Retryable
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 several optional parameters :tries, :on, :sleep, :matching, :ensure, :exception_cb, :not, :sleep_method 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.
Installation
Install the gem:
$ gem install retryable
Add it to your Gemfile:
gem 'retryable'
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
Try the block forever.
# For ruby versions prior to 1.9.2 use :infinite symbol instead
Retryable.retryable(tries: Float::INFINITY) do
# code here
end
Do something, retry up to four times for either ArgumentError or
Timeout::Error exceptions.
Retryable.retryable(tries: 5, on: [ArgumentError, Timeout::Error]) do
# code here
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 do |retries|
puts "total retry attempts: #{retries}"
f.close
end
Retryable.retryable(ensure: ensure_cb) do
# process file
end
Defaults
contexts: {},
ensure: proc { },
exception_cb: proc { },
log_method: proc { },
matching : /.*/,
not: [],
on: StandardError,
sleep: 1,
sleep_method: lambda { |n| Kernel.sleep(n) },
tries: 2
Retryable also could be configured globally to change those defaults:
Retryable.configure do |config|
config.contexts = {}
config.ensure = proc {}
config.exception_cb = proc {}
config.log_method = proc {}
config.matching = /.*/
config.not = []
config.on = StandardError
config.sleep = 1
config.sleep_method = Celluloid.method(:sleep)
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 "oops IO timeout!" if retries == 0
end
#matching param supports array format as well:
Retryable.retryable(matching: [/IO timeout/, "IO tymeout"]) do |retries, exception|
raise "oops 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
# code here
end
Callback to run after an exception is rescued
exception_cb = proc do |exception|
# http://smartinez87.github.io/exception_notification
ExceptionNotifier.notify_exception(exception, data: {message: "it failed"})
end
Retryable.retryable(exception_cb: exception_cb) do
# code here
end
Logging
# or extract it to global config instead:
log_method = lambda do |retries, exception|
Logger.new(STDOUT).debug("[Attempt ##{retries}] Retrying because [#{exception.class} - #{exception.}]: #{exception.backtrace.first(5).join(' | ')}")
end
Retryable.retryable(log_method: log_method, matching: /IO timeout/) do |retries, exception|
raise "oops IO timeout!" if retries == 0
end
#D, [2018-09-01T18:19:06.093811 #22535] DEBUG -- : [Attempt #1] Retrying because [RuntimeError - oops IO timeout!]: (irb#1):6:in `block in irb_binding' | /home/nikita/Projects/retryable/lib/retryable.rb:73:in `retryable' | (irb#1):6:in `irb_binding' | /home/nikita/.rvm/rubies/ruby-2.5.0/lib/ruby/2.5.0/irb/workspace.rb:85:in `eval' | /home/nikita/.rvm/rubies/ruby-2.5.0/lib/ruby/2.5.0/irb/workspace.rb:85:in `evaluate'
If you prefer to use Rails' native logger:
log_method = lambda do |retries, exception|
Rails.logger.debug("[Attempt ##{retries}] Retrying because [#{exception.class} - #{exception.}]: #{exception.backtrace.first(5).join(' | ')}")
end
Contexts
Contexts allow you to extract common Retryable.retryable calling options for reuse or readability purposes.
Retryable.configure do |config|
config.contexts[:faulty_service] = {
:on: [FaultyServiceTimeoutError],
:sleep: 10,
:tries: 5
}
end
Retryable.with_context(:faulty_service) {
# code here
}
You may also override options defined in your contexts:
# :on & sleep defined in the context earlier are still effective
Retryable.with_context(:faulty_service, tries: 999) {
# code here
}
You can temporary disable retryable blocks
Retryable.enabled?
=> true
Retryable.disable
Retryable.enabled?
=> false
Specify exceptions where a retry should NOT be performed
No more tries will be made if an exception listed in :not is raised.
Takes precedence over :on.
class MyError < StandardError; end
Retryable.retryable(tries: 5, on: [StandardError], not: [MyError]) do
raise MyError "No retries!"
end
Specify the sleep method to use
This can be very useful when you are working with Celluloid which implements its own version of the method sleep.
Retryable.retryable(sleep_method: Celluloid.method(:sleep)) do
# code here
end
Supported Ruby Versions
This library aims to support and is [tested against][travis] the following Ruby versions:
- Ruby 1.9.3
- Ruby 2.0.0
- Ruby 2.1.10
- Ruby 2.2.10
- Ruby 2.3.8
- Ruby 2.4.5
- Ruby 2.5.3
- Ruby 2.6.1
NOTE: if you need retryable to be running on Ruby 1.8 use gem versions prior to 3.0.0 release
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.