added ref min/max history control - refs #138

1 files changed, 37 insertions, 2 deletions

diff --git a/src/clj/clojure/core.clj b/src/clj/clojure/core.clj
index ba674763..38c58daf 100644
--- a/src/clj/clojure/core.clj
+++ b/src/clj/clojure/core.clj
@@ -1268,14 +1268,30 @@
 
   :validator validate-fn
 
+  :min-history (default 0)
+  :max-history (default 10)
+
   If metadata-map is supplied, it will be come the metadata on the
   ref. validate-fn must be nil or a side-effect-free fn of one
   argument, which will be passed the intended new state on any state
   change. If the new state is unacceptable, the validate-fn should
   return false or throw an exception. validate-fn will be called on
-  transaction commit, when all refs have their final values."
+  transaction commit, when all refs have their final values.
+
+  Normally refs accumulate history dynamically as needed to deal with
+  read demands. If you know in advance you will need history you can
+  set :min-history to ensure it will be available when first needed (instead
+  of after a read fault). History is limited, and the limit can be set
+  with :max-history."
   ([x] (new clojure.lang.Ref x))
-  ([x & options] (setup-reference (ref x) options)))
+  ([x & options] 
+   (let [r  #^clojure.lang.Ref (setup-reference (ref x) options)
+         opts (apply hash-map options)]
+    (when (:max-history opts)
+      (.setMaxHistory r (:max-history opts)))
+    (when (:min-history opts)
+      (.setMinHistory r (:min-history opts)))
+    r)))
 
 (defn deref
   "Also reader macro: @ref/@agent/@var/@atom/@delay/@future. Within a transaction,
@@ -1383,6 +1399,25 @@
   [#^clojure.lang.Ref ref val]
     (. ref (set val)))
 
+(defn ref-history-count
+  "Returns the history count of a ref"
+  [#^clojure.lang.Ref ref]
+    (.getHistoryCount ref))
+
+(defn ref-min-history
+  "Gets the min-history of a ref, or sets it and returns the ref"
+  ([#^clojure.lang.Ref ref]
+    (.getMinHistory ref))
+  ([#^clojure.lang.Ref ref n]
+    (.setMinHistory ref n)))
+
+(defn ref-max-history
+  "Gets the max-history of a ref, or sets it and returns the ref"
+  ([#^clojure.lang.Ref ref]
+    (.getMaxHistory ref))
+  ([#^clojure.lang.Ref ref n]
+    (.setMaxHistory ref n)))
+
 (defn ensure
   "Must be called in a transaction. Protects the ref from modification
   by other transactions.  Returns the in-transaction-value of