Fix rack middleware so that it is threadsafe.

VCR as a whole is not designed to be threadsafe (running your tests in multiple threads is asking for trouble), but the rack middleware needs to be, since some rack servers (like WEBrick) are multithreaded.

Closes vcr#58.

CHANGELOG.md

@@ -9,6 +9,7 @@
 * Add `:ignore_cassettes` option to `VCR.turn_off!`.  This causes
   cassette insertions to be ignored rather than to trigger an error.
   Patch provided by [Justin Smestad](https://github.com/jsmestad).
+* Fix rack middleware to make it threadsafe.
 
 ## 1.9.0 (April 14, 2011)
 

lib/vcr/middleware/rack.rb

@@ -4,8 +4,10 @@ class Rack
       include Common
 
       def call(env)
-        VCR.use_cassette(*cassette_arguments(env)) do
-          @app.call(env)
+        Thread.exclusive do
+          VCR.use_cassette(*cassette_arguments(env)) do
+            @app.call(env)
+          end
         end
       end
     end

spec/vcr/middleware/rack_spec.rb

@@ -51,4 +51,24 @@
       instance.call(env_hash)
     end
   end
+
+  let(:threaded_app) do
+    lambda do |env|
+      sleep 0.15
+      VCR.send(:cassettes).should have(1).cassette
+      [200, {}, ['OK']]
+    end
+  end
+
+  it 'is thread safe' do
+    stack = described_class.new(threaded_app) do |cassette|
+      cassette.name 'c'
+    end
+
+    thread = Thread.new { stack.call({}) }
+    stack.call({})
+    thread.join
+
+    VCR.current_cassette.should be_nil
+  end
 end