--- /dev/null
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE UnboxedTuples #-}
+{-# LANGUAGE ViewPatterns #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module : Control.Retry
+-- Copyright : Ozgun Ataman <ozgun.ataman@soostone.com>
+-- License : BSD3
+--
+-- Maintainer : Ozgun Ataman
+-- Stability : provisional
+--
+-- This module exposes combinators that can wrap arbitrary monadic
+-- actions. They run the action and potentially retry running it with
+-- some configurable delay for a configurable number of times.
+--
+-- The express purpose of this library is to make it easier to work
+-- with IO and especially network IO actions that often experience
+-- temporary failure that warrant retrying of the original action. For
+-- example, a database query may time out for a while, in which case
+-- we should delay a bit and retry the query.
+----------------------------------------------------------------------------
+
+
+module Control.Retry
+ (
+ -- * Types and Operations
+ RetryPolicyM (..)
+ , RetryPolicy
+ , retryPolicy
+ , retryPolicyDefault
+ , natTransformRetryPolicy
+ , RetryAction (..)
+ , toRetryAction
+ , RetryStatus (..)
+ , defaultRetryStatus
+ , applyPolicy
+ , applyAndDelay
+
+
+ -- ** Lenses for 'RetryStatus'
+ , rsIterNumberL
+ , rsCumulativeDelayL
+ , rsPreviousDelayL
+
+ -- * Applying Retry Policies
+ , retrying
+ , retryingDynamic
+ , recovering
+ , recoveringDynamic
+ , stepping
+ , recoverAll
+ , skipAsyncExceptions
+ , logRetries
+ , defaultLogMsg
+
+ -- * Retry Policies
+ , constantDelay
+ , exponentialBackoff
+ , fullJitterBackoff
+ , fibonacciBackoff
+ , limitRetries
+
+ -- * Policy Transformers
+ , limitRetriesByDelay
+ , limitRetriesByCumulativeDelay
+ , capDelay
+
+ -- * Development Helpers
+ , simulatePolicy
+ , simulatePolicyPP
+ ) where
+
+-------------------------------------------------------------------------------
+import Control.Applicative
+import Control.Concurrent
+#if MIN_VERSION_base(4, 7, 0)
+import Control.Exception (AsyncException, SomeAsyncException)
+#else
+import Control.Exception (AsyncException)
+#endif
+import Control.Monad
+import Control.Monad.Catch
+import Control.Monad.IO.Class
+import Control.Monad.Trans.Class
+import Control.Monad.Trans.Maybe
+import Control.Monad.Trans.State
+import Data.List (foldl')
+import Data.Maybe
+import GHC.Generics
+import GHC.Prim
+import GHC.Types (Int(I#))
+import System.Random
+# if MIN_VERSION_base(4, 9, 0)
+import Data.Semigroup
+# else
+import Data.Monoid
+# endif
+import Prelude
+-------------------------------------------------------------------------------
+
+
+-------------------------------------------------------------------------------
+-- | A 'RetryPolicyM' is a function that takes an 'RetryStatus' and
+-- possibly returns a delay in microseconds. Iteration numbers start
+-- at zero and increase by one on each retry. A *Nothing* return value from
+-- the function implies we have reached the retry limit.
+--
+-- Please note that 'RetryPolicyM' is a 'Monoid'. You can collapse
+-- multiple strategies into one using 'mappend' or '<>'. The semantics
+-- of this combination are as follows:
+--
+-- 1. If either policy returns 'Nothing', the combined policy returns
+-- 'Nothing'. This can be used to @inhibit@ after a number of retries,
+-- for example.
+--
+-- 2. If both policies return a delay, the larger delay will be used.
+-- This is quite natural when combining multiple policies to achieve a
+-- certain effect.
+--
+-- Example:
+--
+-- One can easily define an exponential backoff policy with a limited
+-- number of retries:
+--
+-- >> limitedBackoff = exponentialBackoff 50 <> limitRetries 5
+--
+-- Naturally, 'mempty' will retry immediately (delay 0) for an
+-- unlimited number of retries, forming the identity for the 'Monoid'.
+--
+-- The default retry policy 'retryPolicyDefault' implements a constant 50ms delay, up to 5 times:
+--
+-- >> retryPolicyDefault = constantDelay 50000 <> limitRetries 5
+--
+-- For anything more complex, just define your own 'RetryPolicyM':
+--
+-- >> myPolicy = retryPolicy $ \ rs -> if rsIterNumber n > 10 then Just 1000 else Just 10000
+--
+-- Since 0.7.
+newtype RetryPolicyM m = RetryPolicyM { getRetryPolicyM :: RetryStatus -> m (Maybe Int) }
+
+
+-- | Simplified 'RetryPolicyM' without any use of the monadic context in
+-- determining policy. Mostly maintains backwards compatitibility with
+-- type signatures pre-0.7.
+type RetryPolicy = forall m . Monad m => RetryPolicyM m
+
+-- | Default retry policy
+retryPolicyDefault :: RetryPolicy
+retryPolicyDefault = constantDelay 50000 <> limitRetries 5
+
+
+-- Base 4.9.0 adds a Data.Semigroup module. This has fewer
+-- dependencies than the semigroups package, so we're using base's
+-- only if its available.
+# if MIN_VERSION_base(4, 9, 0)
+instance Monad m => Semigroup (RetryPolicyM m) where
+ (RetryPolicyM a) <> (RetryPolicyM b) = RetryPolicyM $ \ n -> runMaybeT $ do
+ a' <- MaybeT $ a n
+ b' <- MaybeT $ b n
+ return $! max a' b'
+
+
+instance Monad m => Monoid (RetryPolicyM m) where
+ mempty = retryPolicy $ const (Just 0)
+ mappend = (<>)
+# else
+instance Monad m => Monoid (RetryPolicyM m) where
+ mempty = retryPolicy $ const (Just 0)
+ (RetryPolicyM a) `mappend` (RetryPolicyM b) = RetryPolicyM $ \ n -> runMaybeT $ do
+ a' <- MaybeT $ a n
+ b' <- MaybeT $ b n
+ return $! max a' b'
+#endif
+
+
+-------------------------------------------------------------------------------
+-- | Applies a natural transformation to a policy to run a RetryPolicy
+-- meant for the monad @m@ in the monad @n@ provided a transformation
+-- from @m@ to @n@ is available. A common case is if you have a pure
+-- policy, @RetryPolicyM Identity@ and want to use it to govern an
+-- @IO@ computation you could write:
+--
+-- @
+-- purePolicyInIO :: RetryPolicyM Identity -> RetryPolicyM IO
+-- purePolicyInIO = natTransformRetryPolicy (pure . runIdentity)
+-- @
+natTransformRetryPolicy :: (forall a. m a -> n a) -> RetryPolicyM m -> RetryPolicyM n
+natTransformRetryPolicy f (RetryPolicyM p) = RetryPolicyM $ \stat -> f (p stat)
+
+
+-- | Modify the delay of a RetryPolicy.
+-- Does not change whether or not a retry is performed.
+modifyRetryPolicyDelay :: Functor m => (Int -> Int) -> RetryPolicyM m -> RetryPolicyM m
+modifyRetryPolicyDelay f (RetryPolicyM p) = RetryPolicyM $ \stat -> fmap f <$> p stat
+
+
+-------------------------------------------------------------------------------
+-- | How to handle a failed action.
+data RetryAction
+ = DontRetry
+ -- ^ Don't retry (regardless of what the 'RetryPolicy' says).
+ | ConsultPolicy
+ -- ^ Retry if the 'RetryPolicy' says so, with the delay specified by the policy.
+ | ConsultPolicyOverrideDelay Int
+ -- ^ Retry if the 'RetryPolicy' says so, but override the policy's delay (number of microseconds).
+ deriving (Read, Show, Eq, Generic)
+
+
+-- | Convert a boolean answer to the question "Should we retry?" into
+-- a 'RetryAction'.
+toRetryAction :: Bool -> RetryAction
+toRetryAction False = DontRetry
+toRetryAction True = ConsultPolicy
+
+-------------------------------------------------------------------------------
+-- | Datatype with stats about retries made thus far. The constructor
+-- is deliberately not exported to make additional fields easier to
+-- add in a backward-compatible manner. To read or modify fields in
+-- RetryStatus, use the accessors or lenses below. Note that if you
+-- don't want to use lenses, the exported field names can be used for
+-- updates:
+--
+-- >> retryStatus { rsIterNumber = newIterNumber }
+-- >> retryStatus & rsIterNumberL .~ newIterNumber
+data RetryStatus = RetryStatus
+ { rsIterNumber :: !Int -- ^ Iteration number, where 0 is the first try
+ , rsCumulativeDelay :: !Int -- ^ Delay incurred so far from retries in microseconds
+ , rsPreviousDelay :: !(Maybe Int) -- ^ Latest attempt's delay. Will always be Nothing on first run.
+ } deriving (Read, Show, Eq, Generic)
+
+
+-------------------------------------------------------------------------------
+-- | Initial, default retry status. Exported mostly to allow user code
+-- to test their handlers and retry policies. Use fields or lenses to update.
+defaultRetryStatus :: RetryStatus
+defaultRetryStatus = RetryStatus 0 0 Nothing
+
+-------------------------------------------------------------------------------
+rsIterNumberL :: Lens' RetryStatus Int
+rsIterNumberL = lens rsIterNumber (\rs x -> rs { rsIterNumber = x })
+{-# INLINE rsIterNumberL #-}
+
+
+-------------------------------------------------------------------------------
+rsCumulativeDelayL :: Lens' RetryStatus Int
+rsCumulativeDelayL = lens rsCumulativeDelay (\rs x -> rs { rsCumulativeDelay = x })
+{-# INLINE rsCumulativeDelayL #-}
+
+
+-------------------------------------------------------------------------------
+rsPreviousDelayL :: Lens' RetryStatus (Maybe Int)
+rsPreviousDelayL = lens rsPreviousDelay (\rs x -> rs { rsPreviousDelay = x })
+{-# INLINE rsPreviousDelayL #-}
+
+
+
+-------------------------------------------------------------------------------
+-- | Apply policy on status to see what the decision would be.
+-- 'Nothing' implies no retry, 'Just' returns updated status.
+applyPolicy
+ :: Monad m
+ => RetryPolicyM m
+ -> RetryStatus
+ -> m (Maybe RetryStatus)
+applyPolicy (RetryPolicyM policy) s = do
+ res <- policy s
+ case res of
+ Just delay -> return $! Just $! RetryStatus
+ { rsIterNumber = rsIterNumber s + 1
+ , rsCumulativeDelay = rsCumulativeDelay s `boundedPlus` delay
+ , rsPreviousDelay = Just delay }
+ Nothing -> return Nothing
+
+
+-------------------------------------------------------------------------------
+-- | Apply policy and delay by its amount if it results in a retry.
+-- Return updated status.
+applyAndDelay
+ :: MonadIO m
+ => RetryPolicyM m
+ -> RetryStatus
+ -> m (Maybe RetryStatus)
+applyAndDelay policy s = do
+ chk <- applyPolicy policy s
+ case chk of
+ Just rs -> do
+ case (rsPreviousDelay rs) of
+ Nothing -> return ()
+ Just delay -> liftIO $ threadDelay delay
+ return (Just rs)
+ Nothing -> return Nothing
+
+
+
+-------------------------------------------------------------------------------
+-- | Helper for making simplified policies that don't use the monadic
+-- context.
+retryPolicy :: (RetryStatus -> Maybe Int) -> RetryPolicy
+retryPolicy f = RetryPolicyM $ \ s -> return (f s)
+
+
+-------------------------------------------------------------------------------
+-- | Retry immediately, but only up to @n@ times.
+limitRetries
+ :: Int
+ -- ^ Maximum number of retries.
+ -> RetryPolicy
+limitRetries i = retryPolicy $ \ RetryStatus { rsIterNumber = n} -> if n >= i then Nothing else (Just 0)
+
+
+-------------------------------------------------------------------------------
+-- | Add an upperbound to a policy such that once the given time-delay
+-- amount *per try* has been reached or exceeded, the policy will stop
+-- retrying and fail. If you need to stop retrying once *cumulative*
+-- delay reaches a time-delay amount, use
+-- 'limitRetriesByCumulativeDelay'
+limitRetriesByDelay
+ :: Monad m
+ => Int
+ -- ^ Time-delay limit in microseconds.
+ -> RetryPolicyM m
+ -> RetryPolicyM m
+limitRetriesByDelay i p = RetryPolicyM $ \ n ->
+ (>>= limit) `liftM` getRetryPolicyM p n
+ where
+ limit delay = if delay >= i then Nothing else Just delay
+
+
+-------------------------------------------------------------------------------
+-- | Add an upperbound to a policy such that once the cumulative delay
+-- over all retries has reached or exceeded the given limit, the
+-- policy will stop retrying and fail.
+limitRetriesByCumulativeDelay
+ :: Monad m
+ => Int
+ -- ^ Time-delay limit in microseconds.
+ -> RetryPolicyM m
+ -> RetryPolicyM m
+limitRetriesByCumulativeDelay cumulativeLimit p = RetryPolicyM $ \ stat ->
+ (>>= limit stat) `liftM` getRetryPolicyM p stat
+ where
+ limit status curDelay
+ | rsCumulativeDelay status `boundedPlus` curDelay > cumulativeLimit = Nothing
+ | otherwise = Just curDelay
+
+
+-------------------------------------------------------------------------------
+-- | Implement a constant delay with unlimited retries.
+constantDelay
+ :: Int
+ -- ^ Base delay in microseconds
+ -> RetryPolicy
+constantDelay delay = retryPolicy (const (Just delay))
+
+
+-------------------------------------------------------------------------------
+-- | Grow delay exponentially each iteration. Each delay will
+-- increase by a factor of two.
+exponentialBackoff
+ :: Int
+ -- ^ Base delay in microseconds
+ -> RetryPolicy
+exponentialBackoff base = retryPolicy $ \ RetryStatus { rsIterNumber = n } ->
+ Just $! base `boundedMult` boundedPow 2 n
+
+-------------------------------------------------------------------------------
+-- | FullJitter exponential backoff as explained in AWS Architecture
+-- Blog article.
+--
+-- @http:\/\/www.awsarchitectureblog.com\/2015\/03\/backoff.html@
+--
+-- temp = min(cap, base * 2 ** attempt)
+--
+-- sleep = temp \/ 2 + random_between(0, temp \/ 2)
+fullJitterBackoff
+ :: MonadIO m
+ => Int
+ -- ^ Base delay in microseconds
+ -> RetryPolicyM m
+fullJitterBackoff base = RetryPolicyM $ \ RetryStatus { rsIterNumber = n } -> do
+ let d = (base `boundedMult` boundedPow 2 n) `div` 2
+ rand <- liftIO $ randomRIO (0, d)
+ return $! Just $! d `boundedPlus` rand
+
+
+-------------------------------------------------------------------------------
+-- | Implement Fibonacci backoff.
+fibonacciBackoff
+ :: Int
+ -- ^ Base delay in microseconds
+ -> RetryPolicy
+fibonacciBackoff base = retryPolicy $ \RetryStatus { rsIterNumber = n } ->
+ Just $ fib (n + 1) (0, base)
+ where
+ fib 0 (a, _) = a
+ fib !m (!a, !b) = fib (m-1) (b, a `boundedPlus` b)
+
+
+-------------------------------------------------------------------------------
+-- | Set a time-upperbound for any delays that may be directed by the
+-- given policy. This function does not terminate the retrying. The policy
+-- `capDelay maxDelay (exponentialBackoff n)` will never stop retrying. It
+-- will reach a state where it retries forever with a delay of `maxDelay`
+-- between each one. To get termination you need to use one of the
+-- 'limitRetries' function variants.
+capDelay
+ :: Monad m
+ => Int
+ -- ^ A maximum delay in microseconds
+ -> RetryPolicyM m
+ -> RetryPolicyM m
+capDelay limit p = RetryPolicyM $ \ n ->
+ (fmap (min limit)) `liftM` (getRetryPolicyM p) n
+
+
+-------------------------------------------------------------------------------
+-- | Retry combinator for actions that don't raise exceptions, but
+-- signal in their type the outcome has failed. Examples are the
+-- 'Maybe', 'Either' and 'EitherT' monads.
+--
+-- Let's write a function that always fails and watch this combinator
+-- retry it 5 additional times following the initial run:
+--
+-- >>> import Data.Maybe
+-- >>> let f _ = putStrLn "Running action" >> return Nothing
+-- >>> retrying retryPolicyDefault (const $ return . isNothing) f
+-- Running action
+-- Running action
+-- Running action
+-- Running action
+-- Running action
+-- Running action
+-- Nothing
+--
+-- Note how the latest failing result is returned after all retries
+-- have been exhausted.
+retrying :: MonadIO m
+ => RetryPolicyM m
+ -> (RetryStatus -> b -> m Bool)
+ -- ^ An action to check whether the result should be retried.
+ -- If True, we delay and retry the operation.
+ -> (RetryStatus -> m b)
+ -- ^ Action to run
+ -> m b
+retrying policy chk f =
+ retryingDynamic policy (\rs -> fmap toRetryAction . chk rs) f
+
+
+-------------------------------------------------------------------------------
+-- | Same as 'retrying', but with the ability to override
+-- the delay of the retry policy based on information
+-- obtained after initiation.
+--
+-- For example, if the action to run is a HTTP request that
+-- turns out to fail with a status code 429 ("too many requests"),
+-- the response may contain a "Retry-After" HTTP header which
+-- specifies the number of seconds
+-- the client should wait until performing the next request.
+-- This function allows overriding the delay calculated by the given
+-- retry policy with the delay extracted from this header value.
+--
+-- In other words, given an arbitrary 'RetryPolicyM' @rp@, the
+-- following invocation will always delay by 1000 microseconds:
+--
+-- > retryingDynamic rp (\_ _ -> return $ ConsultPolicyOverrideDelay 1000) f
+--
+-- Note that a 'RetryPolicy's decision to /not/ perform a retry
+-- cannot be overridden. Ie. /when/ to /stop/ retrying is always decided
+-- by the retry policy, regardless of the returned 'RetryAction' value.
+retryingDynamic
+ :: MonadIO m
+ => RetryPolicyM m
+ -> (RetryStatus -> b -> m RetryAction)
+ -- ^ An action to check whether the result should be retried.
+ -- The returned 'RetryAction' determines how/if a retry is performed.
+ -- See documentation on 'RetryAction'.
+ -> (RetryStatus -> m b)
+ -- ^ Action to run
+ -> m b
+retryingDynamic policy chk f = go defaultRetryStatus
+ where
+ go s = do
+ res <- f s
+ let consultPolicy policy' = do
+ rs <- applyAndDelay policy' s
+ case rs of
+ Nothing -> return res
+ Just rs' -> go $! rs'
+ chk' <- chk s res
+ case chk' of
+ DontRetry -> return res
+ ConsultPolicy -> consultPolicy policy
+ ConsultPolicyOverrideDelay delay ->
+ consultPolicy $ modifyRetryPolicyDelay (const delay) policy
+
+
+-------------------------------------------------------------------------------
+-- | Retry ALL exceptions that may be raised. To be used with caution;
+-- this matches the exception on 'SomeException'. Note that this
+-- handler explicitly does not handle 'AsyncException' nor
+-- 'SomeAsyncException' (for versions of base >= 4.7). It is not a
+-- good idea to catch async exceptions as it can result in hanging
+-- threads and programs. Note that if you just throw an exception to
+-- this thread that does not descend from SomeException, recoverAll
+-- will not catch it.
+--
+-- See how the action below is run once and retried 5 more times
+-- before finally failing for good:
+--
+-- >>> let f _ = putStrLn "Running action" >> error "this is an error"
+-- >>> recoverAll retryPolicyDefault f
+-- Running action
+-- Running action
+-- Running action
+-- Running action
+-- Running action
+-- Running action
+-- *** Exception: this is an error
+recoverAll
+#if MIN_VERSION_exceptions(0, 6, 0)
+ :: (MonadIO m, MonadMask m)
+#else
+ :: (MonadIO m, MonadCatch m)
+#endif
+ => RetryPolicyM m
+ -> (RetryStatus -> m a)
+ -> m a
+recoverAll set f = recovering set handlers f
+ where
+ handlers = skipAsyncExceptions ++ [h]
+ h _ = Handler $ \ (_ :: SomeException) -> return True
+
+
+-------------------------------------------------------------------------------
+-- | List of pre-made handlers that will skip retries on
+-- 'AsyncException' and 'SomeAsyncException'. Append your handlers to
+-- this list as a convenient way to make sure you're not catching
+-- async exceptions like user interrupt.
+skipAsyncExceptions
+ :: ( MonadIO m
+ )
+ => [RetryStatus -> Handler m Bool]
+skipAsyncExceptions = handlers
+ where
+ asyncH _ = Handler $ \ (_ :: AsyncException) -> return False
+#if MIN_VERSION_base(4, 7, 0)
+ someAsyncH _ = Handler $ \(_ :: SomeAsyncException) -> return False
+ handlers = [asyncH, someAsyncH]
+#else
+ handlers = [asyncH]
+#endif
+
+
+-------------------------------------------------------------------------------
+-- | Run an action and recover from a raised exception by potentially
+-- retrying the action a number of times. Note that if you're going to
+-- use a handler for 'SomeException', you should add explicit cases
+-- *earlier* in the list of handlers to reject 'AsyncException' and
+-- 'SomeAsyncException', as catching these can cause thread and
+-- program hangs. 'recoverAll' already does this for you so if you
+-- just plan on catching 'SomeException', you may as well ues
+-- 'recoverAll'
+recovering
+#if MIN_VERSION_exceptions(0, 6, 0)
+ :: (MonadIO m, MonadMask m)
+#else
+ :: (MonadIO m, MonadCatch m)
+#endif
+ => RetryPolicyM m
+ -- ^ Just use 'retryPolicyDefault' for default settings
+ -> [(RetryStatus -> Handler m Bool)]
+ -- ^ Should a given exception be retried? Action will be
+ -- retried if this returns True *and* the policy allows it.
+ -- This action will be consulted first even if the policy
+ -- later blocks it.
+ -> (RetryStatus -> m a)
+ -- ^ Action to perform
+ -> m a
+recovering policy hs f =
+ recoveringDynamic policy hs' f
+ where
+ hs' = map (fmap toRetryAction .) hs
+
+-- | The difference between this and 'recovering' is the same as
+-- the difference between 'retryingDynamic' and 'retrying'.
+recoveringDynamic
+#if MIN_VERSION_exceptions(0, 6, 0)
+ :: (MonadIO m, MonadMask m)
+#else
+ :: (MonadIO m, MonadCatch m)
+#endif
+ => RetryPolicyM m
+ -- ^ Just use 'retryPolicyDefault' for default settings
+ -> [(RetryStatus -> Handler m RetryAction)]
+ -- ^ Should a given exception be retried? Action will be
+ -- retried if this returns either 'ConsultPolicy' or
+ -- 'ConsultPolicyOverrideDelay' *and* the policy allows it.
+ -- This action will be consulted first even if the policy
+ -- later blocks it.
+ -> (RetryStatus -> m a)
+ -- ^ Action to perform
+ -> m a
+recoveringDynamic policy hs f = mask $ \restore -> go restore defaultRetryStatus
+ where
+ go restore = loop
+ where
+ loop s = do
+ r <- try $ restore (f s)
+ case r of
+ Right x -> return x
+ Left e -> recover (e :: SomeException) hs
+ where
+ recover e [] = throwM e
+ recover e ((($ s) -> Handler h) : hs')
+ | Just e' <- fromException e = do
+ let consultPolicy policy' = do
+ rs <- applyAndDelay policy' s
+ case rs of
+ Just rs' -> loop $! rs'
+ Nothing -> throwM e'
+ chk <- h e'
+ case chk of
+ DontRetry -> throwM e'
+ ConsultPolicy -> consultPolicy policy
+ ConsultPolicyOverrideDelay delay ->
+ consultPolicy $ modifyRetryPolicyDelay (const delay) policy
+ | otherwise = recover e hs'
+
+
+
+-------------------------------------------------------------------------------
+-- | A version of 'recovering' that tries to run the action only a
+-- single time. The control will return immediately upon both success
+-- and failure. Useful for implementing retry logic in distributed
+-- queues and similar external-interfacing systems.
+stepping
+#if MIN_VERSION_exceptions(0, 6, 0)
+ :: (MonadIO m, MonadMask m)
+#else
+ :: (MonadIO m, MonadCatch m)
+#endif
+ => RetryPolicyM m
+ -- ^ Just use 'retryPolicyDefault' for default settings
+ -> [(RetryStatus -> Handler m Bool)]
+ -- ^ Should a given exception be retried? Action will be
+ -- retried if this returns True *and* the policy allows it.
+ -- This action will be consulted first even if the policy
+ -- later blocks it.
+ -> (RetryStatus -> m ())
+ -- ^ Action to run with updated status upon failure.
+ -> (RetryStatus -> m a)
+ -- ^ Main action to perform with current status.
+ -> RetryStatus
+ -- ^ Current status of this step
+ -> m (Maybe a)
+stepping policy hs schedule f s = do
+ r <- try $ f s
+ case r of
+ Right x -> return $ Just x
+ Left e -> recover (e :: SomeException) hs
+ where
+ recover e [] = throwM e
+ recover e ((($ s) -> Handler h) : hs')
+ | Just e' <- fromException e = do
+ chk <- h e'
+ case chk of
+ True -> do
+ res <- applyPolicy policy s
+ case res of
+ Just rs -> do
+ schedule $! rs
+ return Nothing
+ Nothing -> throwM e'
+ False -> throwM e'
+ | otherwise = recover e hs'
+
+
+-------------------------------------------------------------------------------
+-- | Helper function for constructing handler functions of the form required
+-- by 'recovering'.
+logRetries
+ :: ( Monad m
+ , Exception e)
+ => (e -> m Bool)
+ -- ^ Test for whether action is to be retried
+ -> (Bool -> e -> RetryStatus -> m ())
+ -- ^ How to report the generated warning message. Boolean is
+ -- whether it's being retried or crashed.
+ -> RetryStatus
+ -- ^ Retry number
+ -> Handler m Bool
+logRetries test reporter status = Handler $ \ err -> do
+ result <- test err
+ reporter result err status
+ return result
+
+-- | For use with 'logRetries'.
+defaultLogMsg :: (Exception e) => Bool -> e -> RetryStatus -> String
+defaultLogMsg shouldRetry err status =
+ "[retry:" <> iter <> "] Encountered " <> show err <> ". " <> nextMsg
+ where
+ iter = show $ rsIterNumber status
+ nextMsg = if shouldRetry then "Retrying." else "Crashing."
+
+
+-------------------------------------------------------------------------------
+-- | Run given policy up to N iterations and gather results. In the
+-- pair, the @Int@ is the iteration number and the @Maybe Int@ is the
+-- delay in microseconds.
+simulatePolicy :: Monad m => Int -> RetryPolicyM m -> m [(Int, Maybe Int)]
+simulatePolicy n (RetryPolicyM f) = flip evalStateT defaultRetryStatus $ forM [0..n] $ \i -> do
+ stat <- get
+ delay <- lift (f stat)
+ put $! stat
+ { rsIterNumber = i + 1
+ , rsCumulativeDelay = rsCumulativeDelay stat `boundedPlus` fromMaybe 0 delay
+ , rsPreviousDelay = delay
+ }
+ return (i, delay)
+
+
+-------------------------------------------------------------------------------
+-- | Run given policy up to N iterations and pretty print results on
+-- the console.
+simulatePolicyPP :: Int -> RetryPolicyM IO -> IO ()
+simulatePolicyPP n p = do
+ ps <- simulatePolicy n p
+ forM_ ps $ \ (iterNo, res) -> putStrLn $
+ show iterNo <> ": " <> maybe "Inhibit" ppTime res
+ putStrLn $ "Total cumulative delay would be: " <>
+ (ppTime $ boundedSum $ (mapMaybe snd) ps)
+
+
+-------------------------------------------------------------------------------
+ppTime :: (Integral a, Show a) => a -> String
+ppTime n | n < 1000 = show n <> "us"
+ | n < 1000000 = show ((fromIntegral n / 1000) :: Double) <> "ms"
+ | otherwise = show ((fromIntegral n / 1000) :: Double) <> "ms"
+
+-------------------------------------------------------------------------------
+-- Bounded arithmetic
+-------------------------------------------------------------------------------
+
+-- | Same as '+' on 'Int' but it maxes out at @'maxBound' :: 'Int'@ or
+-- @'minBound' :: 'Int'@ rather than rolling over
+boundedPlus :: Int -> Int -> Int
+boundedPlus i@(I# i#) j@(I# j#) = case addIntC# i# j# of
+ (# k#, 0# #) -> I# k#
+ (# _, _ #)
+ | maxBy abs i j < 0 -> minBound
+ | otherwise -> maxBound
+ where
+ maxBy f a b = if f a >= f b then a else b
+
+-- | Same as '*' on 'Int' but it maxes out at @'maxBound' :: 'Int'@ or
+-- @'minBound' :: 'Int'@ rather than rolling over
+boundedMult :: Int -> Int -> Int
+boundedMult i@(I# i#) j@(I# j#) = case mulIntMayOflo# i# j# of
+ 0# -> I# (i# *# j#)
+ _ | signum i * signum j < 0 -> minBound
+ | otherwise -> maxBound
+
+-- | Same as 'sum' on 'Int' but it maxes out at @'maxBound' :: 'Int'@ or
+-- @'minBound' :: 'Int'@ rather than rolling over
+boundedSum :: [Int] -> Int
+boundedSum = foldl' boundedPlus 0
+
+-- | Same as '^' on 'Int' but it maxes out at @'maxBound' :: 'Int'@ or
+-- @'MinBound' :: 'Int'@ rather than rolling over
+boundedPow :: Int -> Int -> Int
+boundedPow x0 y0
+ | y0 < 0 = error "Negative exponent"
+ | y0 == 0 = 1
+ | otherwise = f x0 y0
+ where
+ f x y
+ | even y = f (x `boundedMult` x) (y `quot` 2)
+ | y == 1 = x
+ | otherwise = g (x `boundedMult` x) ((y - 1) `quot` 2) x
+ g x y z
+ | even y = g (x `boundedMult` x) (y `quot` 2) z
+ | y == 1 = x `boundedMult` z
+ | otherwise = g (x `boundedMult` x) ((y - 1) `quot` 2) (x `boundedMult` z)
+
+-------------------------------------------------------------------------------
+-- Lens machinery
+-------------------------------------------------------------------------------
+-- Unexported type aliases to clean up the documentation
+type Lens s t a b = forall f. Functor f => (a -> f b) -> s -> f t
+
+type Lens' s a = Lens s s a a
+
+
+-------------------------------------------------------------------------------
+lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b
+lens sa sbt afb s = sbt s <$> afb (sa s)
+{-# INLINE lens #-}
+
+
+ ------------------
+ -- Simple Tests --
+ ------------------
+
+
+
+-- data TestException = TestException deriving (Show, Typeable)
+-- data AnotherException = AnotherException deriving (Show, Typeable)
+
+-- instance Exception TestException
+-- instance Exception AnotherException
+
+
+-- test = retrying retryPolicyDefault [h1,h2] f
+-- where
+-- f = putStrLn "Running action" >> throwM AnotherException
+-- h1 = Handler $ \ (e :: TestException) -> return False
+-- h2 = Handler $ \ (e :: AnotherException) -> return True
--- /dev/null
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+module Tests.Control.Retry
+ ( tests
+ ) where
+
+-------------------------------------------------------------------------------
+import Control.Applicative
+import Control.Concurrent
+import Control.Concurrent.STM as STM
+import qualified Control.Exception as EX
+import Control.Monad.Catch
+import Control.Monad.Identity
+import Control.Monad.IO.Class
+import Control.Monad.Writer.Strict
+import Data.Either
+import Data.IORef
+import Data.List
+import Data.Maybe
+import Data.Time.Clock
+import Data.Time.LocalTime ()
+import Data.Typeable
+import Hedgehog as HH
+import qualified Hedgehog.Gen as Gen
+import qualified Hedgehog.Range as Range
+import System.IO.Error
+import Test.Tasty
+import Test.Tasty.Hedgehog
+import Test.Tasty.HUnit (assertBool, testCase, (@?=))
+-------------------------------------------------------------------------------
+import Control.Retry
+-------------------------------------------------------------------------------
+
+
+tests :: TestTree
+tests = testGroup "Control.Retry"
+ [ recoveringTests
+ , monoidTests
+ , retryStatusTests
+ , quadraticDelayTests
+ , policyTransformersTests
+ , maskingStateTests
+ , capDelayTests
+ , limitRetriesByCumulativeDelayTests
+ , overridingDelayTests
+ ]
+
+
+-------------------------------------------------------------------------------
+recoveringTests :: TestTree
+recoveringTests = testGroup "recovering"
+ [ testProperty "recovering test without quadratic retry delay" $ property $ do
+ startTime <- liftIO getCurrentTime
+ timeout <- forAll (Gen.int (Range.linear 0 15))
+ retries <- forAll (Gen.int (Range.linear 0 50))
+ res <- liftIO $ try $ recovering
+ (constantDelay timeout <> limitRetries retries)
+ testHandlers
+ (const $ throwM (userError "booo"))
+ endTime <- liftIO getCurrentTime
+ HH.assert (isLeftAnd isUserError res)
+ let ms' = (fromInteger . toInteger $ (timeout * retries)) / 1000000.0
+ HH.assert (diffUTCTime endTime startTime >= ms')
+ , testGroup "exception hierarchy semantics"
+ [ testCase "does not catch async exceptions" $ do
+ counter <- newTVarIO (0 :: Int)
+ done <- newEmptyMVar
+ let work = atomically (modifyTVar' counter succ) >> threadDelay 1000000
+
+ tid <- forkIO $
+ recoverAll (limitRetries 2) (const work) `finally` putMVar done ()
+
+ atomically (STM.check . (== 1) =<< readTVar counter)
+ EX.throwTo tid EX.UserInterrupt
+
+ takeMVar done
+
+ count <- atomically (readTVar counter)
+ count @?= 1
+
+ , testCase "recovers from custom exceptions" $ do
+ f <- mkFailN Custom1 2
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 3)
+ [const $ Handler $ \ Custom1 -> return shouldRetry]
+ f
+ (res :: Either Custom1 ()) @?= Right ()
+
+ , testCase "fails beyond policy using custom exceptions" $ do
+ f <- mkFailN Custom1 3
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 2)
+ [const $ Handler $ \ Custom1 -> return shouldRetry]
+ f
+ (res :: Either Custom1 ()) @?= Left Custom1
+
+ , testCase "recoverAll won't catch exceptions which are not decendants of SomeException" $ do
+ f <- mkFailN Custom1 4
+ res <- try $ recoverAll
+ (constantDelay 5000 <> limitRetries 3)
+ f
+ (res :: Either Custom1 ()) @?= Left Custom1
+
+ , testCase "does not recover from unhandled exceptions" $ do
+ f <- mkFailN Custom2 2
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 5)
+ [const $ Handler $ \ Custom1 -> return shouldRetry]
+ f
+ (res :: Either Custom2 ()) @?= Left Custom2
+
+
+ , testCase "recovers in presence of multiple handlers" $ do
+ f <- mkFailN Custom2 2
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 5)
+ [ const $ Handler $ \ Custom1 -> return shouldRetry
+ , const $ Handler $ \ Custom2 -> return shouldRetry ]
+ f
+ (res :: Either Custom2 ()) @?= Right ()
+
+
+ , testCase "general exceptions catch specific ones" $ do
+ f <- mkFailN Custom2 2
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 5)
+ [ const $ Handler $ \ (_::SomeException) -> return shouldRetry ]
+ f
+ (res :: Either Custom2 ()) @?= Right ()
+
+
+ , testCase "(redundant) even general catchers don't go beyond policy" $ do
+ f <- mkFailN Custom2 3
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 2)
+ [ const $ Handler $ \ (_::SomeException) -> return shouldRetry ]
+ f
+ (res :: Either Custom2 ()) @?= Left Custom2
+
+
+ , testCase "rethrows in presence of failed exception casts" $ do
+ f <- mkFailN Custom2 3
+ final <- try $ do
+ res <- try $ recovering
+ (constantDelay 5000 <> limitRetries 2)
+ [ const $ Handler $ \ (_::SomeException) -> return shouldRetry ]
+ f
+ (res :: Either Custom1 ()) @?= Left Custom1
+ final @?= Left Custom2
+ ]
+ ]
+
+
+-------------------------------------------------------------------------------
+monoidTests :: TestTree
+monoidTests = testGroup "Policy is a monoid"
+ [ testProperty "left identity" $ property $
+ propIdentity (\p -> mempty <> p) id
+ , testProperty "right identity" $ property $
+ propIdentity (\p -> p <> mempty) id
+ , testProperty "associativity" $ property $
+ propAssociativity (\x y z -> x <> (y <> z)) (\x y z -> (x <> y) <> z)
+ ]
+ where
+ propIdentity left right = do
+ retryStatus <- forAll genRetryStatus
+ fixedDelay <- forAll (Gen.maybe (Gen.int (Range.linear 0 maxBound)))
+ let calculateDelay _rs = fixedDelay
+ let applyPolicy' f = getRetryPolicyM (f $ retryPolicy calculateDelay) retryStatus
+ validRes = maybe True (>= 0)
+ l <- liftIO $ applyPolicy' left
+ r <- liftIO $ applyPolicy' right
+ if validRes r && validRes l
+ then l === r
+ else return ()
+ propAssociativity left right = do
+ retryStatus <- forAll genRetryStatus
+ let genDelay = Gen.maybe (Gen.int (Range.linear 0 maxBound))
+ delayA <- forAll genDelay
+ delayB <- forAll genDelay
+ delayC <- forAll genDelay
+ let applyPolicy' f = liftIO $ getRetryPolicyM (f (retryPolicy (const delayA)) (retryPolicy (const delayB)) (retryPolicy (const delayC))) retryStatus
+ res <- liftIO (liftA2 (==) (applyPolicy' left) (applyPolicy' right))
+ assert res
+
+
+-------------------------------------------------------------------------------
+retryStatusTests :: TestTree
+retryStatusTests = testGroup "retry status"
+ [ testCase "passes the correct retry status each time" $ do
+ let policy = limitRetries 2 <> constantDelay 100
+ rses <- gatherStatuses policy
+ rsIterNumber <$> rses @?= [0, 1, 2]
+ rsCumulativeDelay <$> rses @?= [0, 100, 200]
+ rsPreviousDelay <$> rses @?= [Nothing, Just 100, Just 100]
+ ]
+
+
+-------------------------------------------------------------------------------
+policyTransformersTests :: TestTree
+policyTransformersTests = testGroup "policy transformers"
+ [ testProperty "always produces positive delay with positive constants (no rollover)" $ property $ do
+ delay <- forAll (Gen.int (Range.linear 0 maxBound))
+ let res = runIdentity (simulatePolicy 1000 (exponentialBackoff delay))
+ delays = catMaybes (snd <$> res)
+ mnDelay = if null delays
+ then Nothing
+ else Just (minimum delays)
+ case mnDelay of
+ Nothing -> return ()
+ Just n -> do
+ footnote (show n ++ " is not >= 0")
+ HH.assert (n >= 0)
+ , testProperty "positive, nonzero exponential backoff is always incrementing" $ property $ do
+ delay <- forAll (Gen.int (Range.linear 1 maxBound))
+ let res = runIdentity (simulatePolicy 1000 (limitRetriesByDelay maxBound (exponentialBackoff delay)))
+ delays = catMaybes (snd <$> res)
+ sort delays === delays
+ length (group delays) === length delays
+ ]
+
+
+-------------------------------------------------------------------------------
+maskingStateTests :: TestTree
+maskingStateTests = testGroup "masking state"
+ [ testCase "shouldn't change masking state in a recovered action" $ do
+ maskingState <- EX.getMaskingState
+ final <- try $ recovering retryPolicyDefault testHandlers $ const $ do
+ maskingState' <- EX.getMaskingState
+ maskingState' @?= maskingState
+ fail "Retrying..."
+ assertBool
+ ("Expected EX.IOException but didn't get one")
+ (isLeft (final :: Either EX.IOException ()))
+
+ , testCase "should mask asynchronous exceptions in exception handlers" $ do
+ let checkMaskingStateHandlers =
+ [ const $ Handler $ \(_ :: SomeException) -> do
+ maskingState <- EX.getMaskingState
+ maskingState @?= EX.MaskedInterruptible
+ return shouldRetry
+ ]
+ final <- try $ recovering retryPolicyDefault checkMaskingStateHandlers $ const $ fail "Retrying..."
+ assertBool
+ ("Expected EX.IOException but didn't get one")
+ (isLeft (final :: Either EX.IOException ()))
+ ]
+
+
+-------------------------------------------------------------------------------
+capDelayTests :: TestTree
+capDelayTests = testGroup "capDelay"
+ [ testProperty "respects limitRetries" $ property $ do
+ retries <- forAll (Gen.int (Range.linear 1 100))
+ cap <- forAll (Gen.int (Range.linear 1 maxBound))
+ let policy = capDelay cap (limitRetries retries)
+ let delays = runIdentity (simulatePolicy (retries + 1) policy)
+ let Just lastDelay = lookup (retries - 1) delays
+ let Just gaveUp = lookup retries delays
+ let noDelay = 0
+ lastDelay === Just noDelay
+ gaveUp === Nothing
+ , testProperty "does not allow any delays higher than the given delay" $ property $ do
+ cap <- forAll (Gen.int (Range.linear 1 maxBound))
+ baseDelay <- forAll (Gen.int (Range.linear 1 100))
+ basePolicy <- forAllWith (const "RetryPolicy") (genScalingPolicy baseDelay)
+ let policy = capDelay cap basePolicy
+ let delays = catMaybes (snd <$> runIdentity (simulatePolicy 100 policy))
+ let baddies = filter (> cap) delays
+ baddies === []
+ ]
+
+
+-------------------------------------------------------------------------------
+-- | Generates policies that increase on each iteration
+genScalingPolicy :: (Alternative m) => Int -> m (RetryPolicyM Identity)
+genScalingPolicy baseDelay =
+ (pure (exponentialBackoff baseDelay) <|> pure (fibonacciBackoff baseDelay))
+
+
+-------------------------------------------------------------------------------
+limitRetriesByCumulativeDelayTests :: TestTree
+limitRetriesByCumulativeDelayTests = testGroup "limitRetriesByCumulativeDelay"
+ [ testProperty "never exceeds the given cumulative delay" $ property $ do
+ baseDelay <- forAll (Gen.int (Range.linear 1 100))
+ basePolicy <- forAllWith (const "RetryPolicy") (genScalingPolicy baseDelay)
+ cumulativeDelayMax <- forAll (Gen.int (Range.linear 1 10000))
+ let policy = limitRetriesByCumulativeDelay cumulativeDelayMax basePolicy
+ let delays = catMaybes (snd <$> runIdentity (simulatePolicy 100 policy))
+ footnoteShow delays
+ let actualCumulativeDelay = sum delays
+ footnote (show actualCumulativeDelay <> " <= " <> show cumulativeDelayMax)
+ HH.assert (actualCumulativeDelay <= cumulativeDelayMax)
+
+ ]
+
+-------------------------------------------------------------------------------
+quadraticDelayTests :: TestTree
+quadraticDelayTests = testGroup "quadratic delay"
+ [ testProperty "recovering test with quadratic retry delay" $ property $ do
+ startTime <- liftIO getCurrentTime
+ timeout <- forAll (Gen.int (Range.linear 0 15))
+ retries <- forAll (Gen.int (Range.linear 0 8))
+ res <- liftIO $ try $ recovering
+ (exponentialBackoff timeout <> limitRetries retries)
+ [const $ Handler (\(_::SomeException) -> return True)]
+ (const $ throwM (userError "booo"))
+ endTime <- liftIO getCurrentTime
+ HH.assert (isLeftAnd isUserError res)
+ let tmo = if retries > 0 then timeout * 2 ^ (retries - 1) else 0
+ let ms' = ((fromInteger . toInteger $ tmo) / 1000000.0)
+ HH.assert (diffUTCTime endTime startTime >= ms')
+ ]
+
+
+-------------------------------------------------------------------------------
+overridingDelayTests :: TestTree
+overridingDelayTests = testGroup "overriding delay"
+ [ testGroup "actual delays don't exceed specified delays"
+ [ testProperty "retryingDynamic" $
+ testOverride
+ retryingDynamic
+ (\delays rs _ -> return $ ConsultPolicyOverrideDelay (delays !! rsIterNumber rs))
+ (\_ _ -> liftIO getCurrentTime >>= \time -> tell [time])
+ , testProperty "recoveringDynamic" $
+ testOverride
+ recoveringDynamic
+ (\delays -> [\rs -> Handler (\(_::SomeException) -> return $ ConsultPolicyOverrideDelay (delays !! rsIterNumber rs))])
+ (\delays rs -> do
+ liftIO getCurrentTime >>= \time -> tell [time]
+ if rsIterNumber rs < length delays
+ then throwM (userError "booo")
+ else return ()
+ )
+ ]
+ ]
+ where
+ -- Transform a list of timestamps into a list of differences
+ -- between adjacent timestamps.
+ diffTimes = compareAdjacent (flip diffUTCTime)
+ microsToNominalDiffTime = toNominal . picosecondsToDiffTime . (* 1000000) . fromIntegral
+ toNominal :: DiffTime -> NominalDiffTime
+ toNominal = realToFrac
+ -- Generic test case used to test both "retryingDynamic" and "recoveringDynamic"
+ testOverride retryer handler action = property $ do
+ retryPolicy' <- forAll $ genPolicyNoLimit (Range.linear 1 1000000)
+ delays <- forAll $ Gen.list (Range.linear 1 10) (Gen.int (Range.linear 10 1000))
+ (_, measuredTimestamps) <- liftIO $ runWriterT $ retryer
+ -- Stop retrying when we run out of delays
+ (retryPolicy' <> limitRetries (length delays))
+ (handler delays)
+ (action delays)
+ let expectedDelays = map microsToNominalDiffTime delays
+ forM_ (zip (diffTimes measuredTimestamps) expectedDelays) $
+ \(actual, expected) -> diff actual (>=) expected
+
+-------------------------------------------------------------------------------
+isLeftAnd :: (a -> Bool) -> Either a b -> Bool
+isLeftAnd f ei = case ei of
+ Left v -> f v
+ _ -> False
+
+testHandlers :: [a -> Handler IO Bool]
+testHandlers = [const $ Handler (\(_::SomeException) -> return shouldRetry)]
+
+-- | Apply a function to adjacent list items.
+--
+-- Ie.:
+-- > compareAdjacent f [a0, a1, a2, a3, ..., a(n-2), a(n-1), an] =
+-- > [f a0 a1, f a1 a2, f a2 a3, ..., f a(n-2) a(n-1), f a(n-1) an]
+--
+-- Not defined for lists of length < 2.
+compareAdjacent :: (a -> a -> b) -> [a] -> [b]
+compareAdjacent f lst =
+ reverse . snd $ foldl
+ (\(a1, accum) a2 -> (a2, f a1 a2 : accum))
+ (head lst, [])
+ (tail lst)
+
+data Custom1 = Custom1 deriving (Eq,Show,Read,Ord,Typeable)
+data Custom2 = Custom2 deriving (Eq,Show,Read,Ord,Typeable)
+
+
+instance Exception Custom1
+instance Exception Custom2
+
+
+-------------------------------------------------------------------------------
+genRetryStatus :: MonadGen m => m RetryStatus
+genRetryStatus = do
+ n <- Gen.int (Range.linear 0 maxBound)
+ d <- Gen.int (Range.linear 0 maxBound)
+ l <- Gen.maybe (Gen.int (Range.linear 0 d))
+ return $ defaultRetryStatus { rsIterNumber = n
+ , rsCumulativeDelay = d
+ , rsPreviousDelay = l}
+
+
+-------------------------------------------------------------------------------
+-- | Generate an arbitrary 'RetryPolicy' without any limits applied.
+genPolicyNoLimit
+ :: (MonadGen mg, MonadIO mr)
+ => Range Int
+ -> mg (RetryPolicyM mr)
+genPolicyNoLimit durationRange =
+ Gen.choice
+ [ genConstantDelay
+ , genExponentialBackoff
+ , genFullJitterBackoff
+ , genFibonacciBackoff
+ ]
+ where
+ genDuration = Gen.int durationRange
+ -- Retry policies
+ genConstantDelay = fmap constantDelay genDuration
+ genExponentialBackoff = fmap exponentialBackoff genDuration
+ genFullJitterBackoff = fmap fullJitterBackoff genDuration
+ genFibonacciBackoff = fmap fibonacciBackoff genDuration
+
+-- Needed to generate a 'RetryPolicyM' using 'forAll'
+instance Show (RetryPolicyM m) where
+ show = const "RetryPolicyM"
+
+
+-------------------------------------------------------------------------------
+-- | Create an action that will fail exactly N times with the given
+-- exception and will then return () in any subsequent calls.
+mkFailN :: (Exception e) => e -> Int -> IO (s -> IO ())
+mkFailN e n = do
+ r <- newIORef 0
+ return $ const $ do
+ old <- atomicModifyIORef' r $ \ old -> (old+1, old)
+ case old >= n of
+ True -> return ()
+ False -> throwM e
+
+
+-------------------------------------------------------------------------------
+gatherStatuses
+ :: MonadIO m
+ => RetryPolicyM (WriterT [RetryStatus] m)
+ -> m [RetryStatus]
+gatherStatuses policy = execWriterT $
+ retrying policy (\_ _ -> return shouldRetry)
+ (\rs -> tell [rs])
+
+
+-------------------------------------------------------------------------------
+-- | Just makes things a bit easier to follow instead of a magic value
+-- of @return True@
+shouldRetry :: Bool
+shouldRetry = True
projects / haskell-retry.git / commitdiff