1 files changed, 11 insertions, 9 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 53dbbd8c21..627b753f01 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -506,14 +506,16 @@ module ActiveRecord
       # +conn+: an AbstractAdapter object, which was obtained by earlier by
       # calling #checkout on this pool.
       def checkin(conn)
-        synchronize do
-          remove_connection_from_thread_cache conn
+        conn.lock.synchronize do
+          synchronize do
+            remove_connection_from_thread_cache conn
 
-          conn._run_checkin_callbacks do
-            conn.expire
-          end
+            conn._run_checkin_callbacks do
+              conn.expire
+            end
 
-          @available.add conn
+            @available.add conn
+          end
         end
       end
 
@@ -677,7 +679,7 @@ module ActiveRecord
           # this block can't be easily moved into attempt_to_checkout_all_existing_connections's
           # rescue block, because doing so would put it outside of synchronize section, without
           # being in a critical section thread_report might become inaccurate
-          msg = "could not obtain ownership of all database connections in #{checkout_timeout} seconds"
+          msg = "could not obtain ownership of all database connections in #{checkout_timeout} seconds".dup
 
           thread_report = []
           @connections.each do |conn|
@@ -857,9 +859,9 @@ module ActiveRecord
     # All Active Record models use this handler to determine the connection pool that they
     # should use.
     #
-    # The ConnectionHandler class is not coupled with the Active models, as it has no knowlodge
+    # The ConnectionHandler class is not coupled with the Active models, as it has no knowledge
     # about the model. The model needs to pass a specification name to the handler,
-    # in order to lookup the correct connection pool.
+    # in order to look up the correct connection pool.
     class ConnectionHandler
       def initialize
         # These caches are keyed by spec.name (ConnectionSpecification#name).