Make connection pool fair with respect to waiting threads.

The core of this fix is a threadsafe, fair Queue class.  It is
very similar to Queue in stdlib except that it supports waiting
with a timeout.

The issue this solves is that if several threads are contending for
database connections, an unfair queue makes is possible that a thread
will timeout even while other threads successfully acquire and release
connections.  A fair queue means the thread that has been waiting the
longest will get the next available connection.

This includes a few test fixes to avoid test ordering issues that
cropped up during development of this patch.

1 files changed, 1 insertions, 1 deletions

diff --git a/activerecord/test/cases/connection_adapters/abstract_adapter_test.rb b/activerecord/test/cases/connection_adapters/abstract_adapter_test.rb
index 7dc6e8afcb..3e3d6e2769 100644
--- a/activerecord/test/cases/connection_adapters/abstract_adapter_test.rb
+++ b/activerecord/test/cases/connection_adapters/abstract_adapter_test.rb
@@ -36,7 +36,7 @@ module ActiveRecord
 
       def test_close
         pool = ConnectionPool.new(ConnectionSpecification.new({}, nil))
-        pool.connections << adapter
+        pool.insert_connection_for_test! adapter
         adapter.pool = pool
 
         # Make sure the pool marks the connection in use