Stamina

Documentation

retry :: (MonadCatch m, MonadIO m) => RetrySettings -> (RetryStatus -> m a) -> m a

Retry on all sync exceptions, async exceptions will still be thrown.

The backoff delays between retries grow exponentially plus a random jitter. The backoff for retry attempt number _attempt_ is computed as:

   backoffExpBase ** (attempt - 1) + random(0, backoffJitter)

With the default values, the backoff for the first 5 attempts will be:

   2 ** 0 + random(0, 1) = 1 + random(0, 1)
   2 ** 1 + random(0, 1) = 2 + random(0, 1)
   2 ** 2 + random(0, 1) = 4 + random(0, 1)
   2 ** 3 + random(0, 1) = 8 + random(0, 1)
   2 ** 4 + random(0, 1) = 16 + random(0, 1)

If all retries fail, the last exception is let through.

retryFor :: (Exception exc, MonadIO m, MonadCatch m) => RetrySettings -> (exc -> m RetryAction) -> (RetryStatus -> m a) -> m a

data RetrySettings

Settings for the retry functions.

Constructors

RetrySettings

Fields

• initialRetryStatus :: RetryStatus

  Initial status of the retry, useful to override when resuming a retry

• maxAttempts :: Maybe Int

  Maximum number of attempts. Can be combined with a timeout. Default to 10.

• maxTime :: Maybe NominalDiffTime

  Maximum time for all retries. Can be combined with attempts. Default to 60s.

• backoffMaxRetryDelay :: Maybe NominalDiffTime

  Maximum backoff between retries at any time. Default to 60s.

• backoffJitter :: Double

  Maximum jitter that is added to retry back-off delays (the actual jitter added is a random number between 0 and backoffJitter). Defaults to 1.0.

• backoffExpBase :: Double

  The exponential base used to compute the retry backoff. Defaults to 2.0.

defaults :: RetrySettings

data RetryAction

Constructors

RaiseException

Retry

RetryDelay NominalDiffTime

RetryTime UTCTime

Instances

Show RetryAction

Defined in Stamina

Methods

showsPrec :: Int -> RetryAction -> ShowS

show :: RetryAction -> String

showList :: [RetryAction] -> ShowS

Eq RetryAction

Defined in Stamina

Methods

(==) :: RetryAction -> RetryAction -> Bool

(/=) :: RetryAction -> RetryAction -> Bool

data RetryStatus

Tracks the status of a retry

All fields will be zero if no retries have been attempted yet.

Constructors

RetryStatus

Fields

• attempts :: Int

  Number of retry attempts so far.

• delay :: NominalDiffTime

  Delay before the next retry.

• totalDelay :: NominalDiffTime

  Total delay so far.

• resetInitial :: IO ()

  Reset the retry status to the initial state.

• lastException :: Maybe SomeException

  The last exception that was thrown.

escalateWith :: Exception exc => (err -> exc) -> Either err a -> IO a

Escalate an Either to an exception by converting the Left value to an exception.

escalate :: Exception exc => Either exc a -> IO a

Escalate an Either to an exception.

withLeft :: a -> Maybe b -> Either a b

Convert a Maybe to an Either.