Module: Magick::RequestStoreIntegration

Defined in:
lib/magick/request_store_integration.rb

Overview

Per-request memoisation of Magick.enabled?.

Without it every call site re-evaluates the flag. That is merely wasteful for a deterministic flag, but wrong for a percentage-of-requests rollout: rand is re-rolled on every check, so two call sites rendering the same page can disagree about whether the feature is on.

Installed by prepending onto Magick's singleton class. enabled? is defined directly on that singleton class, so it precedes any included or extended module in the lookup chain — only a prepend can wrap it.

The Rails railtie installs this at boot. Outside Rails — a Sidekiq-only process, say — require this file and call install! yourself; the request_store gem ships middleware for Rack and for Sidekiq.

Constant Summary collapse

STORE_KEY =

Key the memo hash lives under inside RequestStore.

:magick_features

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.cache ⇒ Object

The memo hash for the request in flight, or nil when there is none.

nil means "do not cache". Outside a request — boot, a console, a rake task — nothing would ever clear the entries, so a memoised answer would outlive the moment that produced it. Answering live is the only safe behaviour there, and it is also what happens when the optional request_store gem is not installed at all.



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# File 'lib/magick/request_store_integration.rb', line 42

def cache
  return nil unless defined?(::RequestStore)
  return nil unless ::RequestStore.respond_to?(:active?) && ::RequestStore.active?

  ::RequestStore.store[STORE_KEY] ||= {}
end

.clear! ⇒ Object

Drops everything memoised for the request in flight. Call it after mutating a feature mid-request if later call sites in that same request must observe the new state.



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# File 'lib/magick/request_store_integration.rb', line 52

def clear!
  ::RequestStore.store.delete(STORE_KEY) if defined?(::RequestStore)
  nil
end

.install!(target = Magick) ⇒ Object

Idempotent. Returns true when it installed, false when already there.



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# File 'lib/magick/request_store_integration.rb', line 24

def install!(target = Magick)
  return false if installed?(target)

  target.singleton_class.prepend(self)
  true
end

.installed?(target = Magick) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/magick/request_store_integration.rb', line 31

def installed?(target = Magick)
  target.singleton_class.ancestors.include?(self)
end

Instance Method Details

#enabled?(feature_name, context = {}) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/magick/request_store_integration.rb', line 58

def enabled?(feature_name, context = {})
  cache = RequestStoreIntegration.cache
  return super unless cache

  key = [feature_name.to_s, context]
  # `key?` rather than a nil check: `false` is a perfectly good answer to memoise.
  return cache[key] if cache.key?(key)

  cache[key] = super
end