Change ConnectionPool size to not use an iterator (#3015)

Author: mullermp

gems/aws-sdk-core/CHANGELOG.md

@@ -1,6 +1,8 @@
 Unreleased Changes
 ------------------
 
+* Issue - Fix issue where `ConnectionPool` size iteration would prevent a new key from being added to the pool.
+
 3.194.1 (2024-05-03)
 ------------------
 

gems/aws-sdk-core/lib/seahorse/client/net_http/connection_pool.rb

@@ -119,11 +119,7 @@ def session_for(endpoint, &block)
         #   pool, not counting those currently in use.
         def size
           @pool_mutex.synchronize do
-            size = 0
-            @pool.each_pair do |endpoint,sessions|
-              size += sessions.size
-            end
-            size
+            @pool.values.flatten.size
           end
         end