             let s2 = DispatchSemaphore(value: 0)
             // step
             // end
-            // COMMIT
+            // }
             
             let block1 = { () in
                 try! dbPool.read { db in

            // step
            // end
            // SELECT COUNT(*) FROM items -> 0
            
            let block1 = { () in
                try! dbPool.nonIsolatedRead { db in

                }
            }
            
            // Writer                       Reader
            // dbPool.write {
            // >
            //                              dbPool.readFromCurrentState {
            //                              <
            // INSERT INTO items (id) VALUES (NULL)
            // >
            let s1 = DispatchSemaphore(value: 0)
            // }                            SELECT COUNT(*) FROM persons -> 0
            //                              <
            let s2 = DispatchSemaphore(value: 0)
            //                              }
            
            var i: Int! = nil
            try dbPool.write { db in
                try dbPool.readFromCurrentState { db in
                    _ = s1.wait(timeout: .distantFuture)
