In process locking implemented, not sqlite locking.

scrbl/class.scrbl

@@ -83,6 +83,18 @@ Returns all keys.
 
 Returns all key-value pairs.
 }
+
+@defmethod[(with-lock [proc (-> any/c)]) any/c]{
+
+Calls @racket[proc] while holding the lock belonging to this keystore
+object and returns the value produced by @racket[proc]. Other threads
+using @method[keystore% with-lock] on the same object wait until the lock is
+released.
+
+The lock is reentrant for nested calls on the same thread and is
+released when control leaves @racket[proc], including when an exception
+is raised. Keystore methods do not acquire this lock automatically.
+}
 }
 
 @section{Examples}
@@ -115,4 +127,13 @@ Returns all key-value pairs.
 @racketblock[
 (send ks glob "*b*")
 (send ks glob-kv "*b*")
-]
+]
+
+@subsection{Locking}
+
+@racketblock[
+(send ks with-lock
+      (λ ()
+        (send ks set! 'counter
+              (add1 (send ks get 'counter 0)))))
+]