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# frozen_string_literal: true
# Like a hash, just does its best to stay in sync across the farm
# On boot all instances are blank, but they populate as various processes
# fill it up
require 'weakref'
require 'base64'
class DistributedCache
class Manager
CHANNEL_NAME ||= '/distributed_hash'.freeze
def initialize(message_bus = nil)
@subscribers = []
@subscribed = false
@lock = Mutex.new
@message_bus = message_bus || MessageBus
end
def subscribers
@subscribers
end
def process_message(message)
i = @subscribers.length - 1
payload = message.data
while i >= 0
begin
current = @subscribers[i]
next if payload["origin"] == current.identity && !Rails.env.test?
next if current.key != payload["hash_key"]
next if payload["discourse_version"] != Discourse.git_version
hash = current.hash(message.site_id)
case payload["op"]
when "set" then hash[payload["key"]] = payload["marshalled"] ? Marshal.load(Base64.decode64(payload["value"])) : payload["value"]
when "delete" then hash.delete(payload["key"])
when "clear" then hash.clear
end
rescue WeakRef::RefError
@subscribers.delete_at(i)
ensure
i -= 1
end
end
end
def ensure_subscribe!
return if @subscribed
@lock.synchronize do
return if @subscribed
@message_bus.subscribe(CHANNEL_NAME) do |message|
@lock.synchronize do
process_message(message)
end
end
@subscribed = true
end
end
def publish(hash, message)
message[:origin] = hash.identity
message[:hash_key] = hash.key
message[:discourse_version] = Discourse.git_version
@message_bus.publish(CHANNEL_NAME, message, user_ids: [-1])
end
def set(hash, key, value)
# special support for set
marshal = (Set === value || Hash === value || Array === value)
value = Base64.encode64(Marshal.dump(value)) if marshal
publish(hash, op: :set, key: key, value: value, marshalled: marshal)
end
def delete(hash, key)
publish(hash, op: :delete, key: key)
end
def clear(hash)
publish(hash, op: :clear)
end
def register(hash)
@lock.synchronize do
@subscribers << WeakRef.new(hash)
end
end
end
@default_manager = Manager.new
def self.default_manager
@default_manager
end
attr_reader :key
def initialize(key, manager: nil, namespace: true)
@key = key
@data = {}
@manager = manager || DistributedCache.default_manager
@namespace = namespace
@manager.ensure_subscribe!
@manager.register(self)
end
def identity
# fork resilient / multi machine identity
(@seed_id ||= SecureRandom.hex) + "#{Process.pid}"
end
def []=(k, v)
k = k.to_s if Symbol === k
@manager.set(self, k, v)
hash[k] = v
end
def [](k)
k = k.to_s if Symbol === k
hash[k]
end
def delete(k, publish: true)
k = k.to_s if Symbol === k
@manager.delete(self, k) if publish
hash.delete(k)
end
def clear
@manager.clear(self)
hash.clear
end
def hash(db = nil)
db =
if @namespace
db || RailsMultisite::ConnectionManagement.current_db
else
RailsMultisite::ConnectionManagement::DEFAULT
end
@data[db] ||= ThreadSafe::Hash.new
end
end