diff --git a/lib/rest-core/promise/thread_pool.rb b/lib/rest-core/promise/thread_pool.rb
index <HASH>..<HASH> 100644
--- a/lib/rest-core/promise/thread_pool.rb
+++ b/lib/rest-core/promise/thread_pool.rb
@@ -1,4 +1,7 @@
 
+# reference implementation: puma
+# https://github.com/puma/puma/blob/v2.7.1/lib/puma/thread_pool.rb
+
 require 'thread'
 
 class RestCore::Promise::ThreadPool
puma's thread pool is the reference implementation

particularly:
<URL>