txn: add reads and writes, require dom-top.

txn/project.clj

@@ -6,5 +6,6 @@
   :test-selectors {:default     (fn [m] (not (or (:perf m))))
                    :all         (fn [m] true)
                    :perf        :perf}
+  :dependencies [[dom-top "1.0.8"]]
   :profiles {:dev {:dependencies [[org.clojure/clojure "1.10.1"]
                                   [criterium "0.4.5"]]}})

txn/src/jepsen/txn.clj

@@ -1,6 +1,7 @@
 (ns jepsen.txn
   "Manipulates transactions. Transactions are represented as a sequence of
-  micro-operations (mops for short).")
+  micro-operations (mops for short)."
+  (:require [dom-top.core :refer [loopr]]))
 
 (defn reduce-mops
   "Takes a history of operations, where each operation op has a :value which is
@@ -21,6 +22,30 @@
   [history]
   (mapcat (fn [op] (map (fn [mop] [op mop]) (:value op))) history))
 
+(defn reads
+  "Given a transaction, returns a map of keys to sets of all values that
+  transaction read."
+  [txn]
+  (loopr [reads (transient {})]
+         [[f k v] txn]
+         (if (= :r f)
+           (let [vs (get reads k #{})]
+             (recur (assoc! reads k (conj vs v))))
+           (recur reads))
+         (persistent! reads)))
+
+(defn writes
+  "Given a transaction, returns a map of keys to sets of all values that
+  transaction wrote."
+  [txn]
+  (loopr [writes (transient {})]
+         [[f k v] txn]
+         (if (= :w f)
+           (let [vs (get writes k #{})]
+             (recur (assoc! writes k (conj vs v))))
+           (recur writes))
+         (persistent! writes)))
+
 (defn ext-reads
   "Given a transaction, returns a map of keys to values for its external reads:
   values that transaction observed which it did not write itself."