ExecutionDeadline

Odds are, you should never ever, ever, use Ruby's built in timeout module unless you are 100% certain the wrapped code may be interrupted at any point. This gem provides a way to easily identify safe breakpoints for timeout operations.

Usage of this gem should be combined with the-ultimate-guide-to-ruby-timeouts to ensure your application releases resources from otherwise stuck threads.

Why use deadlines?

gRPC and Deadlines

Installation

Add this line to your application's Gemfile:

gem 'execution_deadline'

And then execute:

$ bundle

Or install it yourself as:

$ gem install execution_deadline

Usage

Deadline Enforcement

Deadlines are enforced only at breakpoints in the code specifically marked as safe to error. This is most easily done with the simple method wrappers provided in ExecutionDeadline::Helpers.

Examples

class SlowClass
  extend ExecutionDeadline::Helpers

  deadline in: 1
  def perform
    sub_method_1
    sub_method_1
    method_never_called
  end

  deadline runs_for: 0.6
  def sub_method_1
    sleep 0.7
  end

  def method_never_called; end
end

instance = SlowClass.new
instance.perform # Throws OutOfTime error since sub_method_1 takes 0.6s of
                 # the total allowed 1s execution time. Since only 0.4s
                 # is left, the second execution of sub_method_1 is prevented

When calculating time left after the execution of a method the actual execution time of the method is used. Consider the above example, but with a shorter actual execution time.

class ThinksItsSlowClass
  extend ExecutionDeadline::Helpers

  deadline in: 1
  def perform
    sub_method_1
    sub_method_1
    method_never_called
  end

  deadline runs_for: 0.6
  def sub_method_1
    sleep 0.1
  end

  def method_is_called
    :abcd
  end
end

instance = SlowClass.new
instance.perform # No errors are thrown and :abcd returned. Even though
                 # sub_method_1 says it will take 0.6 seconds, it actually
                 # takes 0.1 seconds. The second execution of sub_method_1 is
                 # checked against the remaining 0.9s, and allowed to continue

Deadlines are also usable on class methods and module methods.

class SlowClass
  extend ExecutionDeadline::Helpers

  deadline in: 1
  def self.perform
    sub_method_1
    sub_method_1
    method_never_called
  end

  deadline runs_for: 0.6
  def self.sub_method_1
    sleep 0.7
  end

  def self.method_never_called; end
end

SlowClass..perform # Throws OutOfTime error

module SlowModule
  extend ExecutionDeadline::Helpers

  deadline in: 1
  def self.perform
    sub_method_1
    sub_method_1
    method_never_called
  end

  deadline runs_for: 0.6
  def self.sub_method_1
    sleep 0.7
  end

  def self.method_never_called; end
end

SlowModule.perform # Throws OutOfTime error

Method interruption

Ruby's Timeout module is a bit heavy handed and could terminate operations at any point in your code flow. This gem is an attempt at marking interruption points at the start and end of slow methods. It should always be preferred to use a more graceful method, but sometimes a hammer is called for.

If you declare a deadline with interruptible: true. Ruby's Timeout module will be wrapped around your method set to timeout at the remaining deadline time. The error will be replaced with the value of raises or the built in classes.

Example

deadline runs_for: 0.6, interruptible: true
def self.sub_method_1
  sleep 0.7
end

Raised Errors

ExecutionDeadline::OutOfTime - Raised when a deadlined method is called but there is less time left then the expected runtime.

ExecutionDeadline::DeadlineExceeded - Raised when a deadlined method is and completed after the deadline time has passed.

All errors are subclasses of ExecutionDeadline::DeadlineError

Customizing Errors

The errors raised may be customized using the raises keyword. The error to be raised may only be set when the deadline is defined (using the in keyword)

module SlowModule
  class CustomError < StandardError; end
  extend ExecutionDeadline::Helpers

  deadline in: 1, raises: CustomError
  def self.runs_out_of_time
    sub_method_1
    sub_method_1
    method_never_called
  end

  deadline runs_for: 0.6
  def self.sub_method_1
    sleep 0.8
  end

  deadline in: 1, raises: CustomError
  def self.runs_over_time
    runs_over
    method_never_called
  end

  deadline runs_for: 0.5
  def self.runs_over
    sleep 1.1
  end

  def self.method_never_called; end
end

SlowModule.runs_out_of_time # Throws CustomError error in place of OutOfTime
SlowModule.runs_over_time # Throws CustomError error in place of DeadlineExceeded

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/execution_deadline. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the ExecutionDeadline project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

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