core: initialize synced folder class only once [GH-3067]

lib/vagrant/action/builtin/synced_folders.rb

@@ -53,19 +53,26 @@ module Vagrant
             end
           end
 
+          # Build up the instances of the synced folders. We do this once
+          # so that they can store state.
+          folders = folders.map do |impl_name, fs|
+            instance = plugins[impl_name.to_sym][0].new
+            [instance, impl_name, fs]
+          end
+
           # Go through each folder and prepare the folders
-          folders.each do |impl_name, fs|
+          folders.each do |impl, impl_name, fs|
             @logger.info("Invoking synced folder prepare for: #{impl_name}")
-            plugins[impl_name.to_sym][0].new.prepare(env[:machine], fs, impl_opts(impl_name, env))
+            impl.prepare(env[:machine], fs, impl_opts(impl_name, env))
           end
 
           # Continue, we need the VM to be booted.
           @app.call(env)
 
           # Once booted, setup the folder contents
-          folders.each do |impl_name, fs|
+          folders.each do |impl, impl_name, fs|
             @logger.info("Invoking synced folder enable: #{impl_name}")
-            plugins[impl_name.to_sym][0].new.enable(env[:machine], fs, impl_opts(impl_name, env))
+            impl.enable(env[:machine], fs, impl_opts(impl_name, env))
           end
         end
       end

test/unit/vagrant/action/builtin/synced_folders_test.rb

@@ -62,13 +62,16 @@ describe Vagrant::Action::Builtin::SyncedFolders do
     end
 
     it "should invoke prepare then enable" do
+      ids   = []
       order = []
       tracker = Class.new(impl(true, "good")) do
         define_method(:prepare) do |machine, folders, opts|
+          ids   << self.object_id
           order << :prepare
         end
 
         define_method(:enable) do |machine, folders, opts|
+          ids   << self.object_id
           order << :enable
         end
       end
@@ -89,6 +92,8 @@ describe Vagrant::Action::Builtin::SyncedFolders do
       subject.call(env)
 
       order.should == [:prepare, :enable]
+      expect(ids.length).to eq(2)
+      expect(ids[0]).to eq(ids[1])
     end
   end
 end