retry

    retry    { ... }  # code that might fail
    retry_if { ... }  # conditions to be met for a retry
    delay    { ... }  # control repeats and intervals between retries
    catch    { ... }; # handler if all retries fail

The "retry" function works just like "try" from Try::Tiny, except that if an exception is thrown, the block may be executed again, depending on the "retry_if" and "delay" blocks.

If one or more "retry_if" blocks are provided, as long as any of them evaluate to true, a retry will be attempted unless the result of the "delay" block indicates otherwise. If none of them evaluate to true, no retry will be attempted and the "delay" block will not be called.

If no "delay" block is provided, the default will be 10 tries with a random delay up to 100 milliseconds with an exponential backoff. (See "delay_exp".) This has an expected cumulative delay of around 25 seconds if all retries fail.

retry_if

    retry    { ... }
    retry_if { /^could not connect/ }
    catch    { ... };

A "retry_if" block controls whether a retry should be attempted after an exception (assuming there are any retry attempts remaining).

The block is passed the cumulative number of attempts as an argument. The exception caught is provided in $_, just as with "catch". It should return a true value if a retry should be attempted.

Multiple "retry_if" blocks may be provided. Only one needs to evaluate to true to enable a retry.

Using a "retry_if" block based on the retry count is an alternate way to allow fewer (but not greater) tries than the default "delay" function, but with the default exponential backoff behavior. These are effectively equivalent:

    retry     { ... }
    retry_if  { shift() < 3 };

    retry     { ... }
    delay_exp { 3, 1e5 };

If you wish the exception to be rethrown if all "retry_if" blocks return false, you must use a "catch" block to do so:

    retry    { ... }
    retry_if { /^could not connect/ }
    catch    { die $_ };

on_retry

    retry    { ... }
    on_retry { $state->reset() }
    catch    { ... };

The "on_retry" block runs before each "retry" block after the first attempt. The exception caught is provided in $_. The block is passed the cumulative number of attempts as an argument. The return value is ignored.

Only one "on_retry" block is allowed.

delay

    retry { ... }
    delay {
        return if $_[0] >= 3; # only three tries
        sleep 1;              # constant delay between tries
    }
    catch { ... };

The "delay" block controls the number of attempts and the delay between attempts.

The block is passed the cumulative number of attempts as an argument. If the "delay" block returns an undefined value, no further retries will be made.

If you wish the exception to be rethrown if all attempts fail, you must use a "catch" block to do so:

    retry    { ... }
    delay    { ... }
    catch    { die $_ };

Only one "delay" block is allowed.

delay_exp

    retry     { ... }
    delay_exp { 3, 10000 } # 3 tries, 10000 µsec
    catch     { ... };

This function is an exponential-backoff delay-function generator. The delay between attempts is randomly selected between 0 and an upper bound. The upper bound doubles after each failure.

It requires a code block as an argument. The block will be evaluated in list context and must return two elements. The first element is the number of tries allowed. The second element is the starting upper bound in microseconds.

Given number of tries "N" and upper bound "U", the expected cumulative delay time if all attempts fail is "0.5 * U * ( 2^(N-1) - 1 )".

Bugs / Feature Requests

Source Code

<https://github.com/dagolden/Try-Tiny-Retry>

  git clone https://github.com/dagolden/Try-Tiny-Retry.git