address CCACHE-67 by applying patch from dharrigan

Signed-off-by: Sean Corfield <sean@corfield.org>

Author: seancorfield

README.md

@@ -174,6 +174,7 @@ Change Log
 ====================
 
 * Release 1.2.next in progress
+  * [CCACHE-67](http://clojure.atlassian.net/browse/CCACHE-67) Add `clojure.core.cache.wrapped/size` function to get the size of the cache without dereferencing the atom. (via [@dharrigan](https://github.com/dharrigan)).
   * [CCACHE-65](http://clojure.atlassian.net/browse/CCACHE-65) Use `delay` in `lookup-or-miss` to avoid cache-stampede.
 * Release 1.1.234 on 2024-02-19
   * Update parent pom and `data.priority-map` versions

src/main/clojure/clojure/core/cache/wrapped.clj

@@ -76,6 +76,21 @@
   [cache-atom e]
   (c/has? @cache-atom e))
 
+(defn size
+  "Obtain the approximate size/count of the wrapped cache.
+
+  The value returned is a point-in-time approximate count/size as the nature
+  of certain caches don't reflect their true size until a 'lookup-or-miss'
+  operation is invoked - such as the TTL cache.
+
+  Whilst it is an approximate value, the returned result can be useful for
+  metric tracking or decision making.
+
+  Returns an approximate count/size of the wrapped cache.
+  "
+  [cache-atom]
+  (count @cache-atom))
+
 (defn hit
   "Is meant to be called if the cache is determined to contain a value
   associated with `e`.

src/test/clojure/clojure/core/cache/wrapped_test.clj

@@ -14,17 +14,25 @@
 (deftest basic-wrapped-test
   (let [cache (c/basic-cache-factory {})]
     (is (= nil (c/lookup cache :a)))
+    ;; the size of the cache is zero
+    (is (= 0 (c/size cache)))
     (is (= ::missing (c/lookup cache :a ::missing)))
     ;; mutating operation
     (is (= 42 (c/lookup-or-miss cache :a (constantly 42))))
     ;; cache now contains :a
     (is (= 42 (c/lookup cache :a)))
+    ;; and it now has a size of one
+    (is (= 1 (c/size cache)))
     ;; :a is present, does not call value-fn
     (is (= 42 (c/lookup-or-miss cache :a #(throw (ex-info "bad" {:key %})))))
     ;; cache still contains :a as 42
     (is (= 42 (c/lookup cache :a)))
+    ;; and it still has a size of one
+    (is (= 1 (c/size cache)))
     (c/evict cache :a)
     (is (= nil (c/lookup cache :a)))
+    ;; and the cache now has a size of zero
+    (is (= 0 (c/size cache)))
     (is (= ::missing (c/lookup cache :a ::missing)))))
 
 (deftest wrapped-ttl-test