synced_folders/nfs: acquire process-level lock for export

CHANGELOG.md

@@ -30,6 +30,11 @@ IMPROVEMENTS:
   - guests/freebsd: Support for virtio interfaces. [GH-3082]
   - guests/openbsd: Support for virtio interfaces. [GH-3082]
 
+BUG FIXES:
+
+  - synced\_folders/nfs: Acquires a process-level lock so exports don't
+      collide with Vagrant running in parallel.
+
 PLUGIN AUTHOR CHANGES:
 
   - New host capability: "rdp\_client". This capability gets the RDP connection

plugins/synced_folders/nfs/synced_folder.rb

@@ -63,9 +63,16 @@ module VagrantPlugins
         # NFS exporting often requires sudo privilege and we don't want
         # overlapping input requests. [GH-2680]
         @@lock.synchronize do
+          begin
+            machine.env.lock("nfs-export") do
               machine.ui.info I18n.t("vagrant.actions.vm.nfs.exporting")
-          machine.env.host.capability(:nfs_export,
-            machine.ui, machine.id, machine_ip, folders)
+              machine.env.host.capability(
+                :nfs_export, machine.ui, machine.id, machine_ip, folders)
+            end
+          rescue Vagrant::Errors::EnvironmentLockedError
+            sleep 1
+            retry
+          end
         end
 
         # Mount