PLT Redex implementation of ClojureTxTk

This repository contains a machine-executable implementation of the operational semantics of ClojureTxTk, using PLT Redex.

It consists of the following files:

• clj-base.rkt defines Lb, the "base" language (based on Clojure)
• clj-futures.rkt defines Lf, the base language extended with support for futures (as in Clojure)
• clj-tx.rkt defines Lt, which is Lf extended with support for transactions (as in Clojure)
• tx-futs.rkt defines Ltf, which is Lt extended with support for transactional futures (not in Clojure)
• map.rkt: helper functions for maps
• set.rkt: helper functions for sets

Each of the files also contains test cases.

For instance, tx-futs.rkt contains the following test case (named example-tx-futs-3):

(let [(r_0 (ref 0))
      (f_0 (fork
             (atomic
               (let [(x (fork (ref-set r_0 (+ (deref r_0) 1))))
                     (y (fork (ref-set r_0 (+ (deref r_0) 2))))]
                 (do (join x) ; => r_0 = original + 1
                   (join y)   ; => r_0 = original + 2
                   (deref r_0)))))) ; => returns original + 2
       (f_1 (fork
              (atomic
                (let [(x (fork (ref-set r_0 (+ (deref r_0) 3))))
                      (y (fork (ref-set r_0 (+ (deref r_0) 4))))]
                  (do (join x) ; => r_0 = original + 3
                    (join y)   ; => r_0 = original + 4
                    (deref r_0))))))] ; => returns original + 4
  (+ (join f_0) (join f_1)))

There are two possible outcomes of this program:

(term [[(f_0 8) (f_new1 6) (f_new 2)]
       [(r_new 6) (r_new 5) (r_new 2) (r_new 1) (r_new 0)]])
(term [[(f_0 10) (f_new1 4) (f_new 6)]
       [(r_new 6) (r_new 5) (r_new 4) (r_new 3) (r_new 0)]])

These correspond to the two possible serializations: the first corresponds to transaction 1 executing first (end result is 8), the second to transaction 2 executing first (end result is 10).

These results can be visualized using:

(traces ->tf example-tx-futs-3)

This is shown in the image in example-tx-futs-3.pdf. You can see how different interleavings lead to different intermediate states, but they collapse into two final states, corresponding to the two possible serializations.