RUBY-932 Only use one lock in cluster

Author: estolfo

lib/mongo/cluster.rb

@@ -66,10 +66,10 @@ def add(host)
       if !addresses.include?(address)
         if addition_allowed?(address)
           log_debug([ "Adding #{address.to_s} to the cluster." ])
-          @addresses_update.synchronize { @addresses.push(address) }
+          @update_lock.synchronize { @addresses.push(address) }
           server = Server.new(address, event_listeners,
                               options.merge(slave_ok: @slave_ok))
-          @servers_update.synchronize { @servers.push(server) }
+          @update_lock.synchronize { @servers.push(server) }
           server
         end
       end
@@ -86,13 +86,12 @@ def add(host)
     # @since 2.0.0
     def initialize(seeds, options = {})
       @addresses = []
-      @addresses_update = Mutex.new
       @servers = []
-      @servers_update = Mutex.new
       @event_listeners = Event::Listeners.new
       @options = options.freeze
       @topology = Topology.initial(seeds, options)
       @slave_ok = @topology.single? unless options[:read]
+      @update_lock = Mutex.new
 
       subscribe_to(Event::DESCRIPTION_CHANGED, Event::DescriptionChanged.new(self))
       subscribe_to(Event::PRIMARY_ELECTED, Event::PrimaryElected.new(self))
@@ -152,11 +151,9 @@ def remove(host)
       log_debug([ "#{host} being removed from the cluster." ])
       address = Address.new(host)
       removed_servers = @servers.select { |s| s.address == address }
-      @servers_update.synchronize { @servers = @servers - removed_servers }
+      @update_lock.synchronize { @servers = @servers - removed_servers }
       removed_servers.each{ |server| server.disconnect! } if removed_servers
-      @addresses_update.synchronize do
-        @addresses.reject!{ |addr| addr == address }
-      end
+      @update_lock.synchronize { @addresses.reject! { |addr| addr == address } }
     end
 
     # Force a scan of all known servers in the cluster.
@@ -258,15 +255,15 @@ def addition_allowed?(address)
     end
 
     def servers_list
-      @servers_update.synchronize do
+      @update_lock.synchronize do
         @servers.reduce([]) do |servers, server|
           servers << server
         end
       end
     end
 
     def addresses_list
-      @addresses_update.synchronize do
+      @update_lock.synchronize do
         @addresses.reduce([]) do |addresses, address|
           addresses << address
         end