Implement loaded feature caching to reduce load path searching.

src/org/jruby/RubyArray.java

@@ -416,8 +416,8 @@ public IRubyObject[] toJavaArrayUnsafe() {
 
     public IRubyObject[] toJavaArrayMaybeUnsafe() {
         return (!isShared && begin == 0 && values.length == realLength) ? values : toJavaArray();
-    }    
-
+    }
+    
     /** rb_ary_make_shared
     *
     */

src/org/jruby/runtime/load/LoadService.java

@@ -43,10 +43,12 @@
 import java.net.URI;
 import java.net.URL;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.jar.JarFile;
@@ -204,6 +206,8 @@ public String[] getSuffixes() {
 
     protected RubyArray loadPath;
     protected StringArraySet loadedFeatures;
+    protected RubyArray loadedFeaturesDup;
+    private final Map<String, String> loadedFeaturesIndex = new ConcurrentHashMap<String, String>();
     protected final Map<String, Library> builtinLibraries = new HashMap<String, Library>();
 
     protected final Map<String, JarFile> jarFiles = new HashMap<String, JarFile>();
@@ -296,9 +300,20 @@ public void addPaths(String... additionalDirectories) {
             addPath(dir);
         }
     }
+
+    protected boolean isFeatureInIndex(String shortName) {
+        return loadedFeaturesIndex.containsKey(shortName);
+    }
 
-    protected void addLoadedFeature(String name) {
+    protected void addLoadedFeature(String shortName, String name) {
         loadedFeatures.append(RubyString.newString(runtime, name));
+
+        addFeatureToIndex(shortName, name);
+    }
+
+    protected void addFeatureToIndex(String shortName, String name) {
+        loadedFeaturesDup = (RubyArray)loadedFeatures.dup();
+        loadedFeaturesIndex.put(shortName, name);
     }
 
     protected void addPath(String path) {
@@ -536,7 +551,7 @@ private boolean smartLoadInternal(String file) {
 
         boolean loaded = tryLoadingLibraryOrScript(runtime, state);
         if (loaded) {
-            addLoadedFeature(state.loadName);
+            addLoadedFeature(file, state.loadName);
         }
         return loaded;
     }
@@ -627,9 +642,27 @@ public void removeInternalLoadedFeature(String name) {
         RubyString nameRubyString = runtime.newString(name);
         loadedFeatures.delete(runtime.getCurrentContext(), nameRubyString, Block.NULL_BLOCK);
     }
+
+    private boolean isFeaturesIndexUpToDate() {
+        // disable tracing during index check
+        runtime.getCurrentContext().preTrace();
+        try {
+            return loadedFeaturesDup != null && loadedFeaturesDup.eql(loadedFeatures);
+        } finally {
+            runtime.getCurrentContext().postTrace();
+        }
+    }
 
     protected boolean featureAlreadyLoaded(String name) {
-        return loadedFeatures.containsString(name);
+        if (loadedFeatures.containsString(name)) return true;
+
+        // Bail if our features index fell out of date.
+        if (!isFeaturesIndexUpToDate()) { 
+            loadedFeaturesIndex.clear();
+            return false;
+        }
+
+        return isFeatureInIndex(name);
     }
 
     protected boolean isJarfileLibrary(SearchState state, final String file) {