Clojure startup time hack: refer

gistfile1.diff

clojure.core/refer is relatively heavyweight.  It gets called 7 times during Clojure
 startup (4 times in 1.3.0).  There's potential to shave off 10% of the startup time
by improving it.  Probably even more for projects with a large number of small
namespaces.

This is just a quick experiment to see what's possible, it would need much refining.
It's not thread safe, doesn't print warnings and could probably be written more
elegantly.

java -Xbootclasspath/a:clojure.jar -cp clojure.jar clojure.main -e "(System/exit 0)"

master: 0.56 user 0.03 system 0:00.44 elapsed 136% CPU 189264k maxresident
 patch: 0.42 user 0.03 system 0:00.38 elapsed 118% CPU 178000k maxresident

diff --git a/src/clj/clojure/core.clj b/src/clj/clojure/core.clj
index e1aa2df..b747401 100644
--- a/src/clj/clojure/core.clj
+++ b/src/clj/clojure/core.clj
@@ -3743,6 +3743,11 @@
                                  (= ns (.ns v))))
                 (ns-map ns))))
 
+(defn var-public? [ns ^clojure.lang.Var v]
+  (and (instance? clojure.lang.Var v)
+       (= ns (.ns v))
+       (.isPublic v)))
+
 (defn refer
   "refers to all public vars of ns, subject to filters.
   filters can include at most one each of:
@@ -3759,7 +3764,22 @@
   to a symbol different from the var's name, in order to prevent
   clashes. Use :use in the ns macro in preference to calling this directly."
   {:added "1.0"}
-  [ns-sym & filters]
+  ;; quick and dirty hack at a fast path version
+  ;; beware: not thread safe and doesn't give var redefined
+  ;;         warnings.
+  ([ns-sym]
+     (let [ns (find-ns ns-sym)
+           nsmap (ns-map ns)
+           m (loop [src (ns-map ns)
+                    dst (transient (.getMappings *ns*))]
+               (if-let [entry (first src)]
+                 (let [sym (key entry)
+                       v (val entry)]
+                   (recur (rest src) (if (var-public? ns v)
+                                       (assoc! dst sym v) dst)))
+                 dst))]
+       (.setMappings *ns* (persistent! m))))
+  ([ns-sym & filters]
     (let [ns (or (find-ns ns-sym) (throw (new Exception (str "No namespace: " ns-sym))))
           fs (apply hash-map filters)
           nspublics (ns-publics ns)
@@ -3776,7 +3796,7 @@
                           (if (get (ns-interns ns) sym)
                             (str sym " is not public")
                             (str sym " does not exist")))))
-            (. *ns* (refer (or (rename sym) sym) v)))))))
+            (. *ns* (refer (or (rename sym) sym) v))))))))
 
 (defn ns-refers
   "Returns a map of the refer mappings for the namespace."
diff --git a/src/jvm/clojure/lang/Namespace.java b/src/jvm/clojure/lang/Namespace.java
index 0a4a38d..41aa2c6 100644
--- a/src/jvm/clojure/lang/Namespace.java
+++ b/src/jvm/clojure/lang/Namespace.java
@@ -192,6 +192,10 @@ public Object getMapping(Symbol name){
 	return mappings.get().valAt(name);
 }
 
+public void setMappings(IPersistentMap map) {
+    mappings.set(map);
+}
+
 public Var findInternedVar(Symbol symbol){
 	Object o = mappings.get().valAt(symbol);