2 files changed, 20 insertions, 5 deletions
diff --git a/lib/puppet/node/environment.rb b/lib/puppet/node/environment.rb
index 762599cff..3f67474f9 100644
--- a/lib/puppet/node/environment.rb
+++ b/lib/puppet/node/environment.rb
@@ -1,4 +1,5 @@
 require 'puppet/util/cacher'
+require 'monitor'
 
 # Just define it, so this class has fewer load dependencies.
 class Puppet::Node
@@ -67,14 +68,23 @@ class Puppet::Node::Environment
 
   def initialize(name)
     @name = name
+    extend MonitorMixin
   end
 
   def known_resource_types
-    if @known_resource_types.nil? or @known_resource_types.stale?
-      @known_resource_types = Puppet::Resource::TypeCollection.new(self)
-      @known_resource_types.perform_initial_import
-    end
-    @known_resource_types
+    # This makes use of short circuit evaluation to get the right thread-safe
+    # per environment semantics with an efficient most common cases; we almost
+    # always just return our thread's known-resource types.  Only at the start
+    # of a compilation (after our thread var has been set to nil) or when the
+    # environment has changed do we delve deeper. 
+    Thread.current[:known_resource_types] = nil if (krt = Thread.current[:known_resource_types]) && krt.environment != self
+    Thread.current[:known_resource_types] ||= synchronize {
+      if @known_resource_types.nil? or @known_resource_types.stale?
+        @known_resource_types = Puppet::Resource::TypeCollection.new(self)
+        @known_resource_types.perform_initial_import
+      end
+      @known_resource_types
+    }
   end
 
   def module(name)
diff --git a/lib/puppet/parser/compiler.rb b/lib/puppet/parser/compiler.rb
index a901c0dd6..760d5a75a 100644
--- a/lib/puppet/parser/compiler.rb
+++ b/lib/puppet/parser/compiler.rb
@@ -15,6 +15,11 @@ class Puppet::Parser::Compiler
   include Puppet::Resource::TypeCollectionHelper
 
   def self.compile(node)
+    # At the start of a new compile we don't assume anything about 
+    # known_resouce_types; we'll get these from the environment and
+    # cache them in a thread variable for the duration of the 
+    # compilation.
+    Thread.current[:known_resource_types] = nil
     new(node).compile.to_resource
   rescue => detail
     puts detail.backtrace if Puppet[:trace]