VolatileStruct, benchmark, and results

0001-Add-VolatileStruct-class.patch

From 6f4e6295ef0de1350cb9de423e85b3834a359c7d Mon Sep 17 00:00:00 2001
From: Charles Oliver Nutter <headius@headius.com>
Date: Thu, 6 Sep 2012 15:01:47 -0500
Subject: [PATCH] Add VolatileStruct class.

---
 src/org/jruby/RubyStruct.java         |  113 +++++----
 src/org/jruby/VolatileStruct.java     |  447 +++++++++++++++++++++++++++++++++
 src/org/jruby/runtime/ClassIndex.java |    3 +-
 3 files changed, 512 insertions(+), 51 deletions(-)
 create mode 100644 src/org/jruby/VolatileStruct.java

diff --git a/src/org/jruby/RubyStruct.java b/src/org/jruby/RubyStruct.java
index 869a4dd..6c323e0 100644
--- a/src/org/jruby/RubyStruct.java
+++ b/src/org/jruby/RubyStruct.java
@@ -54,8 +54,6 @@ import org.jruby.internal.runtime.methods.DynamicMethod;
 import org.jruby.javasupport.util.RuntimeHelpers;
 import org.jruby.runtime.ClassIndex;
 
-import java.util.concurrent.Callable;
-
 import static org.jruby.runtime.Visibility.*;
 
 import static org.jruby.javasupport.util.RuntimeHelpers.invokedynamic;
@@ -73,7 +71,7 @@ public class RubyStruct extends RubyObject {
      * @param runtime
      * @param rubyClass
      */
-    private RubyStruct(Ruby runtime, RubyClass rubyClass) {
+    protected RubyStruct(Ruby runtime, RubyClass rubyClass) {
         super(runtime, rubyClass);
         
         int size = RubyNumeric.fix2int(getInternalVariable((RubyClass)rubyClass, "__size__"));
@@ -90,6 +88,8 @@ public class RubyStruct extends RubyObject {
         structClass.includeModule(runtime.getEnumerable());
         structClass.defineAnnotatedMethods(RubyStruct.class);
 
+        VolatileStruct.createVolatileStructClass(runtime);
+
         return structClass;
     }
     
@@ -98,7 +98,7 @@ public class RubyStruct extends RubyObject {
         return ClassIndex.STRUCT;
     }
     
-    private static IRubyObject getInternalVariable(RubyClass type, String internedName) {
+    protected static IRubyObject getInternalVariable(RubyClass type, String internedName) {
         RubyClass structClass = type.getRuntime().getStructClass();
         IRubyObject variable;
 
@@ -113,11 +113,11 @@ public class RubyStruct extends RubyObject {
         return type.getRuntime().getNil();
     }
 
-    private RubyClass classOf() {
+    protected RubyClass classOf() {
         return getMetaClass() instanceof MetaClass ? getMetaClass().getSuperClass() : getMetaClass();
     }
 
-    private void modify() {
+    protected void modify() {
         testFrozen();
     }
     
@@ -224,6 +224,22 @@ public class RubyStruct extends RubyObject {
         newStruct.getSingletonClass().defineAnnotatedMethods(StructMethods.class);
 
         // define access methods.
+        defineAccessors(args, name, nilName, newStruct);
+
+        doYield(block, runtime, newStruct);
+
+        return newStruct;
+    }
+
+    protected static void doYield(Block block, Ruby runtime, RubyClass newStruct) {
+        if (block.isGiven()) {
+            // Struct bodies should be public by default, so set block visibility to public. JRUBY-1185.
+            block.getBinding().setVisibility(Visibility.PUBLIC);
+            block.yieldNonArray(runtime.getCurrentContext(), null, newStruct, newStruct);
+        }
+    }
+
+    protected static void defineAccessors(IRubyObject[] args, String name, boolean nilName, final RubyClass newStruct) {
         for (int i = (name == null && !nilName) ? 0 : 1; i < args.length; i++) {
             final String memberName = args[i].asJavaString();
             // if we are storing a name as well, index is one too high for values
@@ -249,12 +265,12 @@ public class RubyStruct extends RubyObject {
                 @Override
                 public IRubyObject call(ThreadContext context, IRubyObject self, RubyModule clazz, String name, IRubyObject[] args, Block block) {
                     Arity.checkArgumentCount(context.runtime, name, args, 1, 1);
-                    return ((RubyStruct)self).set(args[0], index);
+                    return ((RubyStruct)self).set(index, args[0]);
                 }
 
                 @Override
                 public IRubyObject call(ThreadContext context, IRubyObject self, RubyModule clazz, String name, IRubyObject arg) {
-                    return ((RubyStruct)self).set(arg, index);
+                    return ((RubyStruct)self).set(index, arg);
                 }
 
                 @Override
@@ -263,16 +279,8 @@ public class RubyStruct extends RubyObject {
                 }
             });
         }
-        
-        if (block.isGiven()) {
-            // Struct bodies should be public by default, so set block visibility to public. JRUBY-1185.
-            block.getBinding().setVisibility(Visibility.PUBLIC);
-            block.yieldNonArray(runtime.getCurrentContext(), null, newStruct, newStruct);
-        }
-
-        return newStruct;
     }
-    
+
     // For binding purposes on the newly created struct types
     public static class StructMethods {
         @JRubyMethod(name = {"new", "[]"}, rest = true)
@@ -356,9 +364,9 @@ public class RubyStruct extends RubyObject {
         return struct;
     }
 
-    private void checkSize(int length) {
-        if (length > values.length) {
-            throw getRuntime().newArgumentError("struct size differs (" + length +" for " + values.length + ")");
+    protected void checkSize(int length) {
+        if (length > length()) {
+            throw getRuntime().newArgumentError("struct size differs (" + length +" for " + length() + ")");
         }
     }
 
@@ -455,27 +463,32 @@ public class RubyStruct extends RubyObject {
     public RubyArray select(ThreadContext context, Block block) {
         RubyArray array = RubyArray.newArray(context.runtime);
         
-        for (int i = 0; i < values.length; i++) {
-            if (block.yield(context, values[i]).isTrue()) {
-                array.append(values[i]);
+        for (int i = 0; i < length(); i++) {
+            IRubyObject value = get(i);
+            if (block.yield(context, value).isTrue()) {
+                array.append(value);
             }
         }
         
         return array;
     }
 
-    public IRubyObject set(IRubyObject value, int index) {
+    protected IRubyObject set(int index, IRubyObject value) {
         modify();
 
         return values[index] = value;
     }
 
-    private RaiseException notStructMemberError(String name) {
-        return getRuntime().newNameError(name + " is not struct member", name);
+    protected IRubyObject get(int index) {
+        return values[index];
     }
 
-    public IRubyObject get(int index) {
-        return values[index];
+    protected int length() {
+        return values.length;
+    }
+
+    protected RaiseException notStructMemberError(String name) {
+        return getRuntime().newNameError(name + " is not struct member", name);
     }
 
     @Override
@@ -502,8 +515,8 @@ public class RubyStruct extends RubyObject {
                 if (recur) {
                     return runtime.getTrue();
                 }
-                for (int i = 0; i < values.length; i++) {
-                    if (!equalInternal(context, values[i], otherStruct.values[i])) return runtime.getFalse();
+                for (int i = 0; i < length(); i++) {
+                    if (!equalInternal(context, get(i), otherStruct.get(i))) return runtime.getFalse();
                 }
                 return runtime.getTrue();
             }
@@ -528,8 +541,8 @@ public class RubyStruct extends RubyObject {
                 if (recur) {
                     return runtime.getTrue();
                 }
-                for (int i = 0; i < values.length; i++) {
-                    if (!eqlInternal(context, values[i], otherStruct.values[i])) return runtime.getFalse();
+                for (int i = 0; i < length(); i++) {
+                    if (!eqlInternal(context, get(i), otherStruct.get(i))) return runtime.getFalse();
                 }
                 return runtime.getTrue();
             }
@@ -553,7 +566,7 @@ public class RubyStruct extends RubyObject {
             // FIXME: MRI has special case for constants here 
             buffer.append(RubyString.objAsString(context, member.eltInternal(i)).getByteList());
             buffer.append('=');
-            buffer.append(inspect(context, values[i]).getByteList());
+            buffer.append(inspect(context, get(i)).getByteList());
         }
 
         buffer.append('>');
@@ -579,12 +592,12 @@ public class RubyStruct extends RubyObject {
 
     @JRubyMethod(name = {"size", "length"} )
     public RubyFixnum size() {
-        return getRuntime().newFixnum(values.length);
+        return getRuntime().newFixnum(length());
     }
 
     public IRubyObject eachInternal(ThreadContext context, Block block) {
-        for (int i = 0; i < values.length; i++) {
-            block.yield(context, values[i]);
+        for (int i = 0; i < length(); i++) {
+            block.yield(context, get(i));
         }
 
         return this;
@@ -600,8 +613,8 @@ public class RubyStruct extends RubyObject {
 
         assert !member.isNil() : "uninitialized struct";
 
-        for (int i = 0; i < values.length; i++) {
-            block.yield(context, getRuntime().newArrayNoCopy(new IRubyObject[]{member.eltInternal(i), values[i]}));
+        for (int i = 0; i < length(); i++) {
+            block.yield(context, getRuntime().newArrayNoCopy(new IRubyObject[]{member.eltInternal(i), get(i)}));
         }
 
         return this;
@@ -620,15 +633,15 @@ public class RubyStruct extends RubyObject {
 
         int idx = RubyNumeric.fix2int(key);
 
-        idx = idx < 0 ? values.length + idx : idx;
+        idx = idx < 0 ? length() + idx : idx;
 
         if (idx < 0) {
-            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + values.length + ")");
-        } else if (idx >= values.length) {
-            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + values.length + ")");
+            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + length() + ")");
+        } else if (idx >= length()) {
+            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + length() + ")");
         }
 
-        return values[idx];
+        return get(idx);
     }
 
     @JRubyMethod(name = "[]=", required = 2)
@@ -639,16 +652,16 @@ public class RubyStruct extends RubyObject {
 
         int idx = RubyNumeric.fix2int(key);
 
-        idx = idx < 0 ? values.length + idx : idx;
+        idx = idx < 0 ? length() + idx : idx;
 
         if (idx < 0) {
-            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + values.length + ")");
-        } else if (idx >= values.length) {
-            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + values.length + ")");
+            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + length() + ")");
+        } else if (idx >= length()) {
+            throw getRuntime().newIndexError("offset " + idx + " too large for struct (size:" + length() + ")");
         }
 
         modify();
-        return values[idx] = value;
+        return set(idx, value);
     }
     
     // FIXME: This is copied code from RubyArray.  Both RE, Struct, and Array should share one impl
@@ -656,7 +669,7 @@ public class RubyStruct extends RubyObject {
     // of something lower.
     @JRubyMethod(rest = true)
     public IRubyObject values_at(IRubyObject[] args) {
-        int olen = values.length;
+        int olen = length();
         RubyArray result = getRuntime().newArray(args.length);
 
         for (int i = 0; i < args.length; i++) {
@@ -694,7 +707,7 @@ public class RubyStruct extends RubyObject {
         for (int i = 0; i < array.size(); i++) {
             RubySymbol name = (RubySymbol) array.eltInternal(i);
             output.dumpObject(name);
-            output.dumpObject(struct.values[i]);
+            output.dumpObject(struct.get(i));
         }
     }
 
diff --git a/src/org/jruby/VolatileStruct.java b/src/org/jruby/VolatileStruct.java
new file mode 100644
index 0000000..203575a
--- /dev/null
+++ b/src/org/jruby/VolatileStruct.java
@@ -0,0 +1,447 @@
+/***** BEGIN LICENSE BLOCK *****
+ * Version: CPL 1.0/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Common Public
+ * License Version 1.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.eclipse.org/legal/cpl-v10.html
+ *
+ * Software distributed under the License is distributed on an "AS
+ * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
+ * implied. See the License for the specific language governing
+ * rights and limitations under the License.
+ *
+ * Copyright (C) 2002 Benoit Cerrina <b.cerrina@wanadoo.fr>
+ * Copyright (C) 2002-2004 Anders Bengtsson <ndrsbngtssn@yahoo.se>
+ * Copyright (C) 2002-2004 Jan Arne Petersen <jpetersen@uni-bonn.de>
+ * Copyright (C) 2004 Thomas E Enebo <enebo@acm.org>
+ * Copyright (C) 2004 Stefan Matthias Aust <sma@3plus4.de>
+ * Copyright (C) 2005 Charles O Nutter <headius@headius.com>
+ * 
+ * Alternatively, the contents of this file may be used under the terms of
+ * either of the GNU General Public License Version 2 or later (the "GPL"),
+ * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the CPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the CPL, the GPL or the LGPL.
+ ***** END LICENSE BLOCK *****/
+package org.jruby;
+
+import org.jruby.anno.JRubyClass;
+import org.jruby.anno.JRubyMethod;
+import org.jruby.common.IRubyWarnings.ID;
+import org.jruby.internal.runtime.methods.CallConfiguration;
+import org.jruby.internal.runtime.methods.DynamicMethod;
+import org.jruby.javasupport.util.RuntimeHelpers;
+import org.jruby.runtime.Arity;
+import org.jruby.runtime.Block;
+import org.jruby.runtime.ClassIndex;
+import org.jruby.runtime.ObjectAllocator;
+import org.jruby.runtime.ThreadContext;
+import org.jruby.runtime.Visibility;
+import org.jruby.runtime.builtin.IRubyObject;
+import org.jruby.util.IdUtil;
+
+import java.util.Arrays;
+import java.util.concurrent.atomic.AtomicReferenceArray;
+
+import static org.jruby.javasupport.util.RuntimeHelpers.invokedynamic;
+import static org.jruby.runtime.MethodIndex.HASH;
+
+/**
+ * @author  jpetersen
+ */
+@JRubyClass(name="Volatile")
+public class VolatileStruct extends RubyStruct {
+    private final AtomicReferenceArray<IRubyObject> values;
+
+    /**
+     * Constructor for VolatileStruct.
+     * @param runtime
+     * @param rubyClass
+     */
+    private VolatileStruct(Ruby runtime, RubyClass rubyClass) {
+        super(runtime, rubyClass);
+        
+        int size = RubyNumeric.fix2int(getInternalVariable((RubyClass)rubyClass, "__size__"));
+
+        IRubyObject[] nils = runtime.getNilPrefilledArray();
+        if (size <= nils.length) {
+            values = new AtomicReferenceArray<IRubyObject>(Arrays.copyOf(runtime.getNilPrefilledArray(), size));
+        } else {
+            IRubyObject[] tmp = new IRubyObject[size];
+            RuntimeHelpers.fillNil(tmp, runtime);
+            values = new AtomicReferenceArray<IRubyObject>(tmp);
+        }
+    }
+
+    public static RubyClass createVolatileStructClass(Ruby runtime) {
+        RubyClass volatileStructClass = runtime.defineClass("VolatileStruct", runtime.getStructClass(), ObjectAllocator.NOT_ALLOCATABLE_ALLOCATOR);
+        volatileStructClass.index = ClassIndex.VOLATILE_STRUCT;
+        volatileStructClass.includeModule(runtime.getEnumerable());
+        volatileStructClass.defineAnnotatedMethods(VolatileStruct.class);
+
+        return volatileStructClass;
+    }
+    
+    @Override
+    public int getNativeTypeIndex() {
+        return ClassIndex.VOLATILE_STRUCT;
+    }
+    
+    @Override
+    public RubyFixnum hash(ThreadContext context) {
+        Ruby runtime = getRuntime();
+        int h = getMetaClass().getRealClass().hashCode();
+
+        for (int i = 0; i < values.length(); i++) {
+            h = (h << 1) | (h < 0 ? 1 : 0);
+            h ^= RubyNumeric.num2long(invokedynamic(context, values.get(i), HASH));
+        }
+        
+        return runtime.newFixnum(h);
+    }
+
+    // Struct methods
+
+    /** Create new Struct class.
+     *
+     * MRI: rb_struct_s_def / make_struct
+     *
+     */
+    @JRubyMethod(name = "new", required = 1, rest = true, meta = true)
+    public static RubyClass newInstance(IRubyObject recv, IRubyObject[] args, Block block) {
+        String name = null;
+        boolean nilName = false;
+        Ruby runtime = recv.getRuntime();
+
+        if (args.length > 0) {
+            IRubyObject firstArgAsString = args[0].checkStringType();
+            if (!firstArgAsString.isNil()) {
+                name = ((RubyString)firstArgAsString).getByteList().toString();
+            } else if (args[0].isNil()) {
+                nilName = true;
+            }
+        }
+
+        RubyArray member = runtime.newArray();
+
+        for (int i = (name == null && !nilName) ? 0 : 1; i < args.length; i++) {
+            member.append(runtime.newSymbol(args[i].asJavaString()));
+        }
+
+        RubyClass newStruct;
+        RubyClass superClass = (RubyClass)recv;
+
+        if (name == null || nilName) {
+            newStruct = RubyClass.newClass(runtime, superClass);
+            newStruct.setAllocator(VOLATILE_STRUCT_INSTANCE_ALLOCATOR);
+            newStruct.makeMetaClass(superClass.getMetaClass());
+            newStruct.inherit(superClass);
+        } else {
+            if (!IdUtil.isConstant(name)) {
+                throw runtime.newNameError("identifier " + name + " needs to be constant", name);
+            }
+
+            IRubyObject type = superClass.getConstantAt(name);
+            if (type != null) {
+                ThreadContext context = runtime.getCurrentContext();
+                runtime.getWarnings().warn(ID.STRUCT_CONSTANT_REDEFINED, context.getFile(), context.getLine(), "redefining constant Struct::" + name);
+                superClass.remove_const(context, runtime.newString(name));
+            }
+            newStruct = superClass.defineClassUnder(name, superClass, VOLATILE_STRUCT_INSTANCE_ALLOCATOR);
+        }
+
+        // set reified class to VolatileStruct, for Java subclasses to use
+        newStruct.setReifiedClass(VolatileStruct.class);
+        newStruct.index = ClassIndex.STRUCT;
+        
+        newStruct.setInternalVariable("__size__", member.length());
+        newStruct.setInternalVariable("__member__", member);
+
+        newStruct.getSingletonClass().defineAnnotatedMethods(VolatileStructMethods.class);
+
+        // define access methods.
+        defineAccessors(args, name, nilName, newStruct);
+        defineAtomicAccessors(args, name, nilName, newStruct);
+
+        doYield(block, runtime, newStruct);
+
+        return newStruct;
+    }
+
+    protected static void defineAtomicAccessors(IRubyObject[] args, String name, boolean nilName, final RubyClass newStruct) {
+        for (int i = (name == null && !nilName) ? 0 : 1; i < args.length; i++) {
+            final String memberName = args[i].asJavaString();
+            // if we are storing a name as well, index is one too high for values
+            final int index = (name == null && !nilName) ? i : i - 1;
+            newStruct.addMethod("swap_" + memberName, new DynamicMethod(newStruct, Visibility.PUBLIC, CallConfiguration.FrameNoneScopeNone) {
+                @Override
+                public IRubyObject call(ThreadContext context, IRubyObject self, RubyModule clazz, String name, IRubyObject[] args, Block block) {
+                    Arity.checkArgumentCount(context.runtime, name, args, 1, 1);
+                    return ((VolatileStruct)self).values.getAndSet(index, args[0]);
+                }
+
+                @Override
+                public IRubyObject call(ThreadContext context, IRubyObject self, RubyModule clazz, String name, IRubyObject arg0) {
+                    return ((VolatileStruct)self).values.getAndSet(index, arg0);
+                }
+
+                @Override
+                public DynamicMethod dup() {
+                    return this;
+                }
+            });
+            newStruct.addMethod("cas_" + memberName, new DynamicMethod(newStruct, Visibility.PUBLIC, CallConfiguration.FrameNoneScopeNone) {
+                @Override
+                public IRubyObject call(ThreadContext context, IRubyObject self, RubyModule clazz, String name, IRubyObject[] args, Block block) {
+                    Arity.checkArgumentCount(context.runtime, name, args, 2, 2);
+                    return context.runtime.newBoolean(
+                            ((VolatileStruct)self).values.compareAndSet(index, args[0], args[1]));
+                }
+
+                @Override
+                public IRubyObject call(ThreadContext context, IRubyObject self, RubyModule clazz, String name, IRubyObject arg0, IRubyObject arg1) {
+                    return context.runtime.newBoolean(
+                            ((VolatileStruct)self).values.compareAndSet(index, arg0, arg1));
+                }
+
+                @Override
+                public DynamicMethod dup() {
+                    return this;
+                }
+            });
+        }
+    }
+
+    // For binding purposes on the newly created struct types
+    public static class VolatileStructMethods {
+        @JRubyMethod(name = {"new", "[]"}, rest = true)
+        public static IRubyObject newStruct(IRubyObject recv, IRubyObject[] args, Block block) {
+            return VolatileStruct.newStruct(recv, args, block);
+        }
+
+        @JRubyMethod(name = {"new", "[]"})
+        public static IRubyObject newStruct(IRubyObject recv, Block block) {
+            return VolatileStruct.newStruct(recv, block);
+        }
+
+        @JRubyMethod(name = {"new", "[]"})
+        public static IRubyObject newStruct(IRubyObject recv, IRubyObject arg0, Block block) {
+            return VolatileStruct.newStruct(recv, arg0, block);
+        }
+
+        @JRubyMethod(name = {"new", "[]"})
+        public static IRubyObject newStruct(IRubyObject recv, IRubyObject arg0, IRubyObject arg1, Block block) {
+            return VolatileStruct.newStruct(recv, arg0, arg1, block);
+        }
+
+        @JRubyMethod(name = {"new", "[]"})
+        public static IRubyObject newStruct(IRubyObject recv, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2, Block block) {
+            return VolatileStruct.newStruct(recv, arg0, arg1, arg2, block);
+        }
+
+        @JRubyMethod(name = "members", compat = CompatVersion.RUBY1_8)
+        public static IRubyObject members(IRubyObject recv, Block block) {
+            return VolatileStruct.members(recv, block);
+        }
+
+        @JRubyMethod(name = "members", compat = CompatVersion.RUBY1_9)
+        public static IRubyObject members19(IRubyObject recv, Block block) {
+            return VolatileStruct.members19(recv, block);
+        }
+    }
+
+    /** Create new Structure.
+     *
+     * MRI: struct_alloc
+     *
+     */
+    public static VolatileStruct newStruct(IRubyObject recv, IRubyObject[] args, Block block) {
+        VolatileStruct struct = new VolatileStruct(recv.getRuntime(), (RubyClass) recv);
+
+        struct.callInit(args, block);
+
+        return struct;
+    }
+
+    public static VolatileStruct newStruct(IRubyObject recv, Block block) {
+        VolatileStruct struct = new VolatileStruct(recv.getRuntime(), (RubyClass) recv);
+
+        struct.callInit(block);
+
+        return struct;
+    }
+
+    public static VolatileStruct newStruct(IRubyObject recv, IRubyObject arg0, Block block) {
+        VolatileStruct struct = new VolatileStruct(recv.getRuntime(), (RubyClass) recv);
+
+        struct.callInit(arg0, block);
+
+        return struct;
+    }
+
+    public static VolatileStruct newStruct(IRubyObject recv, IRubyObject arg0, IRubyObject arg1, Block block) {
+        VolatileStruct struct = new VolatileStruct(recv.getRuntime(), (RubyClass) recv);
+
+        struct.callInit(arg0, arg1, block);
+
+        return struct;
+    }
+
+    public static VolatileStruct newStruct(IRubyObject recv, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2, Block block) {
+        VolatileStruct struct = new VolatileStruct(recv.getRuntime(), (RubyClass) recv);
+
+        struct.callInit(arg0, arg1, arg2, block);
+
+        return struct;
+    }
+
+    @Override
+    public IRubyObject initialize(ThreadContext context, IRubyObject[] args) {
+        modify();
+        checkSize(args.length);
+
+        IRubyObject nil = context.nil;
+
+        int i = 0;
+        for (; i < args.length; i++) {
+            values.set(i, args[i]);
+        }
+        for (; i < values.length(); i++) {
+            values.set(i, nil);
+        }
+
+        return nil;
+    }
+
+    @Override
+    public IRubyObject initialize(ThreadContext context) {
+        IRubyObject nil = context.nil;
+        return initializeInternal(context, 0, nil, nil, nil);
+    }
+
+    @Override
+    public IRubyObject initialize(ThreadContext context, IRubyObject arg0) {
+        IRubyObject nil = context.nil;
+        return initializeInternal(context, 1, arg0, nil, nil);
+    }
+
+    @Override
+    public IRubyObject initialize(ThreadContext context, IRubyObject arg0, IRubyObject arg1) {
+        return initializeInternal(context, 2, arg0, arg1, context.nil);
+    }
+
+    @Override
+    public IRubyObject initialize(ThreadContext context, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2) {
+        return initializeInternal(context, 3, arg0, arg1, arg2);
+    }
+
+    @Override
+    public IRubyObject initializeInternal(ThreadContext context, int provided, IRubyObject arg0, IRubyObject arg1, IRubyObject arg2) {
+        modify();
+        checkSize(provided);
+
+        switch (provided) {
+        case 3:
+            values.set(2, arg2);
+        case 2:
+            values.set(1, arg1);
+        case 1:
+            values.set(0, arg0);
+        }
+
+        IRubyObject nil = context.nil;
+
+        for (; provided < values.length(); provided++) {
+            values.set(provided, nil);
+        }
+
+        return nil;
+    }
+    
+    public static RubyArray members(IRubyObject recv, Block block) {
+        RubyArray member = (RubyArray) getInternalVariable((RubyClass) recv, "__member__");
+
+        assert !member.isNil() : "uninitialized struct";
+
+        RubyArray result = recv.getRuntime().newArray(member.getLength());
+        for (int i = 0,k=member.getLength(); i < k; i++) {
+            // this looks weird, but it's because they're RubySymbol and that's java.lang.String internally
+            result.append(recv.getRuntime().newString(member.eltInternal(i).asJavaString()));
+        }
+
+        return result;
+    }
+
+    public static RubyArray members19(IRubyObject recv, Block block) {
+        RubyArray member = (RubyArray) getInternalVariable((RubyClass) recv, "__member__");
+
+        assert !member.isNil() : "uninitialized struct";
+
+        RubyArray result = recv.getRuntime().newArray(member.getLength());
+        for (int i = 0,k=member.getLength(); i < k; i++) {
+            result.append(member.eltInternal(i));
+        }
+
+        return result;
+    }
+
+    @Override
+    public RubyArray members() {
+        return members(classOf(), Block.NULL_BLOCK);
+    }
+
+    @Override
+    public RubyArray members19() {
+        return members19(classOf(), Block.NULL_BLOCK);
+    }
+
+    protected IRubyObject set(int index, IRubyObject value) {
+        modify();
+
+        values.set(index, value);
+
+        return value;
+    }
+
+    protected IRubyObject get(int index) {
+        return values.get(index);
+    }
+
+    protected int length() {
+        return values.length();
+    }
+
+    @Override
+    public void copySpecialInstanceVariables(IRubyObject clone) {
+        VolatileStruct struct = (VolatileStruct)clone;
+        for (int i = 0; i < length(); i++) {
+            struct.set(i, get(i));
+        }
+    }
+
+    @Override
+    public RubyArray to_a() {
+        IRubyObject[] ary = new IRubyObject[values.length()];
+
+        for (int i = 0; i < values.length(); i++) ary[i] = values.get(i);
+
+        return getRuntime().newArray(ary);
+    }
+    
+    private static ObjectAllocator VOLATILE_STRUCT_INSTANCE_ALLOCATOR = new ObjectAllocator() {
+        public IRubyObject allocate(Ruby runtime, RubyClass klass) {
+            VolatileStruct instance = new VolatileStruct(runtime, klass);
+            
+            instance.setMetaClass(klass);
+            
+            return instance;
+        }
+    };
+}
diff --git a/src/org/jruby/runtime/ClassIndex.java b/src/org/jruby/runtime/ClassIndex.java
index bb77739..00a0291 100644
--- a/src/org/jruby/runtime/ClassIndex.java
+++ b/src/org/jruby/runtime/ClassIndex.java
@@ -54,7 +54,8 @@ public final class ClassIndex {
     public static final int UNBOUNDMETHOD = 36;
     public static final int CONTINUATION = 37;
     public static final int BASICOBJECT = 38;
-    public static final int MAX_CLASSES = 39;
+    public static final int VOLATILE_STRUCT = 39;
+    public static final int MAX_CLASSES = 40;
 
     /** Creates a new instance of ClassIndex */
     private ClassIndex() {
-- 
1.7.10.4

bench_struct.rb

require 'benchmark/ips'

HAVE_VSTRUCT = defined?(VolatileStruct)

Foo = Struct.new(:a, :b, :c, :d, :e)
Bar = VolatileStruct.new(:a, :b, :c, :d, :e) if HAVE_VSTRUCT

Benchmark.ips do |bm|
  foo = Foo.new(1, 2, 3, 4, 5)
  bar = Bar.new(1, 2, 3, 4, 5) if HAVE_VSTRUCT

  bm.report("struct member access") {|n|
    n.times { foo.a; foo.b; foo.c; foo.d; foo.e }
  }
  bm.report("struct member mutate") {|n|
    n.times { foo.a=1; foo.b=1; foo.c=1; foo.d=1; foo.e=1 }
  }
  bm.report("struct to_s") {|n|
    n.times { foo.to_s }
  }
  bm.report("struct each") {|n|
    n.times { foo.each {|x| x} }
  }
  bm.report("struct allocation") {|n|
    n.times { Foo.new(1, 2, 3, 4, 5) }
  }
  next unless HAVE_VSTRUCT
  bm.report("vstruct member access") {|n|
    n.times { bar.a; bar.b; bar.c; bar.d; bar.e }
  }
  bm.report("vstruct member mutate") {|n|
    n.times { bar.a=1; bar.b=2; bar.c=3; bar.d=4; bar.e=5 }
  }
  bm.report("vstruct to_s") {|n|
    n.times { bar.to_s }
  }
  bm.report("vstruct each") {|n|
    n.times { bar.each {|x| x} }
  }
  bm.report("vstruct allocation") {|n|
    n.times { Bar.new(1, 2, 3, 4, 5) }
  }
  bm.report("vstruct swap") {|n|
    n.times { bar.swap_a(1); bar.swap_b(2); bar.swap_c(3); bar.swap_d(4); bar.swap_e(5) }
  }
  bm.report("vstruct cas") {|n|
    n.times { bar.cas_a(1,1); bar.cas_b(2,2); bar.cas_c(3,3); bar.cas_d(4,4); bar.cas_e(5,5) }
  }
end

results

Ruby 1.9.3

struct member access  2704659.5 (±1.8%) i/s -   13523244 in   5.001728s
struct member mutate  1392143.5 (±2.2%) i/s -    6984750 in   5.019915s
         struct to_s   310352.7 (±1.4%) i/s -    1566728 in   5.049164s
         struct each  2069069.9 (±2.4%) i/s -   10388650 in   5.024132s
   struct allocation  1940827.3 (±8.2%) i/s -    9642576 in   5.003262s

JRuby

struct member access  8876567.2 (±5.5%) i/s -   44150546 in   4.992000s
struct member mutate  7959387.2 (±5.1%) i/s -   39744642 in   5.008000s
         struct to_s   863746.5 (±2.5%) i/s -    4348708 in   5.038000s
         struct each  2827729.3 (±3.0%) i/s -   14165010 in   5.014000s
   struct allocation  6065116.7 (±4.9%) i/s -   30225746 in   4.997000s
vstruct member access
                      7535692.1 (±4.8%) i/s -   37605387 in   5.003000s
vstruct member mutate
                      5455515.1 (±4.4%) i/s -   27215706 in   4.999000s
        vstruct to_s   849120.5 (±2.6%) i/s -    4279102 in   5.043000s
        vstruct each  2796831.4 (±3.8%) i/s -   13979980 in   5.007000s
  vstruct allocation  3227549.3 (±4.6%) i/s -   16135345 in   5.014000s
        vstruct swap  6802820.6 (±4.8%) i/s -   33909096 in   4.997000s
         vstruct cas  7096547.3 (±4.4%) i/s -   35355473 in   4.993000s