Remove redundant locking in FeatureLoader

* The called methods already synchronize themselves.
* This could lead to deadlocks since TruffleRuby.synchronized uses a
  ReentrantLock and no longer the object's monitor.

Author: eregon

src/main/java/org/truffleruby/language/loader/FeatureLoader.java

@@ -20,7 +20,6 @@
 import java.util.Map;
 import java.util.concurrent.locks.ReentrantLock;
 
-import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
 import org.jcodings.Encoding;
 import org.jcodings.specific.UTF8Encoding;
 import org.truffleruby.RubyContext;
@@ -40,7 +39,6 @@
 import org.truffleruby.language.RubyConstant;
 import org.truffleruby.language.control.RaiseException;
 import org.truffleruby.language.dispatch.DispatchNode;
-import org.truffleruby.language.globals.GlobalVariables;
 import org.truffleruby.language.library.RubyStringLibrary;
 import org.truffleruby.platform.NativeConfiguration;
 import org.truffleruby.platform.Platform;
@@ -79,8 +77,6 @@ public class FeatureLoader {
     private NativeFunction getcwd;
     private static final int PATH_MAX = 1024; // jnr-posix hard codes this value
 
-    @CompilationFinal private RubyArray loadedFeatures = null;
-
     private static final String[] EXTENSIONS = new String[]{ TruffleRuby.EXTENSION, RubyLanguage.CEXT_EXTENSION };
 
     public FeatureLoader(RubyContext context, RubyLanguage language) {
@@ -491,13 +487,4 @@ public Object loadCExtLibrary(String feature, String path, Node currentNode) {
             Metrics.printTime("after-load-cext-" + feature);
         }
     }
-
-    public Object getLoadedFeaturesLock() {
-        if (loadedFeatures == null) {
-            CompilerDirectives.transferToInterpreterAndInvalidate();
-            GlobalVariables globals = context.getCoreLibrary().globalVariables;
-            loadedFeatures = (RubyArray) globals.getStorage("$LOADED_FEATURES").getValue();
-        }
-        return loadedFeatures;
-    }
 }

src/main/java/org/truffleruby/language/loader/RequireNode.java

@@ -388,18 +388,13 @@ private String getBaseName(String path) {
     }
 
     public boolean isFeatureLoaded(Object feature) {
-        final Object included;
-        synchronized (getContext().getFeatureLoader().getLoadedFeaturesLock()) {
-            included = isInLoadedFeatures
-                    .call(coreLibrary().truffleFeatureLoaderModule, "feature_provided?", feature, true);
-        }
+        final Object included = isInLoadedFeatures
+                .call(coreLibrary().truffleFeatureLoaderModule, "feature_provided?", feature, true);
         return booleanCastNode.executeToBoolean(included);
     }
 
     private void addToLoadedFeatures(Object feature) {
-        synchronized (getContext().getFeatureLoader().getLoadedFeaturesLock()) {
-            addToLoadedFeatures.call(coreLibrary().truffleFeatureLoaderModule, "provide_feature", feature);
-        }
+        addToLoadedFeatures.call(coreLibrary().truffleFeatureLoaderModule, "provide_feature", feature);
     }
 
     private void warnCircularRequire(String path) {