--- jsr166/src/jsr166e/extra/ReadMostlyVector.java	2011/07/16 15:05:04	1.4
+++ jsr166/src/jsr166e/extra/ReadMostlyVector.java	2015/01/18 20:17:33	1.35
@@ -5,7 +5,8 @@
  */
 
 package jsr166e.extra;
-import jsr166e.*;
+
+import jsr166e.StampedLock;
 import java.util.*;
 
 /**
@@ -14,12 +15,15 @@ import java.util.*;
  * throughput when invocations of read-only methods by multiple
  * threads are most common.
  *
- * <p> The iterators returned by this class's {@link #iterator()
+ * <p>The iterators returned by this class's {@link #iterator()
  * iterator} and {@link #listIterator(int) listIterator} methods are
  * best-effort in the presence of concurrent modifications, and do
  * <em>NOT</em> throw {@link ConcurrentModificationException}.  An
  * iterator's {@code next()} method returns consecutive elements as
- * they appear in the underlying array upon each access.
+ * they appear in the underlying array upon each access. Alternatively,
+ * method {@link #snapshotIterator} may be used for deterministic
+ * traversals, at the expense of making a copy, and unavailability of
+ * method {@code Iterator.remove}.
  *
  * <p>Otherwise, this class supports all methods, under the same
  * documented specifications, as {@code Vector}.  Consult {@link
@@ -29,7 +33,8 @@ import java.util.*;
  *
  * @author Doug Lea
  */
-public class ReadMostlyVector<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
+public class ReadMostlyVector<E>
+        implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
     private static final long serialVersionUID = 8673264195747942595L;
 
     /*
@@ -45,6 +50,11 @@ public class ReadMostlyVector<E> impleme
      * read-only mode, and then lock. When in read-only mode, they
      * validate only at the end of an array scan unless the element is
      * actually used (for example, as an argument of method equals).
+     *
+     * We rely on some invariants that are always true, even for field
+     * reads in read-only mode that have not yet been validated:
+     * - array != null
+     * - count >= 0
      */
 
     /**
@@ -53,9 +63,9 @@ public class ReadMostlyVector<E> impleme
      */
     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
 
-    // fields are non-private to simpify nested class access
+    // fields are non-private to simplify nested class access
     Object[] array;
-    final SequenceLock lock;
+    final StampedLock lock;
     int count;
     final int capacityIncrement;
 
@@ -77,14 +87,13 @@ public class ReadMostlyVector<E> impleme
                                                initialCapacity);
         this.array = new Object[initialCapacity];
         this.capacityIncrement = capacityIncrement;
-        this.lock = new SequenceLock();
+        this.lock = new StampedLock();
     }
 
     /**
      * Creates an empty vector with the given initial capacity.
      *
      * @param initialCapacity the initial capacity of the underlying array
-     *
      * @throws IllegalArgumentException if initial capacity is negative
      */
     public ReadMostlyVector(int initialCapacity) {
@@ -92,10 +101,11 @@ public class ReadMostlyVector<E> impleme
     }
 
     /**
-     * Creates an empty vector with an underlying array of size {@code 10}.
+     * Creates an empty vector.
      */
     public ReadMostlyVector() {
-        this(10, 0);
+        this.capacityIncrement = 0;
+        this.lock = new StampedLock();
     }
 
     /**
@@ -114,7 +124,7 @@ public class ReadMostlyVector<E> impleme
         this.array = elements;
         this.count = elements.length;
         this.capacityIncrement = 0;
-        this.lock = new SequenceLock();
+        this.lock = new StampedLock();
     }
 
     // internal constructor for clone
@@ -122,27 +132,35 @@ public class ReadMostlyVector<E> impleme
         this.array = array;
         this.count = count;
         this.capacityIncrement = capacityIncrement;
-        this.lock = new SequenceLock();
+        this.lock = new StampedLock();
     }
 
+    static final int INITIAL_CAP = 16;
+
     // For explanation, see CopyOnWriteArrayList
-    final void grow(int minCapacity) {
-        int oldCapacity = array.length;
-        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
+    final Object[] grow(int minCapacity) {
+        Object[] items;
+        int newCapacity;
+        if ((items = array) == null)
+            newCapacity = INITIAL_CAP;
+        else {
+            int oldCapacity = array.length;
+            newCapacity = oldCapacity + ((capacityIncrement > 0) ?
                                          capacityIncrement : oldCapacity);
+        }
         if (newCapacity - minCapacity < 0)
             newCapacity = minCapacity;
-        if (newCapacity - MAX_ARRAY_SIZE > 0)
-            newCapacity = hugeCapacity(minCapacity);
-        array = Arrays.copyOf(array, newCapacity);
-    }
-
-    static int hugeCapacity(int minCapacity) {
-        if (minCapacity < 0) // overflow
-            throw new OutOfMemoryError();
-        return (minCapacity > MAX_ARRAY_SIZE) ?
-            Integer.MAX_VALUE :
-            MAX_ARRAY_SIZE;
+        if (newCapacity - MAX_ARRAY_SIZE > 0) {
+            if (minCapacity < 0) // overflow
+                throw new OutOfMemoryError();
+            else if (minCapacity > MAX_ARRAY_SIZE)
+                newCapacity = Integer.MAX_VALUE;
+            else
+                newCapacity = MAX_ARRAY_SIZE;
+        }
+        return array = ((items == null) ?
+                        new Object[newCapacity] :
+                        Arrays.copyOf(items, newCapacity));
     }
 
     /*
@@ -151,97 +169,84 @@ public class ReadMostlyVector<E> impleme
      * as well as sublist and iterator classes.
      */
 
-    // Version of indexOf that returns -1 if either not present or invalid
-    final int validatedIndexOf(Object x, Object[] items, int index, int fence,
-                               long seq) {
-        for (int i = index; i < fence; ++i) {
-            Object e = items[i];
-            if (lock.getSequence() != seq)
-                break;
-            if (x == null? e == null : x.equals(e))
-                return i;
-        }
-        return -1;
-    }
-
-    final int rawIndexOf(Object x, int index, int fence) {
-        Object[] items = array;
-        for (int i = index; i < fence; ++i) {
-            Object e = items[i];
-            if (x == null? e == null : x.equals(e))
-                return i;
-        }
-        return -1;
-    }
-
-    final int validatedLastIndexOf(Object x, Object[] items,
-                                   int index, int origin, long seq) {
-        for (int i = index; i >= origin; --i) {
-            Object e = items[i];
-            if (lock.getSequence() != seq)
-                break;
-            if (x == null? e == null : x.equals(e))
-                return i;
+    static int findFirstIndex(Object[] items, Object x, int index, int fence) {
+        int len;
+        if (items != null && (len = items.length) > 0) {
+            int start = (index < 0) ? 0 : index;
+            int bound = (fence < len) ? fence : len;
+            for (int i = start; i < bound; ++i) {
+                Object e = items[i];
+                if ((x == null) ? e == null : x.equals(e))
+                    return i;
+            }
         }
         return -1;
     }
 
-    final int rawLastIndexOf(Object x, int index, int origin) {
-        Object[] items = array;
-        for (int i = index; i >= origin; --i) {
-            Object e = items[i];
-            if (x == null? e == null : x.equals(e))
-                return i;
+    static int findLastIndex(Object[] items, Object x, int index, int origin) {
+        int len;
+        if (items != null && (len = items.length) > 0) {
+            int last = (index < len) ? index : len - 1;
+            int start = (origin < 0) ? 0 : origin;
+            for (int i = last; i >= start; --i) {
+                Object e = items[i];
+                if ((x == null) ? e == null : x.equals(e))
+                    return i;
+            }
         }
         return -1;
     }
 
-    final void rawAdd(Object e) {
+    final void rawAdd(E e) {
         int n = count;
-        if (n >= array.length)
-            grow(n + 1);
-        array[n] = e;
+        Object[] items = array;
+        if (items == null || n >= items.length)
+            items = grow(n + 1);
+        items[n] = e;
         count = n + 1;
     }
 
-    final void rawAddAt(int index, Object e) {
+    final void rawAddAt(int index, E e) {
         int n = count;
+        Object[] items = array;
         if (index > n)
             throw new ArrayIndexOutOfBoundsException(index);
-        if (n >= array.length)
-            grow(n + 1);
+        if (items == null || n >= items.length)
+            items = grow(n + 1);
         if (index < n)
-            System.arraycopy(array, index, array, index + 1, n - index);
-        array[index] = e;
+            System.arraycopy(items, index, items, index + 1, n - index);
+        items[index] = e;
         count = n + 1;
     }
 
     final boolean rawAddAllAt(int index, Object[] elements) {
         int n = count;
+        Object[] items = array;
         if (index < 0 || index > n)
             throw new ArrayIndexOutOfBoundsException(index);
         int len = elements.length;
         if (len == 0)
             return false;
         int newCount = n + len;
-        if (newCount >= array.length)
-            grow(newCount);
-        int mv = count - index;
+        if (items == null || newCount >= items.length)
+            items = grow(newCount);
+        int mv = n - index;
         if (mv > 0)
-            System.arraycopy(array, index, array, index + len, mv);
-        System.arraycopy(elements, 0, array, index, len);
+            System.arraycopy(items, index, items, index + len, mv);
+        System.arraycopy(elements, 0, items, index, len);
         count = newCount;
         return true;
     }
 
     final boolean rawRemoveAt(int index) {
         int n = count - 1;
-        if (index < 0 || index > n)
+        Object[] items = array;
+        if (items == null || index < 0 || index > n)
             return false;
         int mv = n - index;
         if (mv > 0)
-            System.arraycopy(array, index + 1, array, index, mv);
-        array[n] = null;
+            System.arraycopy(items, index + 1, items, index, mv);
+        items[n] = null;
         count = n;
         return true;
     }
@@ -253,314 +258,229 @@ public class ReadMostlyVector<E> impleme
      * is left negative if the bound should be determined via count
      * field under lock.
      */
-    final boolean internalRemoveAll(Collection<?> c, int origin, int bound) {
-        SequenceLock lock = this.lock;
+    final boolean lockedRemoveAll(Collection<?> c, int origin, int bound) {
         boolean removed = false;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
             int n = count;
             int fence = bound < 0 || bound > n ? n : bound;
             if (origin >= 0 && origin < fence) {
                 for (Object x : c) {
-                    while (rawRemoveAt(rawIndexOf(x, origin, fence)))
+                    while (rawRemoveAt(findFirstIndex(array, x, origin, fence)))
                         removed = true;
                 }
             }
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
         return removed;
     }
 
-    final boolean internalRetainAll(Collection<?> c, int origin, int bound) {
-        SequenceLock lock = this.lock;
+    final boolean lockedRetainAll(Collection<?> c, int origin, int bound) {
+        final StampedLock lock = this.lock;
         boolean removed = false;
         if (c != this) {
-            lock.lock();
+            long stamp = lock.writeLock();
             try {
-                int i = origin;
-                int n = count;
-                int fence = bound < 0 || bound > n ? n : bound;
-                while (i >= 0 && i < fence) {
-                    if (c.contains(array[i]))
-                        ++i;
-                    else {
-                        --fence;
-                        int mv = --count - i;
-                        if (mv > 0)
-                            System.arraycopy(array, i + 1, array, i, mv);
+                Object[] items;
+                int i, n;
+                if ((items = array) != null && (n = count) > 0 &&
+                    n < items.length && (i = origin) >= 0) {
+                    int fence = bound < 0 || bound > n ? n : bound;
+                    while (i < fence) {
+                        if (c.contains(items[i]))
+                            ++i;
+                        else {
+                            --fence;
+                            int mv = --n - i;
+                            if (mv > 0)
+                                System.arraycopy(items, i + 1, items, i, mv);
+                        }
+                    }
+                    if (count != n) {
+                        count = n;
                         removed = true;
                     }
                 }
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
         }
         return removed;
     }
 
     final void internalClear(int origin, int bound) {
-        int n = count;
-        int fence = bound < 0 || bound > n ? n : bound;
-        if (origin >= 0 && origin < fence) {
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if (origin < 0)
+                origin = 0;
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
             int removed = fence - origin;
             int newCount = n - removed;
             int mv = n - (origin + removed);
             if (mv > 0)
-                System.arraycopy(array, origin + removed, array, origin, mv);
+                System.arraycopy(items, origin + removed, items, origin, mv);
             for (int i = n; i < newCount; ++i)
-                array[i] = null;
+                items[i] = null;
             count = newCount;
         }
     }
 
     final boolean internalContainsAll(Collection<?> c, int origin, int bound) {
-        SequenceLock lock = this.lock;
-        boolean contained;
-        boolean locked = false;
-        try {
-            for (;;) {
-                long seq = lock.awaitAvailability();
-                Object[] items = array;
-                int len = items.length;
-                int n = count;
-                if (n > len)
-                    continue;
-                int fence = bound < 0 || bound > n ? n : bound;
-                if (origin < 0)
-                    contained = false;
-                else {
-                    contained = true;
-                    for (Object e : c) {
-                        int idx = (locked?
-                                   rawIndexOf(e, origin, fence) :
-                                   validatedIndexOf(e, items, origin,
-                                                    fence, seq));
-                        if (idx < 0) {
-                            contained = false;
-                            break;
-                        }
-                    }
-                }
-                if (lock.getSequence() == seq)
-                    break;
-                lock.lock();
-                locked = true;
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if (origin < 0)
+                origin = 0;
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
+            for (Object e : c) {
+                if (findFirstIndex(items, e, origin, fence) < 0)
+                    return false;
             }
-        } finally {
-            if (locked)
-                lock.unlock();
         }
-        return contained;
+        else if (!c.isEmpty())
+            return false;
+        return true;
     }
 
     final boolean internalEquals(List<?> list, int origin, int bound) {
-        SequenceLock lock = this.lock;
-        boolean locked = false;
-        boolean equal;
-        try {
-            for (;;) {
-                long seq = lock.awaitAvailability();
-                Object[] items = array;
-                int n = count;
-                if (n > items.length || origin < 0)
-                    equal = false;
-                else {
-                    equal = true;
-                    int fence = bound < 0 || bound > n ? n : bound;
-                    Iterator<?> it = list.iterator();
-                    for (int i = origin; i < fence; ++i) {
-                        Object x = items[i];
-                        Object y;
-                        if ((!locked && lock.getSequence() != seq) ||
-                            !it.hasNext() ||
-                            (y = it.next()) == null ?
-                            x != null : !y.equals(x)) {
-                            equal = false;
-                            break;
-                        }
-                    }
-                    if (equal && it.hasNext())
-                        equal = false;
-                }
-                if (lock.getSequence() == seq)
-                    break;
-                lock.lock();
-                locked = true;
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if (origin < 0)
+                origin = 0;
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
+            Iterator<?> it = list.iterator();
+            for (int i = origin; i < fence; ++i) {
+                if (!it.hasNext())
+                    return false;
+                Object y = it.next();
+                Object x = items[i];
+                if (x != y && (x == null || !x.equals(y)))
+                    return false;
             }
-        } finally {
-            if (locked)
-                lock.unlock();
+            if (it.hasNext())
+                return false;
         }
-        return equal;
+        else if (!list.isEmpty())
+            return false;
+        return true;
     }
 
     final int internalHashCode(int origin, int bound) {
-        SequenceLock lock = this.lock;
-        int hash;
-        boolean locked = false;
-        try {
-            for (;;) {
-                hash = 1;
-                long seq = lock.awaitAvailability();
-                Object[] items = array;
-                int len = items.length;
-                int n = count;
-                if (n > len)
-                    continue;
-                int fence = bound < 0 || bound > n ? n : bound;
-                if (origin >= 0) {
-                    for (int i = origin; i < fence; ++i) {
-                        Object e = items[i];
-                        hash = 31*hash + (e == null ? 0 : e.hashCode());
-                    }
-                }
-                if (lock.getSequence() == seq)
-                    break;
-                lock.lock();
-                locked = true;
+        int hash = 1;
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if (origin < 0)
+                origin = 0;
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
+            for (int i = origin; i < fence; ++i) {
+                Object e = items[i];
+                hash = 31*hash + (e == null ? 0 : e.hashCode());
             }
-        } finally {
-            if (locked)
-                lock.unlock();
         }
         return hash;
     }
 
     final String internalToString(int origin, int bound) {
-        SequenceLock lock = this.lock;
-        String ret;
-        boolean locked = false;
-        try {
-            outer:for (;;) {
-                long seq = lock.awaitAvailability();
-                Object[] items = array;
-                int len = items.length;
-                int n = count;
-                if (n > len)
-                    continue;
-                int fence = bound < 0 || bound > n ? n : bound;
-                if (origin < 0 || origin == fence)
-                    ret = "[]";
-                else {
-                    StringBuilder sb = new StringBuilder();
-                    sb.append('[');
-                    for (int i = origin;;) {
-                        Object e = items[i];
-                        if (e == this)
-                            sb.append("(this Collection)");
-                        else if (!locked && lock.getSequence() != seq)
-                            continue outer;
-                        else
-                            sb.append(e.toString());
-                        if (++i < fence)
-                            sb.append(',').append(' ');
-                        else {
-                            ret = sb.append(']').toString();
-                            break;
-                        }
-                    }
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
+            int i = (origin < 0) ? 0 : origin;
+            if (i != fence) {
+                StringBuilder sb = new StringBuilder();
+                sb.append('[');
+                for (;;) {
+                    Object e = items[i];
+                    sb.append((e == this) ? "(this Collection)" : e.toString());
+                    if (++i < fence)
+                        sb.append(',').append(' ');
+                    else
+                        return sb.append(']').toString();
                 }
-                if (lock.getSequence() == seq)
-                    break;
-                lock.lock();
-                locked = true;
             }
-        } finally {
-            if (locked)
-                lock.unlock();
         }
-        return ret;
+        return "[]";
     }
 
     final Object[] internalToArray(int origin, int bound) {
-        Object[] result;
-        SequenceLock lock = this.lock;
-        boolean locked = false;
-        try {
-            for (;;) {
-                result = null;
-                long seq = lock.awaitAvailability();
-                Object[] items = array;
-                int len = items.length;
-                int n = count;
-                if (n > len)
-                    continue;
-                int fence = bound < 0 || bound > n ? n : bound;
-                if (origin >= 0)
-                    result = Arrays.copyOfRange(items, origin, fence,
-                                                Object[].class);
-                if (lock.getSequence() == seq)
-                    break;
-                lock.lock();
-                locked = true;
-            }
-        } finally {
-            if (locked)
-                lock.unlock();
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if (origin < 0)
+                origin = 0;
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
+            int i = (origin < 0) ? 0 : origin;
+            if (i != fence)
+                return Arrays.copyOfRange(items, i, fence, Object[].class);
         }
-        return result;
+        return new Object[0];
     }
 
+    @SuppressWarnings("unchecked")
     final <T> T[] internalToArray(T[] a, int origin, int bound) {
         int alen = a.length;
-        T[] result;
-        SequenceLock lock = this.lock;
-        boolean locked = false;
-        try {
-            for (;;) {
-                long seq = lock.awaitAvailability();
-                Object[] items = array;
-                int len = items.length;
-                int n = count;
-                if (n > len)
-                    continue;
-                int fence = bound < 0 || bound > n ? n : bound;
-                int rlen = fence - origin;
-                if (rlen < 0)
-                    rlen = 0;
-                if (origin < 0 || alen >= rlen) {
-                    if (rlen > 0)
-                        System.arraycopy(array, 0, a, origin, rlen);
+        Object[] items;
+        int n, len;
+        if ((items = array) != null && (len = items.length) > 0) {
+            if (origin < 0)
+                origin = 0;
+            if ((n = count) > len)
+                n = len;
+            int fence = bound < 0 || bound > n ? n : bound;
+            int i = (origin < 0) ? 0 : origin;
+            int rlen = fence - origin;
+            if (rlen > 0) {
+                if (alen >= rlen) {
+                    System.arraycopy(items, 0, a, origin, rlen);
                     if (alen > rlen)
                         a[rlen] = null;
-                    result = a;
+                    return a;
                 }
-                else
-                    result = (T[]) Arrays.copyOfRange(array, origin,
-                                                      fence, a.getClass());
-                if (lock.getSequence() == seq)
-                    break;
-                lock.lock();
-                locked = true;
+                return (T[]) Arrays.copyOfRange(items, i, fence, a.getClass());
             }
-        } finally {
-            if (locked)
-                lock.unlock();
         }
-        return result;
+        if (alen > 0)
+            a[0] = null;
+        return a;
     }
 
     // public List methods
 
     public boolean add(E e) {
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
             rawAdd(e);
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
         return true;
     }
 
     public void add(int index, E element) {
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
             rawAddAt(index, element);
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
     }
 
@@ -569,42 +489,48 @@ public class ReadMostlyVector<E> impleme
         int len = elements.length;
         if (len == 0)
             return false;
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            int newCount = count + len;
-            if (newCount >= array.length)
-                grow(newCount);
-            System.arraycopy(elements, 0, array, count, len);
+            Object[] items = array;
+            int n = count;
+            int newCount = n + len;
+            if (items == null || newCount >= items.length)
+                items = grow(newCount);
+            System.arraycopy(elements, 0, items, n, len);
             count = newCount;
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
         return true;
     }
 
     public boolean addAll(int index, Collection<? extends E> c) {
-        SequenceLock lock = this.lock;
-        boolean ret;
         Object[] elements = c.toArray();
-        lock.lock();
+        boolean ret;
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
             ret = rawAddAllAt(index, elements);
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
         return ret;
     }
 
     public void clear() {
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            for (int i = 0; i < count; i++)
-                array[i] = null;
+            int n = count;
+            Object[] items = array;
+            if (items != null) {
+                for (int i = 0; i < n; i++)
+                    items[i] = null;
+            }
             count = 0;
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
     }
 
@@ -613,7 +539,15 @@ public class ReadMostlyVector<E> impleme
     }
 
     public boolean containsAll(Collection<?> c) {
-        return internalContainsAll(c, 0, -1);
+        boolean ret;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            ret = internalContainsAll(c, 0, -1);
+        } finally {
+            lock.unlockRead(stamp);
+        }
+        return ret;
     }
 
     public boolean equals(Object o) {
@@ -621,201 +555,251 @@ public class ReadMostlyVector<E> impleme
             return true;
         if (!(o instanceof List))
             return false;
-        return internalEquals((List<?>)o, 0, -1);
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            return internalEquals((List<?>)o, 0, -1);
+        } finally {
+            lock.unlockRead(stamp);
+        }
     }
 
     public E get(int index) {
-        SequenceLock lock = this.lock;
-        for (;;) {
-            long seq = lock.awaitAvailability();
-            Object[] items = array;
-            int n = count;
-            if (n > items.length)
-                continue;
-            Object e; boolean ex;
-            if (index < 0 || index >= n) {
-                e = null;
-                ex = true;
-            }
-            else {
-                e = items[index];
-                ex = false;
-            }
-            if (lock.getSequence() == seq) {
-                if (ex)
-                    throw new ArrayIndexOutOfBoundsException(index);
-                else
-                    return (E)e;
-            }
+        final StampedLock lock = this.lock;
+        long stamp = lock.tryOptimisticRead();
+        Object[] items;
+        if (index >= 0 && (items = array) != null &&
+            index < count && index < items.length) {
+            @SuppressWarnings("unchecked") E e = (E)items[index];
+            if (lock.validate(stamp))
+                return e;
+        }
+        return lockedGet(index);
+    }
+
+    @SuppressWarnings("unchecked") private E lockedGet(int index) {
+        boolean oobe = false;
+        E e = null;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            Object[] items;
+            if ((items = array) != null && index < items.length &&
+                index < count && index >= 0)
+                e = (E)items[index];
+            else
+                oobe = true;
+        } finally {
+            lock.unlockRead(stamp);
         }
+        if (oobe)
+            throw new ArrayIndexOutOfBoundsException(index);
+        return e;
     }
 
     public int hashCode() {
-        return internalHashCode(0, -1);
+        int h;
+        final StampedLock lock = this.lock;
+        long s = lock.readLock();
+        try {
+            h = internalHashCode(0, -1);
+        } finally {
+            lock.unlockRead(s);
+        }
+        return h;
     }
 
     public int indexOf(Object o) {
-        SequenceLock lock = this.lock;
-        long seq = lock.awaitAvailability();
-        Object[] items = array;
-        int n = count;
-        if (n <= items.length) {
-            boolean valid = true;
-            for (int i = 0; i < n; ++i) {
-                Object e = items[i];
-                if (lock.getSequence() == seq) {
-                    if (o == null? e == null : o.equals(e))
-                        return i;
-                }
-                else {
-                    valid = false;
-                    break;
-                }
-            }
-            if (valid)
-                return -1;
-        }
-        lock.lock();
+        int idx;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
         try {
-            return rawIndexOf(o, 0, count);
+            idx = findFirstIndex(array, o, 0, count);
         } finally {
-            lock.unlock();
+            lock.unlockRead(stamp);
         }
+        return idx;
     }
 
     public boolean isEmpty() {
-        long ignore = lock.getSequence();
-        return count == 0;
+        final StampedLock lock = this.lock;
+        long stamp = lock.tryOptimisticRead();
+        return count == 0; // no need for validation
     }
 
     public Iterator<E> iterator() {
-        return new Itr(this, 0);
+        return new Itr<E>(this, 0);
     }
 
     public int lastIndexOf(Object o) {
-        SequenceLock lock = this.lock;
-        long seq = lock.awaitAvailability();
-        Object[] items = array;
-        int n = count;
-        if (n <= items.length) {
-            int idx = validatedLastIndexOf(o, items, n - 1, 0, seq);
-            if (lock.getSequence() == seq)
-                return idx;
-        }
-        lock.lock();
+        int idx;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
         try {
-            return rawLastIndexOf(o, count - 1, 0);
+            idx = findLastIndex(array, o, count - 1, 0);
         } finally {
-            lock.unlock();
+            lock.unlockRead(stamp);
         }
+        return idx;
     }
 
     public ListIterator<E> listIterator() {
-        return new Itr(this, 0);
+        return new Itr<E>(this, 0);
     }
 
     public ListIterator<E> listIterator(int index) {
-        return new Itr(this, index);
+        return new Itr<E>(this, index);
     }
 
-    public E remove(int index) {
-        SequenceLock lock = this.lock;
-        Object oldValue;
-        lock.lock();
+    @SuppressWarnings("unchecked") public E remove(int index) {
+        E oldValue = null;
+        boolean oobe = false;
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
             if (index < 0 || index >= count)
-                throw new ArrayIndexOutOfBoundsException(index);
-            oldValue = array[index];
-            rawRemoveAt(index);
+                oobe = true;
+            else {
+                oldValue = (E) array[index];
+                rawRemoveAt(index);
+            }
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
-        return (E)oldValue;
+        if (oobe)
+            throw new ArrayIndexOutOfBoundsException(index);
+        return oldValue;
     }
 
     public boolean remove(Object o) {
-        SequenceLock lock = this.lock;
-        boolean removed;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            removed = rawRemoveAt(rawIndexOf(o, 0, count));
+            return rawRemoveAt(findFirstIndex(array, o, 0, count));
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
-        return removed;
     }
 
     public boolean removeAll(Collection<?> c) {
-        return internalRemoveAll(c, 0, -1);
+        return lockedRemoveAll(c, 0, -1);
     }
 
     public boolean retainAll(Collection<?> c) {
-        return internalRetainAll(c, 0, -1);
+        return lockedRetainAll(c, 0, -1);
     }
 
-    public E set(int index, E element) {
-        Object oldValue;
-        SequenceLock lock = this.lock;
-        lock.lock();
+    @SuppressWarnings("unchecked") public E set(int index, E element) {
+        E oldValue = null;
+        boolean oobe = false;
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            if (index < 0 || index >= count)
-                throw new ArrayIndexOutOfBoundsException(index);
-            oldValue = array[index];
-            array[index] = element;
+            Object[] items = array;
+            if (items == null || index < 0 || index >= count)
+                oobe = true;
+            else {
+                oldValue = (E) items[index];
+                items[index] = element;
+            }
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
-        return (E)oldValue;
+        if (oobe)
+            throw new ArrayIndexOutOfBoundsException(index);
+        return oldValue;
     }
 
     public int size() {
-        long ignore = lock.getSequence();
-        return count;
+        final StampedLock lock = this.lock;
+        long stamp = lock.tryOptimisticRead();
+        return count; // no need for validation
+    }
+
+    private int lockedSize() {
+        int n;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            n = count;
+        } finally {
+            lock.unlockRead(stamp);
+        }
+        return n;
     }
 
     public List<E> subList(int fromIndex, int toIndex) {
-        int c = size();
         int ssize = toIndex - fromIndex;
-        if (fromIndex < 0 || toIndex > c || ssize < 0)
-            throw new IndexOutOfBoundsException();
-        return new ReadMostlyVectorSublist(this, fromIndex, ssize);
+        if (ssize >= 0 && fromIndex >= 0) {
+            ReadMostlyVectorSublist<E> ret = null;
+            final StampedLock lock = this.lock;
+            long stamp = lock.readLock();
+            try {
+                if (toIndex <= count)
+                    ret = new ReadMostlyVectorSublist<E>(this, fromIndex, ssize);
+            } finally {
+                lock.unlockRead(stamp);
+            }
+            if (ret != null)
+                return ret;
+        }
+
+        throw new ArrayIndexOutOfBoundsException(fromIndex < 0 ? fromIndex : toIndex);
     }
 
     public Object[] toArray() {
-        return internalToArray(0, -1);
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            return internalToArray(0, -1);
+        } finally {
+            lock.unlockRead(stamp);
+        }
     }
 
     public <T> T[] toArray(T[] a) {
-        return internalToArray(a, 0, -1);
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            return internalToArray(a, 0, -1);
+        } finally {
+            lock.unlockRead(stamp);
+        }
     }
 
     public String toString() {
-        return internalToString(0, -1);
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            return internalToString(0, -1);
+        } finally {
+            lock.unlockRead(stamp);
+        }
     }
 
     // ReadMostlyVector-only methods
 
     /**
-     * Append the element if not present.
+     * Appends the element, if not present.
      *
      * @param e element to be added to this list, if absent
-     * @return <tt>true</tt> if the element was added
+     * @return {@code true} if the element was added
      */
     public boolean addIfAbsent(E e) {
-        boolean added;
-        SequenceLock lock = this.lock;
-        lock.lock();
+        boolean ret;
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            if (rawIndexOf(e, 0, count) < 0) {
+            if (findFirstIndex(array, e, 0, count) < 0) {
                 rawAdd(e);
-                added = true;
+                ret = true;
             }
             else
-                added = false;
+                ret = false;
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
-        return added;
+        return ret;
     }
 
     /**
@@ -834,138 +818,168 @@ public class ReadMostlyVector<E> impleme
         Object[] cs = c.toArray();
         int clen = cs.length;
         if (clen != 0) {
-            lock.lock();
+            long stamp = lock.writeLock();
             try {
                 for (int i = 0; i < clen; ++i) {
-                    Object e = cs[i];
-                    if (rawIndexOf(e, 0, count) < 0) {
+                    @SuppressWarnings("unchecked")
+                    E e = (E) cs[i];
+                    if (findFirstIndex(array, e, 0, count) < 0) {
                         rawAdd(e);
                         ++added;
                     }
                 }
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
         }
         return added;
     }
 
+    /**
+     * Returns an iterator operating over a snapshot copy of the
+     * elements of this collection created upon construction of the
+     * iterator. The iterator does <em>NOT</em> support the
+     * {@code remove} method.
+     *
+     * @return an iterator over the elements in this list in proper sequence
+     */
+    public Iterator<E> snapshotIterator() {
+        return new SnapshotIterator<E>(this);
+    }
+
+    static final class SnapshotIterator<E> implements Iterator<E> {
+        private final Object[] items;
+        private int cursor;
+        SnapshotIterator(ReadMostlyVector<E> v) { items = v.toArray(); }
+        public boolean hasNext() { return cursor < items.length; }
+        @SuppressWarnings("unchecked") public E next() {
+            if (cursor < items.length)
+                return (E) items[cursor++];
+            throw new NoSuchElementException();
+        }
+        public void remove() { throw new UnsupportedOperationException() ; }
+    }
+
+    /** Interface describing a void action of one argument */
+    public interface Action<A> { void apply(A a); }
+
+    public void forEachReadOnly(Action<E> action) {
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            Object[] items;
+            int len, n;
+            if ((items = array) != null && (len = items.length) > 0 &&
+                (n = count) <= len) {
+                for (int i = 0; i < n; ++i) {
+                    @SuppressWarnings("unchecked") E e = (E)items[i];
+                    action.apply(e);
+                }
+            }
+        } finally {
+            lock.unlockRead(stamp);
+        }
+    }
+
     // Vector-only methods
 
     /** See {@link Vector#firstElement} */
     public E firstElement() {
-        SequenceLock lock = this.lock;
-        for (;;) {
-            long seq = lock.awaitAvailability();
+        final StampedLock lock = this.lock;
+        long stamp = lock.tryOptimisticRead();
+        Object[] items;
+        if ((items = array) != null && count > 0 && items.length > 0) {
+            @SuppressWarnings("unchecked") E e = (E)items[0];
+            if (lock.validate(stamp))
+                return e;
+        }
+        return lockedFirstElement();
+    }
+
+    @SuppressWarnings("unchecked") private E lockedFirstElement() {
+        Object e = null;
+        boolean oobe = false;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
             Object[] items = array;
-            int len = items.length;
-            int n = count;
-            if (n > len)
-                continue;
-            Object e; boolean ex;
-            if (n > 0) {
+            if (items != null && count > 0 && items.length > 0)
                 e = items[0];
-                ex = false;
-            }
-            else {
-                e = null;
-                ex = true;
-            }
-            if (lock.getSequence() == seq) {
-                if (ex)
-                    throw new NoSuchElementException();
-                else
-                    return (E)e;
-            }
+            else
+                oobe = true;
+        } finally {
+            lock.unlockRead(stamp);
         }
+        if (oobe)
+            throw new NoSuchElementException();
+        return (E) e;
     }
 
     /** See {@link Vector#lastElement} */
     public E lastElement() {
-        SequenceLock lock = this.lock;
-        for (;;) {
-            long seq = lock.awaitAvailability();
+        final StampedLock lock = this.lock;
+        long stamp = lock.tryOptimisticRead();
+        Object[] items;
+        int i;
+        if ((items = array) != null && (i = count - 1) >= 0 &&
+            i < items.length) {
+            @SuppressWarnings("unchecked") E e = (E)items[i];
+            if (lock.validate(stamp))
+                return e;
+        }
+        return lockedLastElement();
+    }
+
+    @SuppressWarnings("unchecked") private E lockedLastElement() {
+        Object e = null;
+        boolean oobe = false;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
             Object[] items = array;
-            int len = items.length;
-            int n = count;
-            if (n > len)
-                continue;
-            Object e; boolean ex;
-            if (n > 0) {
-                e = items[n - 1];
-                ex = false;
-            }
-            else {
-                e = null;
-                ex = true;
-            }
-            if (lock.getSequence() == seq) {
-                if (ex)
-                    throw new NoSuchElementException();
-                else
-                    return (E)e;
-            }
+            int i = count - 1;
+            if (items != null && i >= 0 && i < items.length)
+                e = items[i];
+            else
+                oobe = true;
+        } finally {
+            lock.unlockRead(stamp);
         }
+        if (oobe)
+            throw new NoSuchElementException();
+        return (E) e;
     }
 
     /** See {@link Vector#indexOf(Object, int)} */
     public int indexOf(Object o, int index) {
-        SequenceLock lock = this.lock;
-        int idx = 0;
-        boolean ex = false;
-        long seq = lock.awaitAvailability();
-        Object[] items = array;
-        int n = count;
-        boolean retry = false;
-        if (n > items.length)
-            retry = true;
-        else if (index < 0)
-            ex = true;
-        else
-            idx = validatedIndexOf(o, items, index, n, seq);
-        if (retry || lock.getSequence() != seq) {
-            lock.lock();
-            try {
-                if (index < 0)
-                    ex = true;
-                else
-                    idx = rawIndexOf(o, 0, count);
-            } finally {
-                lock.unlock();
-            }
-        }
-        if (ex)
+        if (index < 0)
             throw new ArrayIndexOutOfBoundsException(index);
+        int idx;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            idx = findFirstIndex(array, o, index, count);
+        } finally {
+            lock.unlockRead(stamp);
+        }
         return idx;
     }
 
     /** See {@link Vector#lastIndexOf(Object, int)} */
     public int lastIndexOf(Object o, int index) {
-        SequenceLock lock = this.lock;
-        int idx = 0;
-        boolean ex = false;
-        long seq = lock.awaitAvailability();
-        Object[] items = array;
-        int n = count;
-        boolean retry = false;
-        if (n > items.length)
-            retry = true;
-        else if (index >= n)
-            ex = true;
-        else
-            idx = validatedLastIndexOf(o, items, index, 0, seq);
-        if (retry || lock.getSequence() != seq) {
-            lock.lock();
-            try {
-                if (index >= count)
-                    ex = true;
-                else
-                    idx = rawLastIndexOf(o, index, 0);
-            } finally {
-                lock.unlock();
-            }
+        boolean oobe = false;
+        int idx = -1;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            if (index < count)
+                idx = findLastIndex(array, o, index, 0);
+            else
+                oobe = true;
+        } finally {
+            lock.unlockRead(stamp);
         }
-        if (ex)
+        if (oobe)
             throw new ArrayIndexOutOfBoundsException(index);
         return idx;
     }
@@ -974,67 +988,73 @@ public class ReadMostlyVector<E> impleme
     public void setSize(int newSize) {
         if (newSize < 0)
             throw new ArrayIndexOutOfBoundsException(newSize);
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
+            Object[] items;
             int n = count;
             if (newSize > n)
                 grow(newSize);
-            else {
+            else if ((items = array) != null) {
                 for (int i = newSize ; i < n ; i++)
-                    array[i] = null;
+                    items[i] = null;
             }
             count = newSize;
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
     }
 
     /** See {@link Vector#copyInto} */
     public void copyInto(Object[] anArray) {
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            System.arraycopy(array, 0, anArray, 0, count);
+            Object[] items;
+            if ((items = array) != null)
+                System.arraycopy(items, 0, anArray, 0, count);
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
     }
 
     /** See {@link Vector#trimToSize} */
     public void trimToSize() {
-        SequenceLock lock = this.lock;
-        lock.lock();
+        final StampedLock lock = this.lock;
+        long stamp = lock.writeLock();
         try {
-            if (count < array.length)
-                array = Arrays.copyOf(array, count);
+            Object[] items = array;
+            int n = count;
+            if (items != null && n < items.length)
+                array = Arrays.copyOf(items, n);
         } finally {
-            lock.unlock();
+            lock.unlockWrite(stamp);
         }
     }
 
     /** See {@link Vector#ensureCapacity} */
     public void ensureCapacity(int minCapacity) {
         if (minCapacity > 0) {
-            SequenceLock lock = this.lock;
-            lock.lock();
+            final StampedLock lock = this.lock;
+            long stamp = lock.writeLock();
             try {
-                if (minCapacity - array.length > 0)
+                Object[] items = array;
+                int cap = (items == null) ? 0 : items.length;
+                if (minCapacity - cap > 0)
                     grow(minCapacity);
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
         }
     }
 
     /** See {@link Vector#elements} */
     public Enumeration<E> elements() {
-        return new Itr(this, 0);
+        return new Itr<E>(this, 0);
     }
 
     /** See {@link Vector#capacity} */
     public int capacity() {
-        long ignore = lock.getSequence();
         return array.length;
     }
 
@@ -1075,182 +1095,167 @@ public class ReadMostlyVector<E> impleme
 
     // other methods
 
-    public Object clone() {
-        SequenceLock lock = this.lock;
+    public ReadMostlyVector<E> clone() {
         Object[] a = null;
-        boolean retry = false;
-        long seq = lock.awaitAvailability();
-        Object[] items = array;
-        int n = count;
-        if (n <= items.length)
-            a = Arrays.copyOf(items, n);
-        else
-            retry = true;
-        if (retry || lock.getSequence() != seq) {
-            lock.lock();
-            try {
-                n = count;
-                a = Arrays.copyOf(array, n);
-            } finally {
-                lock.unlock();
+        int n;
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
+        try {
+            Object[] items = array;
+            if (items == null)
+                n = 0;
+            else {
+                int len = items.length;
+                if ((n = count) > len)
+                    n = len;
+                a = Arrays.copyOf(items, n);
             }
+        } finally {
+            lock.unlockRead(stamp);
         }
-        return new ReadMostlyVector(a, n, capacityIncrement);
+        return new ReadMostlyVector<E>(a, n, capacityIncrement);
     }
 
     private void writeObject(java.io.ObjectOutputStream s)
-            throws java.io.IOException {
-        SequenceLock lock = this.lock;
-        lock.lock();
+        throws java.io.IOException {
+        final StampedLock lock = this.lock;
+        long stamp = lock.readLock();
         try {
             s.defaultWriteObject();
         } finally {
-            lock.unlock();
+            lock.unlockRead(stamp);
         }
     }
 
-    static final class Itr<E> implements ListIterator<E>, Enumeration<E>  {
+    static final class Itr<E> implements ListIterator<E>, Enumeration<E> {
+        final StampedLock lock;
         final ReadMostlyVector<E> list;
-        final SequenceLock lock;
         Object[] items;
-        Object next, prev;
         long seq;
         int cursor;
         int fence;
         int lastRet;
-        boolean validNext, validPrev;
 
         Itr(ReadMostlyVector<E> list, int index) {
-            this.list = list;
-            this.lock = list.lock;
-            this.cursor = index;
-            this.lastRet = -1;
-            refresh();
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                this.list = list;
+                this.lock = lock;
+                this.items = list.array;
+                this.fence = list.count;
+                this.cursor = index;
+                this.lastRet = -1;
+            } finally {
+                this.seq = lock.tryConvertToOptimisticRead(stamp);
+            }
             if (index < 0 || index > fence)
                 throw new ArrayIndexOutOfBoundsException(index);
         }
 
-        private void refresh() {
-            validNext = validPrev = false;
-            do {
-                seq = lock.awaitAvailability();
-                items = list.array;
-            } while ((fence = list.count) > items.length ||
-                     lock.getSequence() != seq);
+        public boolean hasPrevious() {
+            return cursor > 0;
         }
 
-        public boolean hasNext() {
-            boolean valid;
-            int i = cursor;
-            for (;;) {
-                if (i >= fence || i < 0 || i >= items.length) {
-                    valid = false;
-                    break;
-                }
-                next = items[i];
-                if (lock.getSequence() == seq) {
-                    valid = true;
-                    break;
-                }
-                refresh();
-            }
-            return validNext = valid;
+        public int nextIndex() {
+            return cursor;
         }
 
-        public boolean hasPrevious() {
-            boolean valid;
-            int i = cursor - 1;
-            for (;;) {
-                if (i >= fence || i < 0 || i >= items.length) {
-                    valid = false;
-                    break;
-                }
-                prev = items[i];
-                if (lock.getSequence() == seq) {
-                    valid = true;
-                    break;
-                }
-                refresh();
-            }
-            return validPrev = valid;
+        public int previousIndex() {
+            return cursor - 1;
+        }
+
+        public boolean hasNext() {
+            return cursor < fence;
         }
 
         public E next() {
-            if (validNext || hasNext()) {
-                validNext = false;
-                lastRet = cursor++;
-                return (E) next;
-            }
-            throw new NoSuchElementException();
+            int i = cursor;
+            Object[] es = items;
+            if (es == null || i < 0 || i >= fence || i >= es.length)
+                throw new NoSuchElementException();
+            @SuppressWarnings("unchecked") E e = (E)es[i];
+            lastRet = i;
+            cursor = i + 1;
+            if (!lock.validate(seq))
+                throw new ConcurrentModificationException();
+            return e;
         }
 
         public E previous() {
-            if (validPrev || hasPrevious()) {
-                validPrev = false;
-                lastRet = cursor--;
-                return (E) prev;
-            }
-            throw new NoSuchElementException();
+            int i = cursor - 1;
+            Object[] es = items;
+            if (es == null || i < 0 || i >= fence || i >= es.length)
+                throw new NoSuchElementException();
+            @SuppressWarnings("unchecked") E e = (E)es[i];
+            lastRet = i;
+            cursor = i;
+            if (!lock.validate(seq))
+                throw new ConcurrentModificationException();
+            return e;
         }
 
         public void remove() {
             int i = lastRet;
             if (i < 0)
                 throw new IllegalStateException();
-            lock.lock();
+            if ((seq = lock.tryConvertToWriteLock(seq)) == 0)
+                throw new ConcurrentModificationException();
             try {
-                if (i < list.count)
-                    list.remove(i);
+                list.rawRemoveAt(i);
+                fence = list.count;
+                cursor = i;
+                lastRet = -1;
             } finally {
-                lock.unlock();
+                seq = lock.tryConvertToOptimisticRead(seq);
             }
-            cursor = i;
-            lastRet = -1;
-            refresh();
         }
 
         public void set(E e) {
             int i = lastRet;
-            if (i < 0)
+            Object[] es = items;
+            if (es == null || i < 0 | i >= fence)
                 throw new IllegalStateException();
-            lock.lock();
+            if ((seq = lock.tryConvertToWriteLock(seq)) == 0)
+                throw new ConcurrentModificationException();
             try {
-                if (i < list.count)
-                    list.set(i, e);
+                es[i] = e;
             } finally {
-                lock.unlock();
+                seq = lock.tryConvertToOptimisticRead(seq);
             }
-            refresh();
         }
 
         public void add(E e) {
             int i = cursor;
             if (i < 0)
                 throw new IllegalStateException();
-            lock.lock();
+            if ((seq = lock.tryConvertToWriteLock(seq)) == 0)
+                throw new ConcurrentModificationException();
             try {
-                if (i <= list.count)
-                    list.add(i, e);
+                list.rawAddAt(i, e);
+                items = list.array;
+                fence = list.count;
+                cursor = i + 1;
+                lastRet = -1;
             } finally {
-                lock.unlock();
+                seq = lock.tryConvertToOptimisticRead(seq);
             }
-            cursor = i + 1;
-            lastRet = -1;
-            refresh();
         }
 
         public boolean hasMoreElements() { return hasNext(); }
         public E nextElement() { return next(); }
-        public int nextIndex() { return cursor; }
-        public int previousIndex() { return cursor - 1; }
     }
 
-    static final class ReadMostlyVectorSublist<E> implements List<E>, RandomAccess, java.io.Serializable {
+    static final class ReadMostlyVectorSublist<E>
+            implements List<E>, RandomAccess, java.io.Serializable {
+        private static final long serialVersionUID = 3041673470172026059L;
+
         final ReadMostlyVector<E> list;
         final int offset;
         volatile int size;
 
-        ReadMostlyVectorSublist(ReadMostlyVector<E> list, int offset, int size) {
+        ReadMostlyVectorSublist(ReadMostlyVector<E> list,
+                                int offset, int size) {
             this.list = list;
             this.offset = offset;
             this.size = size;
@@ -1262,75 +1267,73 @@ public class ReadMostlyVector<E> impleme
         }
 
         public boolean add(E element) {
-            SequenceLock lock = list.lock;
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
             try {
                 int c = size;
                 list.rawAddAt(c + offset, element);
                 size = c + 1;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
             return true;
         }
 
         public void add(int index, E element) {
-            SequenceLock lock = list.lock;
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
             try {
                 if (index < 0 || index > size)
                     throw new ArrayIndexOutOfBoundsException(index);
                 list.rawAddAt(index + offset, element);
                 ++size;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
         }
 
         public boolean addAll(Collection<? extends E> c) {
             Object[] elements = c.toArray();
-            int added;
-            SequenceLock lock = list.lock;
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
             try {
                 int s = size;
                 int pc = list.count;
                 list.rawAddAllAt(offset + s, elements);
-                added = list.count - pc;
+                int added = list.count - pc;
                 size = s + added;
+                return added != 0;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
-            return added != 0;
         }
 
         public boolean addAll(int index, Collection<? extends E> c) {
             Object[] elements = c.toArray();
-            int added;
-            SequenceLock lock = list.lock;
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
             try {
                 int s = size;
                 if (index < 0 || index > s)
                     throw new ArrayIndexOutOfBoundsException(index);
                 int pc = list.count;
                 list.rawAddAllAt(index + offset, elements);
-                added = list.count - pc;
+                int added = list.count - pc;
                 size = s + added;
+                return added != 0;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
-            return added != 0;
         }
 
         public void clear() {
-            SequenceLock lock = list.lock;
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
             try {
                 list.internalClear(offset, offset + size);
                 size = 0;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
         }
 
@@ -1339,7 +1342,13 @@ public class ReadMostlyVector<E> impleme
         }
 
         public boolean containsAll(Collection<?> c) {
-            return list.internalContainsAll(c, offset, offset + size);
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                return list.internalContainsAll(c, offset, offset + size);
+            } finally {
+                lock.unlockRead(stamp);
+            }
         }
 
         public boolean equals(Object o) {
@@ -1347,7 +1356,13 @@ public class ReadMostlyVector<E> impleme
                 return true;
             if (!(o instanceof List))
                 return false;
-            return list.internalEquals((List<?>)(o), offset, offset + size);
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                return list.internalEquals((List<?>)(o), offset, offset + size);
+            } finally {
+                lock.unlockRead(stamp);
+            }
         }
 
         public E get(int index) {
@@ -1357,105 +1372,92 @@ public class ReadMostlyVector<E> impleme
         }
 
         public int hashCode() {
-            return list.internalHashCode(offset, offset + size);
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                return list.internalHashCode(offset, offset + size);
+            } finally {
+                lock.unlockRead(stamp);
+            }
         }
 
         public int indexOf(Object o) {
-            SequenceLock lock = list.lock;
-            long seq = lock.awaitAvailability();
-            Object[] items = list.array;
-            int c = list.count;
-            if (c <= items.length) {
-                int idx = list.validatedIndexOf(o, items, offset,
-                                                offset + size, seq);
-                if (lock.getSequence() == seq)
-                    return idx < 0 ? -1 : idx - offset;
-            }
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
             try {
-                int idx = list.rawIndexOf(o, offset, offset + size);
+                int idx = findFirstIndex(list.array, o, offset, offset + size);
                 return idx < 0 ? -1 : idx - offset;
             } finally {
-                lock.unlock();
+                lock.unlockRead(stamp);
             }
         }
 
         public boolean isEmpty() {
-            return size == 0;
+            return size() == 0;
         }
 
         public Iterator<E> iterator() {
-            return new SubItr(this, offset);
+            return new SubItr<E>(this, offset);
         }
 
         public int lastIndexOf(Object o) {
-            SequenceLock lock = list.lock;
-            long seq = lock.awaitAvailability();
-            Object[] items = list.array;
-            int c = list.count;
-            if (c <= items.length) {
-                int idx = list.validatedLastIndexOf(o, items, offset+size-1,
-                                                    offset, seq);
-                if (lock.getSequence() == seq)
-                    return idx < 0 ? -1 : idx - offset;
-            }
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
             try {
-                int idx = list.rawLastIndexOf(o, offset + size - 1, offset);
+                int idx = findLastIndex(list.array, o, offset + size - 1, offset);
                 return idx < 0 ? -1 : idx - offset;
             } finally {
-                lock.unlock();
+                lock.unlockRead(stamp);
             }
         }
 
         public ListIterator<E> listIterator() {
-            return new SubItr(this, offset);
+            return new SubItr<E>(this, offset);
         }
 
         public ListIterator<E> listIterator(int index) {
-            return new SubItr(this, index + offset);
+            return new SubItr<E>(this, index + offset);
         }
 
         public E remove(int index) {
-            Object result;
-            SequenceLock lock = list.lock;
-            lock.lock();
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
             try {
                 Object[] items = list.array;
                 int i = index + offset;
-                if (index < 0 || index >= size || i >= items.length)
+                if (items == null || index < 0 || index >= size || i >= items.length)
                     throw new ArrayIndexOutOfBoundsException(index);
-                result = items[i];
+                @SuppressWarnings("unchecked") E result = (E)items[i];
                 list.rawRemoveAt(i);
                 size--;
+                return result;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
-            return (E)result;
         }
 
         public boolean remove(Object o) {
-            boolean removed = false;
-            SequenceLock lock = list.lock;
-            lock.lock();
-            try {
-                if (list.rawRemoveAt(list.rawIndexOf(o, offset,
-                                                     offset + size))) {
-                    removed = true;
+            final StampedLock lock = list.lock;
+            long stamp = lock.writeLock();
+            try {
+                if (list.rawRemoveAt(findFirstIndex(list.array, o, offset,
+                                                    offset + size))) {
                     --size;
+                    return true;
                 }
+                else
+                    return false;
             } finally {
-                lock.unlock();
+                lock.unlockWrite(stamp);
             }
-            return removed;
         }
 
         public boolean removeAll(Collection<?> c) {
-            return list.internalRemoveAll(c, offset, offset + size);
+            return list.lockedRemoveAll(c, offset, offset + size);
         }
 
         public boolean retainAll(Collection<?> c) {
-            return list.internalRetainAll(c, offset, offset + size);
+            return list.lockedRetainAll(c, offset, offset + size);
         }
 
         public E set(int index, E element) {
@@ -1471,21 +1473,41 @@ public class ReadMostlyVector<E> impleme
         public List<E> subList(int fromIndex, int toIndex) {
             int c = size;
             int ssize = toIndex - fromIndex;
-            if (fromIndex < 0 || toIndex > c || ssize < 0)
-                throw new IndexOutOfBoundsException();
-            return new ReadMostlyVectorSublist(list, offset+fromIndex, ssize);
+            if (fromIndex < 0)
+                throw new ArrayIndexOutOfBoundsException(fromIndex);
+            if (toIndex > c || ssize < 0)
+                throw new ArrayIndexOutOfBoundsException(toIndex);
+            return new ReadMostlyVectorSublist<E>(list, offset+fromIndex, ssize);
         }
 
         public Object[] toArray() {
-            return list.internalToArray(offset, offset + size);
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                return list.internalToArray(offset, offset + size);
+            } finally {
+                lock.unlockRead(stamp);
+            }
         }
 
         public <T> T[] toArray(T[] a) {
-            return list.internalToArray(a, offset, offset + size);
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                return list.internalToArray(a, offset, offset + size);
+            } finally {
+                lock.unlockRead(stamp);
+            }
         }
 
         public String toString() {
-            return list.internalToString(offset, offset + size);
+            final StampedLock lock = list.lock;
+            long stamp = lock.readLock();
+            try {
+                return list.internalToString(offset, offset + size);
+            } finally {
+                lock.unlockRead(stamp);
+            }
         }
 
     }
@@ -1493,151 +1515,118 @@ public class ReadMostlyVector<E> impleme
     static final class SubItr<E> implements ListIterator<E> {
         final ReadMostlyVectorSublist<E> sublist;
         final ReadMostlyVector<E> list;
-        final SequenceLock lock;
+        final StampedLock lock;
         Object[] items;
-        Object next, prev;
         long seq;
         int cursor;
+        int origin;
         int fence;
         int lastRet;
-        boolean validNext, validPrev;
 
         SubItr(ReadMostlyVectorSublist<E> sublist, int index) {
-            this.sublist = sublist;
-            this.list = sublist.list;
-            this.lock = list.lock;
-            this.cursor = index;
-            this.lastRet = -1;
-            refresh();
-            if (index < 0 || index > fence)
+            final StampedLock lock = sublist.list.lock;
+            long stamp = lock.readLock();
+            try {
+                this.sublist = sublist;
+                this.list = sublist.list;
+                this.lock = lock;
+                this.cursor = index;
+                this.origin = sublist.offset;
+                this.fence = origin + sublist.size;
+                this.lastRet = -1;
+            } finally {
+                this.seq = lock.tryConvertToOptimisticRead(stamp);
+            }
+            if (index < 0 || cursor > fence)
                 throw new ArrayIndexOutOfBoundsException(index);
         }
 
-        private void refresh() {
-            validNext = validPrev = false;
-            do {
-                int n;
-                seq = lock.awaitAvailability();
-                items = list.array;
-                if ((n = list.count) > items.length)
-                    continue;
-                int b = sublist.offset + sublist.size;
-                fence = b < n ? b : n;
-            } while (lock.getSequence() != seq);
+        public int nextIndex() {
+            return cursor - origin;
+        }
+
+        public int previousIndex() {
+            return cursor - origin - 1;
         }
 
         public boolean hasNext() {
-            boolean valid;
-            int i = cursor;
-            for (;;) {
-                if (i >= fence || i < 0 || i >= items.length) {
-                    valid = false;
-                    break;
-                }
-                next = items[i];
-                if (lock.getSequence() == seq) {
-                    valid = true;
-                    break;
-                }
-                refresh();
-            }
-            return validNext = valid;
+            return cursor < fence;
         }
 
         public boolean hasPrevious() {
-            boolean valid;
-            int i = cursor - 1;
-            for (;;) {
-                if (i >= fence || i < 0 || i >= items.length) {
-                    valid = false;
-                    break;
-                }
-                prev = items[i];
-                if (lock.getSequence() == seq) {
-                    valid = true;
-                    break;
-                }
-                refresh();
-            }
-            return validPrev = valid;
+            return cursor > origin;
         }
 
         public E next() {
-            if (validNext || hasNext()) {
-                validNext = false;
-                lastRet = cursor++;
-                return (E) next;
-            }
-            throw new NoSuchElementException();
+            int i = cursor;
+            Object[] es = items;
+            if (es == null || i < origin || i >= fence || i >= es.length)
+                throw new NoSuchElementException();
+            @SuppressWarnings("unchecked") E e = (E)es[i];
+            lastRet = i;
+            cursor = i + 1;
+            if (!lock.validate(seq))
+                throw new ConcurrentModificationException();
+            return e;
         }
 
         public E previous() {
-            if (validPrev || hasPrevious()) {
-                validPrev = false;
-                lastRet = cursor--;
-                return (E) prev;
-            }
-            throw new NoSuchElementException();
-        }
-
-        public int nextIndex() {
-            return cursor - sublist.offset;
-        }
-
-        public int previousIndex() {
-            return cursor - 1 - sublist.offset;
+            int i = cursor - 1;
+            Object[] es = items;
+            if (es == null || i < 0 || i >= fence || i >= es.length)
+                throw new NoSuchElementException();
+            @SuppressWarnings("unchecked") E e = (E)es[i];
+            lastRet = i;
+            cursor = i;
+            if (!lock.validate(seq))
+                throw new ConcurrentModificationException();
+            return e;
         }
 
         public void remove() {
             int i = lastRet;
             if (i < 0)
                 throw new IllegalStateException();
-            cursor = i;
-            lastRet = -1;
-            lock.lock();
+            if ((seq = lock.tryConvertToWriteLock(seq)) == 0)
+                throw new ConcurrentModificationException();
             try {
-                if (i < list.count) {
-                    list.remove(i);
-                    --sublist.size;
-                }
+                list.rawRemoveAt(i);
+                fence = origin + sublist.size;
+                cursor = i;
+                lastRet = -1;
             } finally {
-                lock.unlock();
+                seq = lock.tryConvertToOptimisticRead(seq);
             }
-            refresh();
         }
 
         public void set(E e) {
             int i = lastRet;
-            if (i < 0)
+            if (i < origin || i >= fence)
                 throw new IllegalStateException();
-            lock.lock();
+            if ((seq = lock.tryConvertToWriteLock(seq)) == 0)
+                throw new ConcurrentModificationException();
             try {
-                if (i < list.count)
-                    list.set(i, e);
+                list.set(i, e);
             } finally {
-                lock.unlock();
+                seq = lock.tryConvertToOptimisticRead(seq);
             }
-            refresh();
         }
 
         public void add(E e) {
             int i = cursor;
-            if (i < 0)
+            if (i < origin || i >= fence)
                 throw new IllegalStateException();
-            cursor = i + 1;
-            lastRet = -1;
-            lock.lock();
+            if ((seq = lock.tryConvertToWriteLock(seq)) == 0)
+                throw new ConcurrentModificationException();
             try {
-                if (i <= list.count) {
-                    list.add(i, e);
-                    ++sublist.size;
-                }
+                list.rawAddAt(i, e);
+                items = list.array;
+                fence = origin + sublist.size;
+                cursor = i + 1;
+                lastRet = -1;
             } finally {
-                lock.unlock();
+                seq = lock.tryConvertToOptimisticRead(seq);
             }
-            refresh();
         }
-
     }
 }
-