147 lines
4.4 KiB
Ruby
147 lines
4.4 KiB
Ruby
# frozen_string_literal: true
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# The ReactiveCaching concern is used to fetch some data in the background and
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# store it in the Rails cache, keeping it up-to-date for as long as it is being
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# requested. If the data hasn't been requested for +reactive_cache_lifetime+,
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# it stop being refreshed, and then be removed.
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#
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# Example of use:
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#
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# class Foo < ActiveRecord::Base
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# include ReactiveCaching
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#
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# self.reactive_cache_key = ->(thing) { ["foo", thing.id] }
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#
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# after_save :clear_reactive_cache!
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#
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# def calculate_reactive_cache
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# # Expensive operation here. The return value of this method is cached
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# end
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#
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# def result
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# with_reactive_cache do |data|
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# # ...
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# end
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# end
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# end
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#
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# In this example, the first time `#result` is called, it will return `nil`.
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# However, it will enqueue a background worker to call `#calculate_reactive_cache`
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# and set an initial cache lifetime of ten minutes.
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#
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# Each time the background job completes, it stores the return value of
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# `#calculate_reactive_cache`. It is also re-enqueued to run again after
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# `reactive_cache_refresh_interval`, so keeping the stored value up to date.
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# Calculations are never run concurrently.
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#
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# Calling `#result` while a value is in the cache will call the block given to
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# `#with_reactive_cache`, yielding the cached value. It will also extend the
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# lifetime by `reactive_cache_lifetime`.
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#
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# Once the lifetime has expired, no more background jobs will be enqueued and
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# calling `#result` will again return `nil` - starting the process all over
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# again
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module ReactiveCaching
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extend ActiveSupport::Concern
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InvalidateReactiveCache = Class.new(StandardError)
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included do
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class_attribute :reactive_cache_lease_timeout
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class_attribute :reactive_cache_key
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class_attribute :reactive_cache_lifetime
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class_attribute :reactive_cache_refresh_interval
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# defaults
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self.reactive_cache_lease_timeout = 2.minutes
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self.reactive_cache_refresh_interval = 1.minute
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self.reactive_cache_lifetime = 10.minutes
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def calculate_reactive_cache(*args)
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raise NotImplementedError
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end
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def reactive_cache_updated(*args)
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end
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def with_reactive_cache(*args, &blk)
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unless within_reactive_cache_lifetime?(*args)
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refresh_reactive_cache!(*args)
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return nil
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end
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keep_alive_reactive_cache!(*args)
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begin
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data = Rails.cache.read(full_reactive_cache_key(*args))
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yield data if data.present?
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rescue InvalidateReactiveCache
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refresh_reactive_cache!(*args)
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nil
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end
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end
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def clear_reactive_cache!(*args)
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Rails.cache.delete(full_reactive_cache_key(*args))
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Rails.cache.delete(alive_reactive_cache_key(*args))
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end
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def exclusively_update_reactive_cache!(*args)
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locking_reactive_cache(*args) do
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if within_reactive_cache_lifetime?(*args)
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enqueuing_update(*args) do
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key = full_reactive_cache_key(*args)
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new_value = calculate_reactive_cache(*args)
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old_value = Rails.cache.read(key)
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Rails.cache.write(key, new_value)
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reactive_cache_updated(*args) if new_value != old_value
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end
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end
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end
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end
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private
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def refresh_reactive_cache!(*args)
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clear_reactive_cache!(*args)
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keep_alive_reactive_cache!(*args)
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ReactiveCachingWorker.perform_async(self.class, id, *args)
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end
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def keep_alive_reactive_cache!(*args)
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Rails.cache.write(alive_reactive_cache_key(*args), true, expires_in: self.class.reactive_cache_lifetime)
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end
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def full_reactive_cache_key(*qualifiers)
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prefix = self.class.reactive_cache_key
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prefix = prefix.call(self) if prefix.respond_to?(:call)
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([prefix].flatten + qualifiers).join(':')
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end
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def alive_reactive_cache_key(*qualifiers)
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full_reactive_cache_key(*(qualifiers + ['alive']))
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end
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def locking_reactive_cache(*args)
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lease = Gitlab::ExclusiveLease.new(full_reactive_cache_key(*args), timeout: reactive_cache_lease_timeout)
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uuid = lease.try_obtain
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yield if uuid
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ensure
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Gitlab::ExclusiveLease.cancel(full_reactive_cache_key(*args), uuid)
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end
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def within_reactive_cache_lifetime?(*args)
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!!Rails.cache.read(alive_reactive_cache_key(*args))
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end
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def enqueuing_update(*args)
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yield
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ensure
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ReactiveCachingWorker.perform_in(self.class.reactive_cache_refresh_interval, self.class, id, *args)
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end
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end
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end
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