cache_guard

cache_guard allows you to protect the execution of a block against concurrency.

Description

cache_guard makes use of your application cache store to ensure that there is no parallel execution of a given block of code. You can think of cache_guard as a simple distributed mutex that instead of blocking raises an error.

The best use case for cache_guard is granting synchronous access to a shared resource on asynchronous calls. For instance, you can use with the delayed_job gem to ensure that only one worker is accessing the shared resource and then rely on the delayed_job retries mechanism to execute the other workers.

Installation

This gem is available on RubyGems:

https://rubygems.org/gems/cache_guard

Usage

To use simply call the guard method passing a string that represents the shared resource and optionally a hash with options.

CacheGuard.guard("resource foo") { my_task_using_shared_resource }

Accepted options:

• default_value: The value that will be put in cache. The default value is 1;
• expires_in: This value must be greater than the maximum execution time of the block. Please note that after this time we'll not cancel the previous execution. The default value is 120 (seconds).
• cache_store: The ActiveSupport::Cache::Store instance that you want to use. By default we'll get this from Rails.cache.

CacheGuard can also be instantiated and used as follows.

cache_guard = CacheGuard.new("resource bar", { :expires_in => 180 })
cache_guard.guard { my_task_using_shared_resource }

CacheGuard raises a CacheGuard::AcquireError error on every failed attempt to acquire the guard on a given resource name.

Supported cache stores

CacheGuard uses the increment method from ActiveSupport::Cache::Store as a way to ensure atomic access to the shared resource. Since not all cache stores support this operation, we recommend that you test using the following code on your rails console:

Rails.cache.increment(SecureRandom.uuid, 1)
# => 1

We've successfully tested the following cache stores:

• Dalli v2.6.2
• Redis v4.0.0

You can also use FileStore on your development environment as long as you keep in mind that every call will gain access to the shared resource.

Contributing

Fork this repository and send a pull request.

To execute the test suite locally, use the following commands:

bundle install
bundle exec rspec

Versioning

This gem uses Semantic Versioning 2.0.0, which means:

Given a version number MAJOR.MINOR.PATCH, increment the:

1. MAJOR version when you make incompatible API changes,

2. MINOR version when you add functionality in a backwards-compatible manner, and

3. PATCH version when you make backwards-compatible bug fixes.

Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.