Make ClimateControl.modify re-entrant

lib/climate_control/environment.rb

@@ -7,10 +7,25 @@ class Environment
 
     def initialize
       @semaphore = Mutex.new
+      @owner = nil
     end
 
     def_delegators :env, :[]=, :to_hash, :[], :delete
-    def_delegator :@semaphore, :synchronize
+
+    def synchronize
+      if @owner == Thread.current
+        return yield if block_given?
+      end
+
+      @semaphore.synchronize do
+        begin
+          @owner = Thread.current
+          yield if block_given?
+        ensure
+          @owner = nil
+        end
+      end
+    end
 
     private
 

spec/acceptance/climate_control_spec.rb

@@ -111,6 +111,19 @@
     expect(ENV["BAZ"]).to be_nil
   end
 
+  it "is re-entrant" do
+    ret = with_modified_env(FOO: "foo") do
+      with_modified_env(BAR: "bar") do
+        "bar"
+      end
+    end
+
+    expect(ret).to eq("bar")
+
+    expect(ENV["FOO"]).to be_nil
+    expect(ENV["BAR"]).to be_nil
+  end
+
   it "raises when the value cannot be assigned properly" do
     Thing = Class.new
     message = generate_type_error_for_object(Thing.new)