--- a/src/share/classes/java/util/IdentityHashMap.java	Thu Nov 23 19:33:26 2017 +0000
+++ b/src/share/classes/java/util/IdentityHashMap.java	Thu Nov 23 19:50:37 2017 +0000
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -24,7 +24,6 @@
  */
 
 package java.util;
-import java.io.*;
 
 /**
  * This class implements the <tt>Map</tt> interface with a hash table, using
@@ -69,7 +68,7 @@
  * maximum size and the number of buckets is unspecified.
  *
  * <p>If the size of the map (the number of key-value mappings) sufficiently
- * exceeds the expected maximum size, the number of buckets is increased
+ * exceeds the expected maximum size, the number of buckets is increased.
  * Increasing the number of buckets ("rehashing") may be fairly expensive, so
  * it pays to create identity hash maps with a sufficiently large expected
  * maximum size.  On the other hand, iteration over collection views requires
@@ -155,6 +154,10 @@
      * The maximum capacity, used if a higher value is implicitly specified
      * by either of the constructors with arguments.
      * MUST be a power of two <= 1<<29.
+     *
+     * In fact, the map can hold no more than MAXIMUM_CAPACITY-1 items
+     * because it has to have at least one slot with the key == null
+     * in order to avoid infinite loops in get(), put(), remove()
      */
     private static final int MAXIMUM_CAPACITY = 1 << 29;
 
@@ -176,11 +179,6 @@
     private transient int modCount;
 
     /**
-     * The next size value at which to resize (capacity * load factor).
-     */
-    private transient int threshold;
-
-    /**
      * Value representing null keys inside tables.
      */
     private static final Object NULL_KEY = new Object();
@@ -224,27 +222,18 @@
     }
 
     /**
-     * Returns the appropriate capacity for the specified expected maximum
-     * size.  Returns the smallest power of two between MINIMUM_CAPACITY
-     * and MAXIMUM_CAPACITY, inclusive, that is greater than
-     * (3 * expectedMaxSize)/2, if such a number exists.  Otherwise
-     * returns MAXIMUM_CAPACITY.  If (3 * expectedMaxSize)/2 is negative, it
-     * is assumed that overflow has occurred, and MAXIMUM_CAPACITY is returned.
+     * Returns the appropriate capacity for the given expected maximum size.
+     * Returns the smallest power of two between MINIMUM_CAPACITY and
+     * MAXIMUM_CAPACITY, inclusive, that is greater than (3 *
+     * expectedMaxSize)/2, if such a number exists.  Otherwise returns
+     * MAXIMUM_CAPACITY.
      */
-    private int capacity(int expectedMaxSize) {
-        // Compute min capacity for expectedMaxSize given a load factor of 2/3
-        int minCapacity = (3 * expectedMaxSize)/2;
-
-        // Compute the appropriate capacity
-        int result;
-        if (minCapacity > MAXIMUM_CAPACITY || minCapacity < 0) {
-            result = MAXIMUM_CAPACITY;
-        } else {
-            result = MINIMUM_CAPACITY;
-            while (result < minCapacity)
-                result <<= 1;
-        }
-        return result;
+    private static int capacity(int expectedMaxSize) {
+        // assert expectedMaxSize >= 0;
+        return
+            (expectedMaxSize > MAXIMUM_CAPACITY / 3) ? MAXIMUM_CAPACITY :
+            (expectedMaxSize <= 2 * MINIMUM_CAPACITY / 3) ? MINIMUM_CAPACITY :
+            Integer.highestOneBit(expectedMaxSize + (expectedMaxSize << 1));
     }
 
     /**
@@ -257,7 +246,6 @@
         // assert initCapacity >= MINIMUM_CAPACITY;
         // assert initCapacity <= MAXIMUM_CAPACITY;
 
-        threshold = (initCapacity * 2)/3;
         table = new Object[2 * initCapacity];
     }
 
@@ -423,51 +411,58 @@
      * @see     #containsKey(Object)
      */
     public V put(K key, V value) {
-        Object k = maskNull(key);
-        Object[] tab = table;
-        int len = tab.length;
-        int i = hash(k, len);
+        final Object k = maskNull(key);
+
+        retryAfterResize: for (;;) {
+            final Object[] tab = table;
+            final int len = tab.length;
+            int i = hash(k, len);
 
-        Object item;
-        while ( (item = tab[i]) != null) {
-            if (item == k) {
-                V oldValue = (V) tab[i + 1];
-                tab[i + 1] = value;
-                return oldValue;
+            for (Object item; (item = tab[i]) != null;
+                 i = nextKeyIndex(i, len)) {
+                if (item == k) {
+                    @SuppressWarnings("unchecked")
+                        V oldValue = (V) tab[i + 1];
+                    tab[i + 1] = value;
+                    return oldValue;
+                }
             }
-            i = nextKeyIndex(i, len);
-        }
+
+            final int s = size + 1;
+            // Use optimized form of 3 * s.
+            // Next capacity is len, 2 * current capacity.
+            if (s + (s << 1) > len && resize(len))
+                continue retryAfterResize;
 
-        modCount++;
-        tab[i] = k;
-        tab[i + 1] = value;
-        if (++size >= threshold)
-            resize(len); // len == 2 * current capacity.
-        return null;
+            modCount++;
+            tab[i] = k;
+            tab[i + 1] = value;
+            size = s;
+            return null;
+        }
     }
 
     /**
-     * Resize the table to hold given capacity.
+     * Resizes the table if necessary to hold given capacity.
      *
      * @param newCapacity the new capacity, must be a power of two.
+     * @return whether a resize did in fact take place
      */
-    private void resize(int newCapacity) {
+    private boolean resize(int newCapacity) {
         // assert (newCapacity & -newCapacity) == newCapacity; // power of 2
         int newLength = newCapacity * 2;
 
         Object[] oldTable = table;
         int oldLength = oldTable.length;
-        if (oldLength == 2*MAXIMUM_CAPACITY) { // can't expand any further
-            if (threshold == MAXIMUM_CAPACITY-1)
+        if (oldLength == 2 * MAXIMUM_CAPACITY) { // can't expand any further
+            if (size == MAXIMUM_CAPACITY - 1)
                 throw new IllegalStateException("Capacity exhausted.");
-            threshold = MAXIMUM_CAPACITY-1;  // Gigantic map!
-            return;
+            return false;
         }
         if (oldLength >= newLength)
-            return;
+            return false;
 
         Object[] newTable = new Object[newLength];
-        threshold = newLength / 3;
 
         for (int j = 0; j < oldLength; j += 2) {
             Object key = oldTable[j];
@@ -483,6 +478,7 @@
             }
         }
         table = newTable;
+        return true;
     }
 
     /**
@@ -497,8 +493,8 @@
         int n = m.size();
         if (n == 0)
             return;
-        if (n > threshold) // conservatively pre-expand
-            resize(capacity(n));
+        if (n > size)
+            resize(capacity(n)); // conservatively pre-expand
 
         for (Entry<? extends K, ? extends V> e : m.entrySet())
             put(e.getKey(), e.getValue());
@@ -534,7 +530,6 @@
                 return null;
             i = nextKeyIndex(i, len);
         }
-
     }
 
     /**
@@ -1168,8 +1163,8 @@
     private static final long serialVersionUID = 8188218128353913216L;
 
     /**
-     * Save the state of the <tt>IdentityHashMap</tt> instance to a stream
-     * (i.e., serialize it).
+     * Saves the state of the <tt>IdentityHashMap</tt> instance to a stream
+     * (i.e., serializes it).
      *
      * @serialData The <i>size</i> of the HashMap (the number of key-value
      *          mappings) (<tt>int</tt>), followed by the key (Object) and
@@ -1197,8 +1192,8 @@
     }
 
     /**
-     * Reconstitute the <tt>IdentityHashMap</tt> instance from a stream (i.e.,
-     * deserialize it).
+     * Reconstitutes the <tt>IdentityHashMap</tt> instance from a stream (i.e.,
+     * deserializes it).
      */
     private void readObject(java.io.ObjectInputStream s)
         throws java.io.IOException, ClassNotFoundException  {
@@ -1207,9 +1202,10 @@
 
         // Read in size (number of Mappings)
         int size = s.readInt();
-
-        // Allow for 33% growth (i.e., capacity is >= 2* size()).
-        init(capacity((size*4)/3));
+        if (size < 0)
+            throw new java.io.StreamCorruptedException
+                ("Illegal mappings count: " + size);
+        init(capacity(size));
 
         // Read the keys and values, and put the mappings in the table
         for (int i=0; i<size; i++) {
@@ -1224,7 +1220,7 @@
      * update modCount, etc.
      */
     private void putForCreate(K key, V value)
-        throws IOException
+        throws java.io.StreamCorruptedException
     {
         K k = (K)maskNull(key);
         Object[] tab = table;

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/java/util/IdentityHashMap/Capacity.java	Thu Nov 23 19:50:37 2017 +0000
@@ -0,0 +1,226 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Random;
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.*;
+
+/*
+ * @test
+ * @bug 6904367
+ * @summary IdentityHashMap reallocates storage when inserting expected
+ *          number of elements
+ * @run testng Capacity
+ */
+
+@Test
+public class Capacity {
+    static final Field tableField;
+    static final Random random = new Random();
+    static final Object[][] sizesData;
+
+    @DataProvider(name="sizes", parallel = true)
+    public Object[][] sizesToTest() { return sizesData; }
+
+    static {
+        try {
+            tableField = IdentityHashMap.class.getDeclaredField("table");
+            tableField.setAccessible(true);
+        } catch (NoSuchFieldException e) {
+            throw new LinkageError("table", e);
+        }
+
+        ArrayList<Object[]> sizes = new ArrayList<>();
+        for (int size = 0; size < 200; size++)
+            sizes.add(new Object[] { size });
+
+        // some numbers known to demonstrate bug 6904367
+        for (int size : new int[] {682, 683, 1365, 2730, 2731, 5461})
+            sizes.add(new Object[] { size });
+
+        // a few more random sizes to try
+        for (int i = 0; i != 128; i++)
+            sizes.add(new Object[] { random.nextInt(5000) });
+
+        sizesData = sizes.toArray(new Object[0][]);
+    }
+
+    static int capacity(IdentityHashMap<?,?> map) {
+        try {
+            return ((Object[]) tableField.get(map)).length / 2;
+        } catch (Throwable t) {
+            throw new LinkageError("table", t);
+        }
+    }
+
+    static void assertCapacity(IdentityHashMap<?,?> map,
+                               int expectedCapacity) {
+        assertEquals(capacity(map), expectedCapacity);
+    }
+
+    static void growUsingPut(IdentityHashMap<Object,Object> map,
+                             int elementsToAdd) {
+        for (int i = 0; i < elementsToAdd; i++)
+            map.put(new Object(), new Object());
+    }
+
+    static void growUsingPutAll(IdentityHashMap<Object,Object> map,
+                                int elementsToAdd) {
+        IdentityHashMap<Object,Object> other = new IdentityHashMap<>();
+        growUsingPut(other, elementsToAdd);
+        map.putAll(other);
+    }
+
+    static void growUsingRepeatedPutAll(IdentityHashMap<Object,Object> map,
+                                        int elementsToAdd) {
+        for (int i = 0; i < elementsToAdd; i++)
+            map.putAll(Collections.singletonMap(new Object(),
+                                                new Object()));
+    }
+
+    /**
+     * Checks that expected number of items can be inserted into
+     * the map without resizing of the internal storage
+     */
+    @Test(dataProvider = "sizes")
+    public void canInsertExpectedItemsWithoutResizing(int size)
+        throws Throwable {
+        // First try growing using put()
+        IdentityHashMap<Object,Object> m = new IdentityHashMap<>(size);
+        int initialCapacity = capacity(m);
+        growUsingPut(m, size);
+        assertCapacity(m, initialCapacity);
+
+        // Doubling from the expected size will cause exactly one
+        // resize, except near minimum capacity.
+        if (size > 1) {
+            growUsingPut(m, size);
+            assertCapacity(m, 2 * initialCapacity);
+        }
+
+        // Try again, growing with putAll()
+        m = new IdentityHashMap<>(size);
+        initialCapacity = capacity(m);
+        growUsingPutAll(m, size);
+        assertCapacity(m, initialCapacity);
+
+        // Doubling from the expected size will cause exactly one
+        // resize, except near minimum capacity.
+        if (size > 1) {
+            growUsingPutAll(m, size);
+            assertCapacity(m, 2 * initialCapacity);
+        }
+    }
+
+    /**
+     * Given the expected size, computes such a number N of items that
+     * inserting (N+1) items will trigger resizing of the internal storage
+     */
+    static int threshold(int size) throws Throwable {
+        IdentityHashMap<Object,Object> m = new IdentityHashMap<>(size);
+        int initialCapacity = capacity(m);
+        while (capacity(m) == initialCapacity)
+            growUsingPut(m, 1);
+        return m.size() - 1;
+    }
+
+    /**
+     * Checks that inserting (threshold+1) item causes resizing
+     * of the internal storage
+     */
+    @Test(dataProvider = "sizes")
+    public void passingThresholdCausesResize(int size) throws Throwable {
+        final int threshold = threshold(size);
+        IdentityHashMap<Object,Object> m = new IdentityHashMap<>(threshold);
+        int initialCapacity = capacity(m);
+
+        growUsingPut(m, threshold);
+        assertCapacity(m, initialCapacity);
+
+        growUsingPut(m, 1);
+        assertCapacity(m, 2 * initialCapacity);
+    }
+
+    /**
+     * Checks that 4 methods of requiring capacity lead to the same
+     * internal capacity, unless sized below default capacity.
+     */
+    @Test(dataProvider = "sizes")
+    public void differentGrowthPatternsResultInSameCapacity(int size)
+        throws Throwable {
+        if (size < 21)          // 21 is default maxExpectedSize
+            return;
+
+        IdentityHashMap<Object,Object> m;
+        m = new IdentityHashMap<Object,Object>(size);
+        int capacity1 = capacity(m);
+
+        m = new IdentityHashMap<>();
+        growUsingPut(m, size);
+        int capacity2 = capacity(m);
+
+        m = new IdentityHashMap<>();
+        growUsingPutAll(m, size);
+        int capacity3 = capacity(m);
+
+        m = new IdentityHashMap<>();
+        growUsingRepeatedPutAll(m, size);
+        int capacity4 = capacity(m);
+
+        if (capacity1 != capacity2 ||
+            capacity2 != capacity3 ||
+            capacity3 != capacity4)
+            throw new AssertionError("Capacities not equal: "
+                                     + capacity1 + " "
+                                     + capacity2 + " "
+                                     + capacity3 + " "
+                                     + capacity4);
+    }
+
+    public void defaultExpectedMaxSizeIs21() {
+        assertCapacity(new IdentityHashMap<Long,Long>(), 32);
+        assertCapacity(new IdentityHashMap<Long,Long>(21), 32);
+    }
+
+    public void minimumCapacityIs4() {
+        assertCapacity(new IdentityHashMap<Long,Long>(0), 4);
+        assertCapacity(new IdentityHashMap<Long,Long>(1), 4);
+        assertCapacity(new IdentityHashMap<Long,Long>(2), 4);
+        assertCapacity(new IdentityHashMap<Long,Long>(3), 8);
+    }
+
+    @Test(enabled = false)
+    /** needs too much memory to run normally */
+    public void maximumCapacityIs2ToThe29() {
+        assertCapacity(new IdentityHashMap<Long,Long>(Integer.MAX_VALUE),
+                       1 << 29);
+    }
+}