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Try::Tiny::Retry(3) User Contributed Perl Documentation Try::Tiny::Retry(3)

Try::Tiny::Retry - Extends Try::Tiny to allow retries

version 0.004

Use just like Try::Tiny, but with "retry" instead of "try". By default, "retry" will try 10 times with exponential backoff:

    use Try::Tiny::Retry;

    retry     { ... }
    catch     { ... }
    finally   { ... };

You can retry only if the error matches some conditions:

    use Try::Tiny::Retry;

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

You can customize the number of tries and delay timing:

    use Try::Tiny::Retry ':all';

    retry     { ... }
    delay_exp { 5, 1e6 } # 5 tries, 1 second exponential-backoff
    catch     { ... };

You can run some code before each retry:

    use Try::Tiny::Retry;

    retry     { ... }
    on_retry  { ... }
    catch     { ... };

This module extends Try::Tiny to allow for retrying a block of code several times before failing. Otherwise, it works seamlessly like Try::Tiny.

By default, Try::Tiny::Retry exports "retry" and "retry_if", plus "try", "catch" and "finally" from Try::Tiny. You can optionally export "delay" or "delay_exp". Or you can get everything with the ":all" tag.

    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    { ... }
    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 $_ };

    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.

    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.

    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 )".

There are other retry modules on CPAN, but none of them worked seamlessly with Try::Tiny.
  • Action::Retry — OO (Moo) or functional; various delay strategies; supports conditions
  • AnyEvent::Retry — OO (Moose) and event-driven; various delay strategies
  • Attempt — functional; simple retry count with constant sleep time
  • Retry — OO (Moose) with fixed exponential backoff; supports callbacks on every iteration
  • Sub::Retry — functional; simple retry count with constant sleep time; supports conditions

Please report any bugs or feature requests through the issue tracker at <https://github.com/dagolden/Try-Tiny-Retry/issues>. You will be notified automatically of any progress on your issue.

This is open source software. The code repository is available for public review and contribution under the terms of the license.

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

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

David Golden <dagolden@cpan.org>

David Steinbrunner <dsteinbrunner@pobox.com>

This software is Copyright (c) 2013 by David Golden.

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004
2014-07-08 perl v5.32.1

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