Manually call release on the prepared statements

The garbage collector will come back through later and release the
opaque nif resource. This will at least reclaim a large portion of the
memory taken up by the prepared statement.

Author: warmwaffles

lib/exqlite/connection.ex

@@ -259,7 +259,8 @@ defmodule Exqlite.Connection do
   This callback is called in the client process.
   """
   @impl true
-  def handle_close(_query, _opts, state) do
+  def handle_close(query, _opts, state) do
+    Sqlite3.release(state.db, query.ref)
     {:ok, nil, state}
   end
 
@@ -274,10 +275,8 @@ defmodule Exqlite.Connection do
   end
 
   @impl true
-  def handle_deallocate(%Query{} = _query, _cursor, _opts, state) do
-    # We actually don't need to do anything about the cursor. Since it is a
-    # prepared statement, it will be garbage collected by erlang when it loses
-    # references.
+  def handle_deallocate(%Query{} = query, _cursor, _opts, state) do
+    Sqlite3.release(state.db, query.ref)
     {:ok, nil, state}
   end
 

test/exqlite/connection_test.exs

@@ -188,4 +188,22 @@ defmodule Exqlite.ConnectionTest do
       assert {:ok, conn} == Connection.ping(conn)
     end
   end
+
+  describe ".handle_close/3" do
+    test "releases the underlying prepared statement" do
+      {:ok, conn} = Connection.connect(database: :memory)
+
+      {:ok, query, _result, conn} =
+        %Query{statement: "create table users (id integer primary key, name text)"}
+        |> Connection.handle_execute([], [], conn)
+
+      assert {:ok, nil, conn} == Connection.handle_close(query, [], conn)
+
+      {:ok, query, conn} =
+        %Query{statement: "select * from users where id < ?"}
+        |> Connection.handle_prepare([], conn)
+
+      assert {:ok, nil, conn} == Connection.handle_close(query, [], conn)
+    end
+  end
 end