diff --git a/classpath/java-lang.cpp b/classpath/java-lang.cpp
index 5fd06cc8fe..8825b8ffa3 100644
--- a/classpath/java-lang.cpp
+++ b/classpath/java-lang.cpp
@@ -267,7 +267,7 @@ Java_java_lang_Runtime_exec(JNIEnv* e, jclass,
     
     // Error if here
     char c = errno;
-    write(msg[1], &c, 1);
+    ssize_t rv UNUSED = write(msg[1], &c, 1);
     exit(127);
   } break;
     
diff --git a/classpath/java-nio.cpp b/classpath/java-nio.cpp
index 86eb9aa6c5..e5a0e345ff 100644
--- a/classpath/java-nio.cpp
+++ b/classpath/java-nio.cpp
@@ -26,6 +26,7 @@
 #  include <errno.h>
 #  include <netdb.h>
 #  include <sys/select.h>
+#  include <netinet/tcp.h>
 #endif
 
 #define java_nio_channels_SelectionKey_OP_READ 1L
@@ -88,6 +89,26 @@ throwIOException(JNIEnv* e)
   throwIOException(e, errorString(e));
 }
 
+void
+throwSocketException(JNIEnv* e, const char* s)
+{
+  throwNew(e, "java/net/SocketException", s);
+}
+
+void
+throwSocketException(JNIEnv* e, jbyteArray a)
+{
+  jbyte* s = static_cast<jbyte*>(e->GetPrimitiveArrayCritical(a, 0));
+  throwSocketException(e, reinterpret_cast<const char*>(s));
+  e->ReleasePrimitiveArrayCritical(a, s, 0);
+}
+
+void
+throwSocketException(JNIEnv* e)
+{
+  throwSocketException(e, errorString(e));
+}
+
 void
 init(JNIEnv* e, sockaddr_in* address, jstring hostString, jint port)
 {
@@ -152,6 +173,19 @@ makeNonblocking(JNIEnv* e, int d)
   return true;
 }
 
+bool
+setTcpNoDelay(JNIEnv* e, int d, bool on)
+{
+  int flag = on;
+  int r = setsockopt
+    (d, IPPROTO_TCP, TCP_NODELAY, reinterpret_cast<char*>(&flag), sizeof(int));
+  if (r < 0) {
+    throwSocketException(e);
+    return false;
+  }
+  return true;
+}
+
 void
 doListen(JNIEnv* e, int s, sockaddr_in* address)
 {
@@ -277,6 +311,15 @@ Java_java_nio_channels_ServerSocketChannel_natDoListen(JNIEnv *e,
   return s;
 }
 
+extern "C" JNIEXPORT void JNICALL
+Java_java_nio_channels_SocketChannel_natSetTcpNoDelay(JNIEnv *e,
+                                                      jclass,
+                                                      jint socket,
+                                                      jboolean on)
+{
+  setTcpNoDelay(e, socket, on);
+}
+
 extern "C" JNIEXPORT jint JNICALL
 Java_java_nio_channels_SocketChannel_natDoConnect(JNIEnv *e,
 						  jclass,
diff --git a/classpath/java/net/Socket.java b/classpath/java/net/Socket.java
new file mode 100644
index 0000000000..602b24a19e
--- /dev/null
+++ b/classpath/java/net/Socket.java
@@ -0,0 +1,15 @@
+/* Copyright (c) 2008, Avian Contributors
+
+   Permission to use, copy, modify, and/or distribute this software
+   for any purpose with or without fee is hereby granted, provided
+   that the above copyright notice and this permission notice appear
+   in all copies.
+
+   There is NO WARRANTY for this software.  See license.txt for
+   details. */
+
+package java.net;
+
+public abstract class Socket {
+  public abstract void setTcpNoDelay(boolean on) throws SocketException;
+}
diff --git a/classpath/java/net/SocketException.java b/classpath/java/net/SocketException.java
new file mode 100644
index 0000000000..f0a9ee2ac3
--- /dev/null
+++ b/classpath/java/net/SocketException.java
@@ -0,0 +1,23 @@
+/* Copyright (c) 2008, Avian Contributors
+
+   Permission to use, copy, modify, and/or distribute this software
+   for any purpose with or without fee is hereby granted, provided
+   that the above copyright notice and this permission notice appear
+   in all copies.
+
+   There is NO WARRANTY for this software.  See license.txt for
+   details. */
+
+package java.net;
+
+import java.io.IOException;
+
+public class SocketException extends IOException {
+  public SocketException(String message) {
+    super(message);
+  }
+
+  public SocketException() {
+    this(null);
+  }
+}
diff --git a/classpath/java/nio/channels/ServerSocketChannel.java b/classpath/java/nio/channels/ServerSocketChannel.java
index c1311b5116..f84c9626bc 100644
--- a/classpath/java/nio/channels/ServerSocketChannel.java
+++ b/classpath/java/nio/channels/ServerSocketChannel.java
@@ -16,11 +16,21 @@ import java.net.InetSocketAddress;
 import java.net.SocketAddress;
 import java.net.ServerSocket;
 
-public class ServerSocketChannel extends SocketChannel {
+public class ServerSocketChannel extends SelectableChannel {
+  private final SocketChannel channel = new SocketChannel();
+
   public static ServerSocketChannel open() {
     return new ServerSocketChannel();
   }
 
+  public SelectableChannel configureBlocking(boolean v) {
+    return channel.configureBlocking(v);
+  }
+
+  public void close() throws IOException {
+    channel.close();
+  }
+
   public SocketChannel accept() throws Exception {
     SocketChannel c = new SocketChannel();
     c.socket = doAccept();
@@ -33,7 +43,7 @@ public class ServerSocketChannel extends SocketChannel {
   }
 
   private int doAccept() throws IOException {
-    return natDoAccept(socket);
+    return natDoAccept(channel.socket);
   }
 
   private int doListen(String host, int port) throws IOException {
@@ -50,7 +60,7 @@ public class ServerSocketChannel extends SocketChannel {
       } catch (ClassCastException e) {
         throw new IllegalArgumentException();
       }
-      socket = doListen(a.getHostName(), a.getPort());
+      channel.socket = doListen(a.getHostName(), a.getPort());
     }
   }
 
diff --git a/classpath/java/nio/channels/SocketChannel.java b/classpath/java/nio/channels/SocketChannel.java
index cc4b2abb90..aa723030db 100644
--- a/classpath/java/nio/channels/SocketChannel.java
+++ b/classpath/java/nio/channels/SocketChannel.java
@@ -11,8 +11,10 @@
 package java.nio.channels;
 
 import java.io.IOException;
+import java.net.SocketException;
 import java.net.SocketAddress;
 import java.net.InetSocketAddress;
+import java.net.Socket;
 import java.nio.ByteBuffer;
 
 public class SocketChannel extends SelectableChannel
@@ -20,8 +22,8 @@ public class SocketChannel extends SelectableChannel
 {
   public static final int InvalidSocket = -1;
 
-  protected int socket = InvalidSocket;
-  protected boolean connected = false;
+  int socket = InvalidSocket;
+  boolean connected = false;
 
   public static SocketChannel open() {
     return new SocketChannel();
@@ -32,6 +34,10 @@ public class SocketChannel extends SelectableChannel
     return this;
   }
 
+  public Socket socket() {
+    return new Handle();
+  }
+
   public boolean connect(SocketAddress address) throws Exception {
     InetSocketAddress a;
     try {
@@ -87,6 +93,15 @@ public class SocketChannel extends SelectableChannel
     return socket;
   }
 
+  public class Handle extends Socket {
+    public void setTcpNoDelay(boolean on) throws SocketException {
+      natSetTcpNoDelay(socket, on);
+    }
+  }
+
+  private static native void natSetTcpNoDelay(int socket, boolean on)
+    throws SocketException;
+
   private static native int natDoConnect(String host, int port, boolean[] connected)
     throws Exception;
   private static native int natRead(int socket, byte[] buffer, int offset, int length)
diff --git a/makefile b/makefile
index eab488d091..90ea95aecb 100644
--- a/makefile
+++ b/makefile
@@ -59,7 +59,7 @@ rdynamic = -rdynamic
 warnings = -Wall -Wextra -Werror -Wunused-parameter -Winit-self \
 	-Wno-non-virtual-dtor
 
-common-cflags = $(warnings) -fno-rtti -fno-exceptions \
+common-cflags = $(warnings) -fno-rtti -fno-exceptions -fno-omit-frame-pointer \
 	"-I$(JAVA_HOME)/include" -idirafter $(src) -I$(native-build) \
 	-D__STDC_LIMIT_MACROS -D_JNI_IMPLEMENTATION_ -DAVIAN_VERSION=\"$(version)\" \
 	-DBOOT_CLASSPATH=\"[classpathJar]\"
diff --git a/src/compile.cpp b/src/compile.cpp
index d0e4dcc2cb..055106f334 100644
--- a/src/compile.cpp
+++ b/src/compile.cpp
@@ -5338,7 +5338,7 @@ compile(MyThread* t, object method)
           PROTECT(t, node);
 
           methodTree(t) = treeInsertNode
-            (t, methodTree(t), reinterpret_cast<intptr_t>
+            (t, &(context.zone), methodTree(t), reinterpret_cast<intptr_t>
              (&singletonValue(t, compiled, 0)), node, methodTreeSentinal(t),
              compareIpToMethodBounds);
         }
diff --git a/src/heapdump.cpp b/src/heapdump.cpp
index 6d17d82e5a..617d1d2e74 100644
--- a/src/heapdump.cpp
+++ b/src/heapdump.cpp
@@ -133,7 +133,7 @@ hash(object p, unsigned capacity)
 Set::Entry*
 find(Context* c, object p)
 {
-  if (c->objects == 0) return false;
+  if (c->objects == 0) return 0;
 
   for (int i = c->objects->index[hash(p, c->objects->capacity)]; i >= 0;) {
     Set::Entry* e = c->objects->entries + i;
@@ -143,7 +143,7 @@ find(Context* c, object p)
     i = e->next;
   }
 
-  return false;
+  return 0;
 }
 
 Set::Entry*
diff --git a/src/machine.cpp b/src/machine.cpp
index 8e53e35d6a..ab1bff60f0 100644
--- a/src/machine.cpp
+++ b/src/machine.cpp
@@ -482,9 +482,9 @@ void
 postCollect(Thread* t)
 {
 #ifdef VM_STRESS
-  t->m->heap->free(t->defaultHeap, Thread::HeapSizeInBytes);
+  t->m->heap->free(t->defaultHeap, ThreadHeapSizeInBytes);
   t->defaultHeap = static_cast<uintptr_t*>
-    (t->m->heap->allocate(Thread::HeapSizeInBytes));
+    (t->m->heap->allocate(ThreadHeapSizeInBytes));
 #endif
 
   t->heap = t->defaultHeap;
@@ -770,12 +770,8 @@ parseInterfaceTable(Thread* t, Stream& s, object class_, object pool)
     PROTECT(t, interfaceTable);
 
     unsigned i = 0;
-    object it = hashMapIterator(t, map);
-    PROTECT(t, it);
-
-    for (; it; it = hashMapIteratorNext(t, it)) {
-      object interface = resolveClass
-        (t, tripleFirst(t, hashMapIteratorNode(t, it)));
+    for (HashMapIterator it(t, map); it.hasMore();) {
+      object interface = resolveClass(t, tripleFirst(t, it.next()));
       if (UNLIKELY(t->exception)) return;
 
       set(t, interfaceTable, ArrayBody + (i * BytesPerWord), interface);
@@ -1243,10 +1239,8 @@ parseMethodTable(Thread* t, Stream& s, object class_, object pool)
     if (classFlags(t, class_) & ACC_INTERFACE) {
       PROTECT(t, vtable);
 
-      for (object it = hashMapIterator(t, virtualMap); it;
-           it = hashMapIteratorNext(t, it))
-      {
-        object method = tripleFirst(t, hashMapIteratorNode(t, it));
+      for (HashMapIterator it(t, virtualMap); it.hasMore();) {
+        object method = tripleFirst(t, it.next());
         assert(t, arrayBody(t, vtable, methodOffset(t, method)) == 0);
         set(t, vtable, ArrayBody + (methodOffset(t, method) * BytesPerWord),
             method);
@@ -1703,7 +1697,7 @@ Machine::dispose()
   }
 
   for (unsigned i = 0; i < heapPoolIndex; ++i) {
-    heap->free(heapPool[i], Thread::HeapSizeInBytes);
+    heap->free(heapPool[i], ThreadHeapSizeInBytes);
   }
 
   heap->free(properties, sizeof(const char*) * propertyCount);
@@ -1729,7 +1723,7 @@ Thread::Thread(Machine* m, object javaThread, Thread* parent):
   protector(0),
   runnable(this),
   defaultHeap(static_cast<uintptr_t*>
-              (m->heap->allocate(HeapSizeInBytes))),
+              (m->heap->allocate(ThreadHeapSizeInBytes))),
   heap(defaultHeap),
   backupHeap(0),
   backupHeapIndex(0),
@@ -1870,7 +1864,7 @@ Thread::dispose()
     systemThread->dispose();
   }
 
-  m->heap->free(defaultHeap, Thread::HeapSizeInBytes);
+  m->heap->free(defaultHeap, ThreadHeapSizeInBytes);
 
   m->processor->dispose(this);
 }
@@ -2028,7 +2022,7 @@ allocate2(Thread* t, unsigned sizeInBytes, bool objectMask)
 {
   return allocate3
     (t, t->m->heap,
-     ceiling(sizeInBytes, BytesPerWord) > Thread::HeapSizeInWords ?
+     ceiling(sizeInBytes, BytesPerWord) > ThreadHeapSizeInWords ?
      Machine::FixedAllocation : Machine::MovableAllocation,
      sizeInBytes, objectMask);
 }
@@ -2047,7 +2041,7 @@ allocate3(Thread* t, Allocator* allocator, Machine::AllocationType type,
     return o;
   } else if (t->tracing) {
     expect(t, t->heapIndex + ceiling(sizeInBytes, BytesPerWord)
-           <= Thread::HeapSizeInWords);
+           <= ThreadHeapSizeInWords);
     return allocateSmall(t, sizeInBytes);
   }
 
@@ -2058,26 +2052,33 @@ allocate3(Thread* t, Allocator* allocator, Machine::AllocationType type,
     // collection or some other reason.  We give it a chance here.
     ENTER(t, Thread::IdleState);
   }
-
-  if (type == Machine::FixedAllocation) {
-    if (t->m->fixedFootprint + sizeInBytes
-        > Machine::FixedFootprintThresholdInBytes)
+  
+  switch (type) {
+  case Machine::MovableAllocation:
+    if (t->heapIndex + ceiling(sizeInBytes, BytesPerWord)
+        > ThreadHeapSizeInWords)
     {
       t->heap = 0;
-    }
-  } else if (t->heapIndex + ceiling(sizeInBytes, BytesPerWord)
-             > Thread::HeapSizeInWords)
-  {
-    t->heap = 0;
-    if (t->m->heapPoolIndex < Machine::HeapPoolSize) {
-      t->heap = static_cast<uintptr_t*>
-        (t->m->heap->tryAllocate(Thread::HeapSizeInBytes));
-      if (t->heap) {
-        t->m->heapPool[t->m->heapPoolIndex++] = t->heap;
-        t->heapOffset += t->heapIndex;
-        t->heapIndex = 0;
+      if (t->m->heapPoolIndex < ThreadHeapPoolSize) {
+        t->heap = static_cast<uintptr_t*>
+          (t->m->heap->tryAllocate(ThreadHeapSizeInBytes));
+        if (t->heap) {
+          t->m->heapPool[t->m->heapPoolIndex++] = t->heap;
+          t->heapOffset += t->heapIndex;
+          t->heapIndex = 0;
+        }
       }
     }
+    break;
+
+  case Machine::FixedAllocation:
+    if (t->m->fixedFootprint + sizeInBytes > FixedFootprintThresholdInBytes) {
+      t->heap = 0;
+    }
+    break;
+
+  case Machine::ImmortalAllocation:
+    break;
   }
 
   if (t->heap == 0) {
@@ -2758,7 +2759,7 @@ collect(Thread* t, Heap::CollectionType type)
   killZombies(t, m->rootThread);
 
   for (unsigned i = 0; i < m->heapPoolIndex; ++i) {
-    m->heap->free(m->heapPool[i], Thread::HeapSizeInBytes);
+    m->heap->free(m->heapPool[i], ThreadHeapSizeInBytes);
   }
   m->heapPoolIndex = 0;
 
diff --git a/src/machine.h b/src/machine.h
index 2dab96f273..7b1e5a99ed 100644
--- a/src/machine.h
+++ b/src/machine.h
@@ -45,6 +45,14 @@ const uintptr_t HashTakenMark = 1;
 const uintptr_t ExtendedMark = 2;
 const uintptr_t FixedMark = 3;
 
+const unsigned ThreadHeapSizeInBytes = 64 * 1024;
+const unsigned ThreadHeapSizeInWords = ThreadHeapSizeInBytes / BytesPerWord;
+
+const unsigned ThreadHeapPoolSize = 64;
+
+const unsigned FixedFootprintThresholdInBytes
+= ThreadHeapPoolSize * ThreadHeapSizeInBytes;
+
 enum FieldCode {
   VoidField,
   ByteField,
@@ -1144,10 +1152,6 @@ class Machine {
     dispose();
   }
 
-  static const unsigned HeapPoolSize = 8;
-
-  static const unsigned FixedFootprintThresholdInBytes = 256 * 1024;
-
   void dispose();
 
   JavaVMVTable* vtable;
@@ -1184,7 +1188,7 @@ class Machine {
   bool unsafe;
   JavaVMVTable javaVMVTable;
   JNIEnvVTable jniEnvVTable;
-  uintptr_t* heapPool[HeapPoolSize];
+  uintptr_t* heapPool[ThreadHeapPoolSize];
   unsigned heapPoolIndex;
 };
 
@@ -1282,9 +1286,6 @@ class Thread {
     Thread* t;
   };
 
-  static const unsigned HeapSizeInBytes = 64 * 1024;
-  static const unsigned HeapSizeInWords = HeapSizeInBytes / BytesPerWord;
-
   Thread(Machine* m, object javaThread, Thread* parent);
 
   void init();
@@ -1452,7 +1453,7 @@ inline void
 ensure(Thread* t, unsigned sizeInBytes)
 {
   if (t->heapIndex + ceiling(sizeInBytes, BytesPerWord)
-      > Thread::HeapSizeInWords)
+      > ThreadHeapSizeInWords)
   {
     expect(t, t->backupHeap == 0);
     t->backupHeap = static_cast<uintptr_t*>
@@ -1484,7 +1485,7 @@ allocate(Thread* t, unsigned sizeInBytes, bool objectMask)
   stress(t);
 
   if (UNLIKELY(t->heapIndex + ceiling(sizeInBytes, BytesPerWord)
-               > Thread::HeapSizeInWords
+               > ThreadHeapSizeInWords
                or t->m->exclusive))
   {
     return allocate2(t, sizeInBytes, objectMask);
diff --git a/src/types.def b/src/types.def
index bfe450e16a..1fadf50e39 100644
--- a/src/types.def
+++ b/src/types.def
@@ -73,11 +73,6 @@
 (type weakHashMap
   (extends hashMap))
 
-(type hashMapIterator
-  (object map)
-  (object node)
-  (unsigned index))
-
 (type list
   (uint32_t size)
   (object front)
@@ -95,12 +90,6 @@
   (object value)
   (object left)
   (object right))
- 
-(type treePath
-  (uintptr_t fresh)
-  (object node)
-  (object root)
-  (object ancestors))
 
 (type callNode
   (intptr_t address)
diff --git a/src/util.cpp b/src/util.cpp
index 219695a536..f149e9c2e2 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -14,6 +14,54 @@ using namespace vm;
 
 namespace {
 
+class TreeContext {
+ public:
+  class Path {
+   public:
+    Path(object node, Path* next): node(node), next(next) { }
+
+    object node;
+    Path* next;
+  };
+
+  class MyProtector: public Thread::Protector {
+   public:
+    MyProtector(Thread* thread, TreeContext* context):
+      Protector(thread), context(context)
+    { }
+
+    virtual void visit(Heap::Visitor* v) {
+      v->visit(&(context->root));
+      v->visit(&(context->node));
+
+      for (Path* p = context->ancestors; p; p = p->next) {
+        v->visit(&(p->node));
+      }
+    }
+
+    TreeContext* context;
+  };
+
+  TreeContext(Thread* thread, Zone* zone):
+    zone(zone), root(0), node(0), ancestors(0), protector(thread, this),
+    fresh(false)
+  { }
+  
+  Zone* zone;
+  object root;
+  object node;
+  Path* ancestors;
+  MyProtector protector;
+  bool fresh;
+};
+
+TreeContext::Path*
+path(TreeContext* c, object node, TreeContext::Path* next)
+{
+  return new (c->zone->allocate(sizeof(TreeContext::Path)))
+    TreeContext::Path(node, next);
+}
+
 inline object
 getTreeNodeValue(Thread*, object n)
 {
@@ -58,8 +106,9 @@ cloneTreeNode(Thread* t, object n)
   return newNode;
 }
 
-object
-treeFind(Thread* t, object old, intptr_t key, object node, object sentinal,
+void
+treeFind(Thread* t, TreeContext* c, object old, intptr_t key, object node,
+         object sentinal,
          intptr_t (*compare)(Thread* t, intptr_t key, object b))
 {
   PROTECT(t, old);
@@ -72,11 +121,8 @@ treeFind(Thread* t, object old, intptr_t key, object node, object sentinal,
   object new_ = newRoot;
   PROTECT(t, new_);
 
-  object ancestors = 0;
-  PROTECT(t, ancestors);
-
   while (old != sentinal) {
-    ancestors = makePair(t, new_, ancestors);
+    c->ancestors = path(c, new_, c->ancestors);
 
     intptr_t difference = compare(t, key, getTreeNodeValue(t, old));
 
@@ -91,13 +137,20 @@ treeFind(Thread* t, object old, intptr_t key, object node, object sentinal,
       set(t, new_, TreeNodeRight, n);
       new_ = n;
     } else {
-      return makeTreePath(t, false, new_, newRoot, pairSecond(t, ancestors));
+      c->fresh = false;
+      c->root = newRoot;
+      c->node = new_;
+      c->ancestors = c->ancestors->next;
+      return;
     }
   }
 
   setTreeNodeValue(t, new_, getTreeNodeValue(t, node));
 
-  return makeTreePath(t, true, new_, newRoot, ancestors);
+  c->fresh = true;
+  c->root = newRoot;
+  c->node = new_;
+  c->ancestors = c->ancestors;
 }
 
 object
@@ -123,122 +176,109 @@ rightRotate(Thread* t, object n)
 }
 
 object
-treeAdd(Thread* t, object path)
+treeAdd(Thread* t, TreeContext* c)
 {
-  object new_ = treePathNode(t, path);
+  object new_ = c->node;
   PROTECT(t, new_);
 
-  object newRoot = treePathRoot(t, path);
+  object newRoot = c->root;
   PROTECT(t, newRoot);
 
-  object ancestors = treePathAncestors(t, path);
-  PROTECT(t, ancestors);
-
   // rebalance
   setTreeNodeRed(t, new_, true);
-  while (ancestors != 0 and treeNodeRed(t, pairFirst(t, ancestors))) {
-    if (pairFirst(t, ancestors)
-        == treeNodeLeft(t, pairFirst(t, pairSecond(t, ancestors))))
+  while (c->ancestors != 0 and treeNodeRed(t, c->ancestors->node)) {
+    if (c->ancestors->node
+        == treeNodeLeft(t, c->ancestors->next->node))
     {
       if (treeNodeRed
-          (t, treeNodeRight(t, pairFirst(t, pairSecond(t, ancestors)))))
+          (t, treeNodeRight(t, c->ancestors->next->node)))
       {
-        setTreeNodeRed(t, pairFirst(t, ancestors), true);
+        setTreeNodeRed(t, c->ancestors->node, false);
 
         object n = cloneTreeNode
-          (t, treeNodeRight(t, pairFirst(t, pairSecond(t, ancestors))));
+          (t, treeNodeRight(t, c->ancestors->next->node));
 
-        set(t, pairFirst(t, pairSecond(t, ancestors)), TreeNodeRight, n);
+        set(t, c->ancestors->next->node, TreeNodeRight, n);
 
-        setTreeNodeRed
-          (t, treeNodeRight
-           (t, pairFirst(t, pairSecond(t, ancestors))), false);
+        setTreeNodeRed(t, treeNodeRight(t, c->ancestors->next->node), false);
 
-        setTreeNodeRed(t, pairFirst(t, pairSecond(t, ancestors)), false);
+        setTreeNodeRed(t, c->ancestors->next->node, true);
 
-        new_ = pairFirst(t, pairSecond(t, ancestors));
-        ancestors = pairSecond(t, pairSecond(t, ancestors));
+        new_ = c->ancestors->next->node;
+        c->ancestors = c->ancestors->next->next;
       } else {
-        if (new_ == treeNodeRight(t, pairFirst(t, ancestors))) {
-          new_ = pairFirst(t, ancestors);
-          ancestors = pairSecond(t, ancestors);
+        if (new_ == treeNodeRight(t, c->ancestors->node)) {
+          new_ = c->ancestors->node;
+          c->ancestors = c->ancestors->next;
 
           object n = leftRotate(t, new_);
 
-          if (new_ == treeNodeRight(t, pairFirst(t, ancestors))) {
-            set(t, pairFirst(t, ancestors), TreeNodeRight, n);
+          if (new_ == treeNodeRight(t, c->ancestors->node)) {
+            set(t, c->ancestors->node, TreeNodeRight, n);
           } else {
-            set(t, pairFirst(t, ancestors), TreeNodeLeft, n);
+            set(t, c->ancestors->node, TreeNodeLeft, n);
           }
-          ancestors = makePair(t, n, ancestors);
+          c->ancestors = path(c, n, c->ancestors);
         }
-        setTreeNodeRed(t, pairFirst(t, ancestors), false);
-        setTreeNodeRed(t, pairFirst(t, pairSecond(t, ancestors)), true);
+        setTreeNodeRed(t, c->ancestors->node, false);
+        setTreeNodeRed(t, c->ancestors->next->node, true);
 
-        object n = rightRotate(t, pairFirst(t, pairSecond(t, ancestors)));
-        if (pairSecond(t, pairSecond(t, ancestors)) == 0) {
+        object n = rightRotate(t, c->ancestors->next->node);
+        if (c->ancestors->next->next == 0) {
           newRoot = n;
-        } else if (treeNodeRight
-                   (t, pairFirst(t, pairSecond(t, pairSecond(t, ancestors))))
-                   == pairFirst(t, pairSecond(t, ancestors)))
+        } else if (treeNodeRight(t, c->ancestors->next->next->node)
+                   == c->ancestors->next->node)
         {
-          set(t, pairFirst(t, pairSecond(t, pairSecond(t, ancestors))),
-              TreeNodeRight, n);
+          set(t, c->ancestors->next->next->node, TreeNodeRight, n);
         } else {
-          set(t, pairFirst(t, pairSecond(t, pairSecond(t, ancestors))),
-              TreeNodeLeft, n);
+          set(t, c->ancestors->next->next->node, TreeNodeLeft, n);
         }
         // done
       }
     } else { // this is just the reverse of the code above (right and
              // left swapped):
       if (treeNodeRed
-          (t, treeNodeLeft(t, pairFirst(t, pairSecond(t, ancestors)))))
+          (t, treeNodeLeft(t, c->ancestors->next->node)))
       {
-        setTreeNodeRed(t, pairFirst(t, ancestors), true);
+        setTreeNodeRed(t, c->ancestors->node, false);
 
         object n = cloneTreeNode
-          (t, treeNodeLeft(t, pairFirst(t, pairSecond(t, ancestors))));
+          (t, treeNodeLeft(t, c->ancestors->next->node));
 
-        set(t, pairFirst(t, pairSecond(t, ancestors)), TreeNodeLeft, n);
+        set(t, c->ancestors->next->node, TreeNodeLeft, n);
 
-        setTreeNodeRed
-          (t, treeNodeLeft
-           (t, pairFirst(t, pairSecond(t, ancestors))), false);
+        setTreeNodeRed(t, treeNodeLeft(t, c->ancestors->next->node), false);
 
-        setTreeNodeRed(t, pairFirst(t, pairSecond(t, ancestors)), false);
+        setTreeNodeRed(t, c->ancestors->next->node, true);
 
-        new_ = pairFirst(t, pairSecond(t, ancestors));
-        ancestors = pairSecond(t, pairSecond(t, ancestors));
+        new_ = c->ancestors->next->node;
+        c->ancestors = c->ancestors->next->next;
       } else {
-        if (new_ == treeNodeLeft(t, pairFirst(t, ancestors))) {
-          new_ = pairFirst(t, ancestors);
-          ancestors = pairSecond(t, ancestors);
+        if (new_ == treeNodeLeft(t, c->ancestors->node)) {
+          new_ = c->ancestors->node;
+          c->ancestors = c->ancestors->next;
 
           object n = rightRotate(t, new_);
 
-          if (new_ == treeNodeLeft(t, pairFirst(t, ancestors))) {
-            set(t, pairFirst(t, ancestors), TreeNodeLeft, n);
+          if (new_ == treeNodeLeft(t, c->ancestors->node)) {
+            set(t, c->ancestors->node, TreeNodeLeft, n);
           } else {
-            set(t, pairFirst(t, ancestors), TreeNodeRight, n);
+            set(t, c->ancestors->node, TreeNodeRight, n);
           }
-          ancestors = makePair(t, n, ancestors);
+          c->ancestors = path(c, n, c->ancestors);
         }
-        setTreeNodeRed(t, pairFirst(t, ancestors), false);
-        setTreeNodeRed(t, pairFirst(t, pairSecond(t, ancestors)), true);
+        setTreeNodeRed(t, c->ancestors->node, false);
+        setTreeNodeRed(t, c->ancestors->next->node, true);
 
-        object n = leftRotate(t, pairFirst(t, pairSecond(t, ancestors)));
-        if (pairSecond(t, pairSecond(t, ancestors)) == 0) {
+        object n = leftRotate(t, c->ancestors->next->node);
+        if (c->ancestors->next->next == 0) {
           newRoot = n;
-        } else if (treeNodeLeft
-                   (t, pairFirst(t, pairSecond(t, pairSecond(t, ancestors))))
-                   == pairFirst(t, pairSecond(t, ancestors)))
+        } else if (treeNodeLeft(t, c->ancestors->next->next->node)
+                   == c->ancestors->next->node)
         {
-          set(t, pairFirst(t, pairSecond(t, pairSecond(t, ancestors))),
-              TreeNodeLeft, n);
+          set(t, c->ancestors->next->next->node, TreeNodeLeft, n);
         } else {
-          set(t, pairFirst(t, pairSecond(t, pairSecond(t, ancestors))),
-              TreeNodeRight, n);
+          set(t, c->ancestors->next->next->node, TreeNodeRight, n);
         }
         // done
       }
@@ -442,40 +482,6 @@ hashMapRemove(Thread* t, object map, object key,
   return o;
 }
 
-object
-hashMapIterator(Thread* t, object map)
-{
-  object array = hashMapArray(t, map);
-  if (array) {
-    for (unsigned i = 0; i < arrayLength(t, array); ++i) {
-      if (arrayBody(t, array, i)) {
-        return makeHashMapIterator(t, map, arrayBody(t, array, i), i + 1);
-      }
-    }
-  }
-  return 0;
-}
-
-object
-hashMapIteratorNext(Thread* t, object it)
-{
-  object map = hashMapIteratorMap(t, it);
-  object node = hashMapIteratorNode(t, it);
-  unsigned index = hashMapIteratorIndex(t, it);
-
-  if (tripleThird(t, node)) {
-    return makeHashMapIterator(t, map, tripleThird(t, node), index);
-  } else {
-    object array = hashMapArray(t, map);
-    for (unsigned i = index; i < arrayLength(t, array); ++i) {
-      if (arrayBody(t, array, i)) {
-        return makeHashMapIterator(t, map, arrayBody(t, array, i), i + 1);
-      }
-    }
-    return 0;
-  }  
-}
-
 void
 listAppend(Thread* t, object list, object value)
 {
@@ -541,16 +547,18 @@ treeQuery(Thread* t, object tree, intptr_t key, object sentinal,
 }
 
 object
-treeInsertNode(Thread* t, object tree, intptr_t key, object node,
+treeInsertNode(Thread* t, Zone* zone, object tree, intptr_t key, object node,
                object sentinal,
                intptr_t (*compare)(Thread* t, intptr_t key, object b))
 {
   PROTECT(t, tree);
   PROTECT(t, sentinal);
 
-  object path = treeFind(t, tree, key, node, sentinal, compare);
-  expect(t, treePathFresh(t, path));
-  return treeAdd(t, path);
+  TreeContext c(t, zone);
+  treeFind(t, &c, tree, key, node, sentinal, compare);
+  expect(t, c.fresh);
+
+  return treeAdd(t, &c);
 }
 
 } // namespace vm
diff --git a/src/util.h b/src/util.h
index adf8487723..ea8fc8b09c 100644
--- a/src/util.h
+++ b/src/util.h
@@ -12,6 +12,7 @@
 #define UTIL_H
 
 #include "machine.h"
+#include "zone.h"
 
 namespace vm {
 
@@ -88,10 +89,58 @@ treeQuery(Thread* t, object tree, intptr_t key, object sentinal,
           intptr_t (*compare)(Thread* t, intptr_t key, object b));
 
 object
-treeInsertNode(Thread* t, object tree, intptr_t key, object node,
+treeInsertNode(Thread* t, Zone* zone, object tree, intptr_t key, object node,
                object sentinal,
                intptr_t (*compare)(Thread* t, intptr_t key, object b));
 
+class HashMapIterator: public Thread::Protector {
+ public:
+  HashMapIterator(Thread* t, object map):
+    Protector(t), map(map), node(0), index(0)
+  {
+    find();
+  }
+
+  void find() {
+    object array = hashMapArray(t, map);
+    for (unsigned i = index; i < arrayLength(t, array); ++i) {
+      if (arrayBody(t, array, i)) {
+        node = arrayBody(t, array, i);
+        index = i + 1;
+        return;
+      }
+    }
+    node = 0;
+  }
+
+  bool hasMore() {
+    return node != 0;
+  }
+
+  object next() {
+    if (node) {
+      object n = node;
+      if (tripleThird(t, node)) {
+        node = tripleThird(t, node);
+      } else {
+        find();
+      }
+      return n;
+    } else {
+      return 0;
+    }
+  }
+
+  virtual void visit(Heap::Visitor* v) {
+    v->visit(&map);
+    v->visit(&node);
+  }
+
+  object map;
+  object node;
+  unsigned index;
+};
+
 } // vm
 
 #endif//UTIL_H