Add schema cache to new connection pool after fork

Active Record detects when the process has forked and automatically
creates a new connection pool to avoid sharing file descriptors.

If the existing connection pool had a schema cache associated with it,
the new pool should copy it to avoid unnecessarily querying the database
for its schema.

The code to detect that the process has forked is in ConnectionHandler,
but the existing test for it was in the ConnectionManagement test file.
I moved it to the right place while I was writing the new test for this
change.

2 files changed, 46 insertions, 23 deletions

diff --git a/activerecord/test/cases/connection_adapters/connection_handler_test.rb b/activerecord/test/cases/connection_adapters/connection_handler_test.rb
index b72f8ca88c..9b1865e8bb 100644
--- a/activerecord/test/cases/connection_adapters/connection_handler_test.rb
+++ b/activerecord/test/cases/connection_adapters/connection_handler_test.rb
@@ -46,6 +46,52 @@ module ActiveRecord
       def test_connection_pools
         assert_equal([@pool], @handler.connection_pools)
       end
+
+      if Process.respond_to?(:fork)
+        def test_connection_pool_per_pid
+          object_id = ActiveRecord::Base.connection.object_id
+
+          rd, wr = IO.pipe
+          rd.binmode
+          wr.binmode
+
+          pid = fork {
+            rd.close
+            wr.write Marshal.dump ActiveRecord::Base.connection.object_id
+            wr.close
+            exit!
+          }
+
+          wr.close
+
+          Process.waitpid pid
+          assert_not_equal object_id, Marshal.load(rd.read)
+          rd.close
+        end
+
+        def test_retrieve_connection_pool_copies_schema_cache_from_ancestor_pool
+          @pool.schema_cache = @pool.connection.schema_cache
+          @pool.schema_cache.add('posts')
+
+          rd, wr = IO.pipe
+          rd.binmode
+          wr.binmode
+
+          pid = fork {
+            rd.close
+            pool = @handler.retrieve_connection_pool(@klass)
+            wr.write Marshal.dump pool.schema_cache.size
+            wr.close
+            exit!
+          }
+
+          wr.close
+
+          Process.waitpid pid
+          assert_equal @pool.schema_cache.size, Marshal.load(rd.read)
+          rd.close
+        end
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/connection_management_test.rb b/activerecord/test/cases/connection_management_test.rb
index bab624b78a..dff6ea0fb0 100644
--- a/activerecord/test/cases/connection_management_test.rb
+++ b/activerecord/test/cases/connection_management_test.rb
@@ -26,29 +26,6 @@ module ActiveRecord
         assert ActiveRecord::Base.connection_handler.active_connections?
       end
 
-      if Process.respond_to?(:fork)
-        def test_connection_pool_per_pid
-          object_id = ActiveRecord::Base.connection.object_id
-
-          rd, wr = IO.pipe
-          rd.binmode
-          wr.binmode
-
-          pid = fork {
-            rd.close
-            wr.write Marshal.dump ActiveRecord::Base.connection.object_id
-            wr.close
-            exit!
-          }
-
-          wr.close
-
-          Process.waitpid pid
-          assert_not_equal object_id, Marshal.load(rd.read)
-          rd.close
-        end
-      end
-
       def test_app_delegation
         manager = ConnectionManagement.new(@app)