallback', None)
 
         if call_async and not HAS_TORNADO_SUPPORT:
             raise ImportError('No module named tornado')