Commit 53783027 authored by Nick Thomas's avatar Nick Thomas

Add a ReactiveCaching concern for use in the KubernetesService

parent 7c2e16d0
# The ReactiveCaching concern is used to fetch some data in the background and
# store it in the Rails cache, keeping it up-to-date for as long as it is being
# requested. If the data hasn't been requested for +reactive_cache_lifetime+,
# it stop being refreshed, and then be removed.
#
# Example of use:
#
# class Foo < ActiveRecord::Base
# include ReactiveCaching
#
# self.reactive_cache_key = ->(thing) { ["foo", thing.id] }
#
# after_save :clear_reactive_cache!
#
# def calculate_reactive_cache
# # Expensive operation here. The return value of this method is cached
# end
#
# def result
# with_reactive_cache do |data|
# # ...
# end
# end
# end
#
# In this example, the first time `#result` is called, it will return `nil`.
# However, it will enqueue a background worker to call `#calculate_reactive_cache`
# and set an initial cache lifetime of ten minutes.
#
# Each time the background job completes, it stores the return value of
# `#calculate_reactive_cache`. It is also re-enqueued to run again after
# `reactive_cache_refresh_interval`, so keeping the stored value up to date.
# Calculations are never run concurrently.
#
# Calling `#result` while a value is in the cache will call the block given to
# `#with_reactive_cache`, yielding the cached value. It will also extend the
# lifetime by `reactive_cache_lifetime`.
#
# Once the lifetime has expired, no more background jobs will be enqueued and
# calling `#result` will again return `nil` - starting the process all over
# again
module ReactiveCaching
extend ActiveSupport::Concern
included do
class_attribute :reactive_cache_lease_timeout
class_attribute :reactive_cache_key
class_attribute :reactive_cache_lifetime
class_attribute :reactive_cache_refresh_interval
# defaults
self.reactive_cache_lease_timeout = 2.minutes
self.reactive_cache_refresh_interval = 1.minute
self.reactive_cache_lifetime = 10.minutes
def with_reactive_cache(&blk)
within_reactive_cache_lifetime do
data = Rails.cache.read(full_reactive_cache_key)
yield data if data.present?
end
ensure
Rails.cache.write(full_reactive_cache_key('alive'), true, expires_in: self.class.reactive_cache_lifetime)
ReactiveCachingWorker.perform_async(self.class, id)
end
def clear_reactive_cache!
Rails.cache.delete(full_reactive_cache_key)
end
def exclusively_update_reactive_cache!
locking_reactive_cache do
within_reactive_cache_lifetime do
enqueuing_update do
value = calculate_reactive_cache
Rails.cache.write(full_reactive_cache_key, value)
end
end
end
end
private
def full_reactive_cache_key(*qualifiers)
prefix = self.class.reactive_cache_key
prefix = prefix.call(self) if prefix.respond_to?(:call)
([prefix].flatten + qualifiers).join(':')
end
def locking_reactive_cache
lease = Gitlab::ExclusiveLease.new(full_reactive_cache_key, timeout: reactive_cache_lease_timeout)
uuid = lease.try_obtain
yield if uuid
ensure
Gitlab::ExclusiveLease.cancel(full_reactive_cache_key, uuid)
end
def within_reactive_cache_lifetime
yield if Rails.cache.read(full_reactive_cache_key('alive'))
end
def enqueuing_update
yield
ensure
ReactiveCachingWorker.perform_in(self.class.reactive_cache_refresh_interval, self.class, id)
end
end
end
class ReactiveCachingWorker
include Sidekiq::Worker
include DedicatedSidekiqQueue
def perform(class_name, id)
klass = begin
Kernel.const_get(class_name)
rescue NameError
nil
end
return unless klass
klass.find_by(id: id).try(:exclusively_update_reactive_cache!)
end
end
......@@ -46,5 +46,6 @@
- [repository_check, 1]
- [system_hook, 1]
- [git_garbage_collect, 1]
- [reactive_caching, 1]
- [cronjob, 1]
- [default, 1]
require 'spec_helper'
describe ReactiveCaching, caching: true do
include ReactiveCachingHelpers
class CacheTest
include ReactiveCaching
self.reactive_cache_key = ->(thing) { ["foo", thing.id] }
self.reactive_cache_lifetime = 5.minutes
self.reactive_cache_refresh_interval = 15.seconds
attr_reader :id
def initialize(id, &blk)
@id = id
@calculator = blk
end
def calculate_reactive_cache
@calculator.call
end
def result
with_reactive_cache do |data|
data / 2
end
end
end
let(:now) { Time.now.utc }
around(:each) do |example|
Timecop.freeze(now) { example.run }
end
let(:calculation) { -> { 2 + 2 } }
let(:cache_key) { "foo:666" }
let(:instance) { CacheTest.new(666, &calculation) }
describe '#with_reactive_cache' do
before { stub_reactive_cache }
subject(:go!) { instance.result }
context 'when cache is empty' do
it { is_expected.to be_nil }
it 'queues a background worker' do
expect(ReactiveCachingWorker).to receive(:perform_async).with(CacheTest, 666)
go!
end
it 'updates the cache lifespan' do
go!
expect(reactive_cache_alive?(instance)).to be_truthy
end
end
context 'when the cache is full' do
before { stub_reactive_cache(instance, 4) }
it { is_expected.to eq(2) }
context 'and expired' do
before { invalidate_reactive_cache(instance) }
it { is_expected.to be_nil }
end
end
end
describe '#clear_reactive_cache!' do
before do
stub_reactive_cache(instance, 4)
instance.clear_reactive_cache!
end
it { expect(instance.result).to be_nil }
end
describe '#exclusively_update_reactive_cache!' do
subject(:go!) { instance.exclusively_update_reactive_cache! }
context 'when the lease is free and lifetime is not exceeded' do
before { stub_reactive_cache(instance, "preexisting") }
it 'takes and releases the lease' do
expect_any_instance_of(Gitlab::ExclusiveLease).to receive(:try_obtain).and_return("000000")
expect(Gitlab::ExclusiveLease).to receive(:cancel).with(cache_key, "000000")
go!
end
it 'caches the result of #calculate_reactive_cache' do
go!
expect(read_reactive_cache(instance)).to eq(calculation.call)
end
it "enqueues a repeat worker" do
expect_reactive_cache_update_queued(instance)
go!
end
context 'and #calculate_reactive_cache raises an exception' do
before { stub_reactive_cache(instance, "preexisting") }
let(:calculation) { -> { raise "foo"} }
it 'leaves the cache untouched' do
expect { go! }.to raise_error("foo")
expect(read_reactive_cache(instance)).to eq("preexisting")
end
it 'enqueues a repeat worker' do
expect_reactive_cache_update_queued(instance)
expect { go! }.to raise_error("foo")
end
end
end
context 'when lifetime is exceeded' do
it 'skips the calculation' do
expect(instance).to receive(:calculate_reactive_cache).never
go!
end
end
context 'when the lease is already taken' do
before do
expect_any_instance_of(Gitlab::ExclusiveLease).to receive(:try_obtain).and_return(nil)
end
it 'skips the calculation' do
expect(instance).to receive(:calculate_reactive_cache).never
go!
end
end
end
end
module ReactiveCachingHelpers
def reactive_cache_key(subject, *qualifiers)
([subject.class.reactive_cache_key.call(subject)].flatten + qualifiers).join(':')
end
def stub_reactive_cache(subject = nil, data = nil)
allow(ReactiveCachingWorker).to receive(:perform_async)
allow(ReactiveCachingWorker).to receive(:perform_in)
write_reactive_cache(subject, data) if data
end
def read_reactive_cache(subject)
Rails.cache.read(reactive_cache_key(subject))
end
def write_reactive_cache(subject, data)
start_reactive_cache_lifetime(subject)
Rails.cache.write(reactive_cache_key(subject), data)
end
def reactive_cache_alive?(subject)
Rails.cache.read(reactive_cache_key(subject, 'alive'))
end
def invalidate_reactive_cache(subject)
Rails.cache.delete(reactive_cache_key(subject, 'alive'))
end
def start_reactive_cache_lifetime(subject)
Rails.cache.write(reactive_cache_key(subject, 'alive'), true)
end
def expect_reactive_cache_update_queued(subject)
expect(ReactiveCachingWorker).
to receive(:perform_in).
with(subject.class.reactive_cache_refresh_interval, subject.class, subject.id)
end
end
require 'spec_helper'
describe ReactiveCachingWorker do
let(:project) { create(:kubernetes_project) }
let(:service) { project.deployment_service }
subject { described_class.new.perform("KubernetesService", service.id) }
describe '#perform' do
it 'calls #exclusively_update_reactive_cache!' do
expect_any_instance_of(KubernetesService).to receive(:exclusively_update_reactive_cache!)
subject
end
end
end
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