Maria-12648430 / wait_statem

wait_statem

wait_statem:enter_wait/2 must be the last call in a state call. It has not effect when it is not the last call, and it cannot be used in state enter calls.

wait_statem:enter_wait/2 changes the callback module and performs a state change. State and event timeouts are implicitly cancelled. Generic timeouts will keep running.

The arguments given to gen_statem:enter_wait/2 must be the calling module and a map or property list of the options listed below.

Options

• callback := Fun :: (atom() | fun((State :: term(), StateData0 :: term()) -> ok | {ok, StateData1 :: term()} | retry | {retry, StateData1 :: term()} | error | {error, StateData1 :: term()}) (mandatory).

  The callback function to try and retry, either as the name of a function in the module given to enter_wait/2 or an anonymous function. The arguments are the current state and data.

  • If the callback returns ok or an ok tuple, this is a success and the state machine transitions to the state given in the success_state option.
  • If retry or a retry tuple is returned, the callback is retried after the timeout defined by the strategy option. If the maximum number of attempts is exhausted, the state machine transitions to the state given in the error_state option.
  • If error or an error tuple is returned, this means giving up, and the state machine transitions to the state given in the error_state option.

• strategy := {simple, StrategyOpts :: (map() | proplists:proplist())} | {custom, {Fun :: (atom() | fun((Attempt :: non_neg_integer(), State :: term(), StateData0 :: term()) -> {ok, Timeout :: non_neg_integer()} | {ok, Timeout :: non_neg_integer(), StateData1 :: term()} | error | {error, StateData1 :: term()})}) (mandatory)

  Strategy used to calculate timeouts between retrying the function given in the callback option.

  The built-in simple strategy takes a map with the following options:

  • delay => non_neg_integer() (optional, default 0)

    Constant delay time in milliseconds.

  • time => non_neg_integer() (optional, default 0)

    Backoff base time in milliseconds.

  • backoff => number() (optional, default 0)

    Backoff exponent.

  • jitter => non_neg_integer() (optional, default 0)

    Random value between 0 and the given value which will be added to the timeout.

  • max => non_neg_integer() | infinity (optional, default infinity)

    Maximum number of attempts.

  The time between attempts is calculated as follows: delay + attempt^backoff * time + random(0 .. jitter).

  More advanced timeout strategies can be implemented by using the custom strategy, which takes a function that is given the current attempt, state and data as arguments.

• timing => relative | absolute (optional, default relative)

  Whether the calculated timeouts are to be related to the end of the previous attempt (relative) or to the start (absolute).

• success_state => State :: term() (optional, defaults to the state in which enter_wait/1 was called)

  State to transition to after success.

• error_state => term() (optional, defaults to the state in which enter_wait/1 was called)

  State to transition to when the maximum number of attempts is exhausted.