retryable gem

Description

Runs a code block, and retries it when an exception occurs. It's great when working with flakey webservices (for example).

It's configured using four optional parameters :tries, :on, :sleep, :matching, :ensure, :exception_cb and runs the passed block. Should an exception occur, it'll retry for (n-1) times.

Should the number of retries be reached without success, the last exception will be raised.

Examples

Open an URL, retry up to two times when an OpenURI::HTTPError occurs.

require "open-uri"

Retryable.retryable(:tries => 3, :on => OpenURI::HTTPError) do
  xml = open("http://example.com/test.xml").read
end

Do something, retry up to four times for either ArgumentError or TimeoutError exceptions.

Retryable.retryable(:tries => 5, :on => [ArgumentError, TimeoutError]) do
  # some crazy code
end

Ensure that block of code is executed, regardless of whether an exception was raised. It doesn't matter if the block exits normally, if it retries to execute block of code, or if it is terminated by an uncaught exception -- the ensure block will get run.

f = File.open("testfile")

ensure_cb = Proc.new do |retries|
  puts "total retry attempts: #{retries}"

  f.close
end

Retryable.retryable(:ensure => ensure_cb) do
  # process file
end

Defaults

:tries => 2, :on => StandardError, :sleep => 1, :matching  => /.*/, :ensure => Proc.new { }, :exception_cb => Proc.new { }

Retryable also could be configured globally to change those defaults:

Retryable.configure do |config|
  config.ensure       = Proc.new {}
  config.exception_cb = Proc.new {}
  config.matching     = /.*/
  config.on           = StandardError
  config.sleep        = 1
  config.tries        = 2
end

Sleeping

By default Retryable waits for one second between retries. You can change this and even provide your own exponential backoff scheme.

Retryable.retryable(:sleep => 0) { }                     # don't pause at all between retries
Retryable.retryable(:sleep => 10) { }                    # sleep ten seconds between retries
Retryable.retryable(:sleep => lambda { |n| 4**n }) { }   # sleep 1, 4, 16, etc. each try

Matching error messages

You can also retry based on the exception message:

Retryable.retryable(:matching => /IO timeout/) do |retries, exception|
  raise "yo, IO timeout!" if retries == 0
end

Block Parameters

Your block is called with two optional parameters: the number of tries until now, and the most recent exception.

Retryable.retryable do |retries, exception|
  puts "try #{retries} failed with exception: #{exception}" if retries > 0
  pick_up_soap
end

Callback to run after an exception is rescued

exception_cb = Proc.new do |exception|
  # http://smartinez87.github.io/exception_notification
  ExceptionNotifier.notify_exception(exception, :data => {:message => "it failed"})
end

Retryable.retryable(:exception_cb => exception_cb) do
  # perform risky operation
end

You can temporary disable retryable blocks

Retryable.enabled?
=> true

Retryable.disable

Retryable.enabled?
=> false

Supported Ruby Versions

This library aims to support and is tested against the following Ruby versions:

• Ruby 1.8.7
• Ruby 1.9.2
• Ruby 1.9.3
• Ruby 2.0.0
• Ruby 2.1.2
• Ruby 2.2.0

If something doesn't work on one of these versions, it's a bug.

This library may inadvertently work (or seem to work) on other Ruby versions, however support will only be provided for the versions listed above.

If you would like this library to support another Ruby version or implementation, you may volunteer to be a maintainer.

Installation

Install the gem:

$ gem install retryable

Add it to your Gemfile:

gem 'retryable'

Thanks

Chu Yeow for this nifty piece of code

Scott Bronson