fix(ServerRendering) default pool_size of 1; document deadlock & therubyracer

Author: rmosolgo

README.md

@@ -188,7 +188,7 @@ You can configure your pool of JS virtual machines and specify where it should l
 # These are the defaults if you dont specify any yourself
 MyApp::Application.configure do
   # Settings for the pool of renderers:
-  config.react.server_renderer_pool_size  ||= 10
+  config.react.server_renderer_pool_size  ||= 1  # ExecJS doesn't allow more than one on MRI
   config.react.server_renderer_timeout    ||= 20 # seconds
   config.react.server_renderer = React::ServerRendering::SprocketsRenderer
   config.react.server_renderer_options = {
@@ -198,6 +198,10 @@ MyApp::Application.configure do
 end
 ```
 
+- On MRI, use `therubyracer` for the best performance (see [discussion](https://github.com/reactjs/react-rails/pull/290))
+- On MRI, you'll get a deadlock with `pool_size` > 1
+- If you're using JRuby, you can increase `pool_size` to have real multi-threaded rendering.
+
 ### Component generator
 
 `react-rails` ships with a Rails generator to help you get started with a simple component scaffold. 

lib/react/rails/railtie.rb

@@ -11,8 +11,8 @@ class Railtie < ::Rails::Railtie
       config.react.jsx_transform_options = {}
       config.react.jsx_transformer_class = nil # defaults to BabelTransformer
       # Server rendering:
-      config.react.server_renderer_pool_size  = 10
-      config.react.server_renderer_timeout    = 20 # seconds
+      config.react.server_renderer_pool_size  = 1   # increase if you're on JRuby
+      config.react.server_renderer_timeout    = 20  # seconds
       config.react.server_renderer            = nil # defaults to SprocketsRenderer
       config.react.server_renderer_options    = {}  # SprocketsRenderer provides defaults