Synchronize the lazy setters in Server

They're all at risk of races on the first requests.

actioncable/lib/action_cable/server/base.rb

+require 'thread'
+
 module ActionCable
   module Server
     # A singleton ActionCable::Server instance is available via ActionCable.server. It's used by the rack process that starts the cable server, but
@@ -13,7 +15,12 @@ class Base
       def self.logger; config.logger; end
       delegate :logger, to: :config
 
+      attr_reader :mutex
+
       def initialize
+        @mutex = Mutex.new
+
+        @remote_connections = @stream_event_loop = @worker_pool = @channel_classes = @pubsub = nil
       end
 
       # Called by rack to setup the server.
@@ -29,29 +36,31 @@ def disconnect(identifiers)
 
       # Gateway to RemoteConnections. See that class for details.
       def remote_connections
-        @remote_connections ||= RemoteConnections.new(self)
+        @remote_connections || @mutex.synchronize { @remote_connections ||= RemoteConnections.new(self) }
       end
 
       def stream_event_loop
-        @stream_event_loop ||= ActionCable::Connection::StreamEventLoop.new
+        @stream_event_loop || @mutex.synchronize { @stream_event_loop ||= ActionCable::Connection::StreamEventLoop.new }
       end
 
       # The thread worker pool for handling all the connection work on this server. Default size is set by config.worker_pool_size.
       def worker_pool
-        @worker_pool ||= ActionCable::Server::Worker.new(max_size: config.worker_pool_size)
+        @worker_pool || @mutex.synchronize { @worker_pool ||= ActionCable::Server::Worker.new(max_size: config.worker_pool_size) }
       end
 
       # Requires and returns a hash of all the channel class constants keyed by name.
       def channel_classes
-        @channel_classes ||= begin
-          config.channel_paths.each { |channel_path| require channel_path }
-          config.channel_class_names.each_with_object({}) { |name, hash| hash[name] = name.constantize }
+        @channel_classes || @mutex.synchronize do
+          @channel_classes ||= begin
+            config.channel_paths.each { |channel_path| require channel_path }
+            config.channel_class_names.each_with_object({}) { |name, hash| hash[name] = name.constantize }
+          end
         end
       end
 
       # Adapter used for all streams/broadcasting.
       def pubsub
-        @pubsub ||= config.pubsub_adapter.new(self)
+        @pubsub || @mutex.synchronize { @pubsub ||= config.pubsub_adapter.new(self) }
       end
 
       # All the identifiers applied to the connection class associated with this server.

actioncable/lib/action_cable/subscription_adapter/async.rb

@@ -4,8 +4,8 @@ module ActionCable
   module SubscriptionAdapter
     class Async < Inline # :nodoc:
       private
-        def subscriber_map
-          @subscriber_map ||= AsyncSubscriberMap.new
+        def new_subscriber_map
+          AsyncSubscriberMap.new
         end
 
         class AsyncSubscriberMap < SubscriberMap

actioncable/lib/action_cable/subscription_adapter/inline.rb

 module ActionCable
   module SubscriptionAdapter
     class Inline < Base # :nodoc:
+      def initialize(*)
+        super
+        @subscriber_map = nil
+      end
+
       def broadcast(channel, payload)
         subscriber_map.broadcast(channel, payload)
       end
@@ -19,7 +24,11 @@ def shutdown
 
       private
         def subscriber_map
-          @subscriber_map ||= SubscriberMap.new
+          @subscriber_map || @server.mutex.synchronize { @subscriber_map ||= new_subscriber_map }
+        end
+
+        def new_subscriber_map
+          SubscriberMap.new
         end
     end
   end

actioncable/lib/action_cable/subscription_adapter/postgresql.rb

@@ -5,6 +5,11 @@
 module ActionCable
   module SubscriptionAdapter
     class PostgreSQL < Base # :nodoc:
+      def initialize(*)
+        super
+        @listener = nil
+      end
+
       def broadcast(channel, payload)
         with_connection do |pg_conn|
           pg_conn.exec("NOTIFY #{pg_conn.escape_identifier(channel)}, '#{pg_conn.escape_string(payload)}'")
@@ -37,7 +42,7 @@ def with_connection(&block) # :nodoc:
 
       private
         def listener
-          @listener ||= Listener.new(self)
+          @listener || @server.mutex.synchronize { @listener ||= Listener.new(self) }
         end
 
         class Listener < SubscriberMap

actioncable/lib/action_cable/subscription_adapter/redis.rb

@@ -13,6 +13,11 @@ module SubscriptionAdapter
     class Redis < Base # :nodoc:
       @@mutex = Mutex.new
 
+      def initialize(*)
+        super
+        @redis_connection_for_broadcasts = @redis_connection_for_subscriptions = nil
+      end
+
       def broadcast(channel, payload)
         redis_connection_for_broadcasts.publish(channel, payload)
       end
@@ -35,15 +40,19 @@ def shutdown
       private
         def redis_connection_for_subscriptions
           ensure_reactor_running
-          @redis_connection_for_subscriptions ||= EM::Hiredis.connect(@server.config.cable[:url]).tap do |redis|
-            redis.on(:reconnect_failed) do
-              @logger.info "[ActionCable] Redis reconnect failed."
+          @redis_connection_for_subscriptions || @server.mutex.synchronize do
+            @redis_connection_for_subscriptions ||= EM::Hiredis.connect(@server.config.cable[:url]).tap do |redis|
+              redis.on(:reconnect_failed) do
+                @logger.info "[ActionCable] Redis reconnect failed."
+              end
             end
           end
         end
 
         def redis_connection_for_broadcasts
-          @redis_connection_for_broadcasts ||= ::Redis.new(@server.config.cable)
+          @redis_connection_for_broadcasts || @server.mutex.synchronize do
+            @redis_connection_for_broadcasts ||= ::Redis.new(@server.config.cable)
+          end
         end
 
         def ensure_reactor_running