8149330: Capacity of StringBuilder should not get close to Integer.MAX_VALUE unless necessary

Reviewed-by: martin

src/share/classes/java/lang/AbstractStringBuilder.java

 /*
- * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2016, 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
@@ -112,29 +112,56 @@ abstract class AbstractStringBuilder implements Appendable, CharSequence {
     }
 
     /**
-     * This method has the same contract as ensureCapacity, but is
-     * never synchronized.
+     * For positive values of {@code minimumCapacity}, this method
+     * behaves like {@code ensureCapacity}, however it is never
+     * synchronized.
+     * If {@code minimumCapacity} is non positive due to numeric
+     * overflow, this method throws {@code OutOfMemoryError}.
      */
     private void ensureCapacityInternal(int minimumCapacity) {
         // overflow-conscious code
-        if (minimumCapacity - value.length > 0)
-            expandCapacity(minimumCapacity);
+        if (minimumCapacity - value.length > 0) {
+            value = Arrays.copyOf(value,
+                    newCapacity(minimumCapacity));
+        }
     }
 
     /**
-     * This implements the expansion semantics of ensureCapacity with no
-     * size check or synchronization.
+     * The maximum size of array to allocate (unless necessary).
+     * Some VMs reserve some header words in an array.
+     * Attempts to allocate larger arrays may result in
+     * OutOfMemoryError: Requested array size exceeds VM limit
+     */
+    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
+
+    /**
+     * Returns a capacity at least as large as the given minimum capacity.
+     * Returns the current capacity increased by the same amount + 2 if
+     * that suffices.
+     * Will not return a capacity greater than {@code MAX_ARRAY_SIZE}
+     * unless the given minimum capacity is greater than that.
+     *
+     * @param  minCapacity the desired minimum capacity
+     * @throws OutOfMemoryError if minCapacity is less than zero or
+     *         greater than Integer.MAX_VALUE
      */
-    void expandCapacity(int minimumCapacity) {
-        int newCapacity = value.length * 2 + 2;
-        if (newCapacity - minimumCapacity < 0)
-            newCapacity = minimumCapacity;
-        if (newCapacity < 0) {
-            if (minimumCapacity < 0) // overflow
-                throw new OutOfMemoryError();
-            newCapacity = Integer.MAX_VALUE;
+    private int newCapacity(int minCapacity) {
+        // overflow-conscious code
+        int newCapacity = (value.length << 1) + 2;
+        if (newCapacity - minCapacity < 0) {
+            newCapacity = minCapacity;
+        }
+        return (newCapacity <= 0 || MAX_ARRAY_SIZE - newCapacity < 0)
+            ? hugeCapacity(minCapacity)
+            : newCapacity;
+    }
+
+    private int hugeCapacity(int minCapacity) {
+        if (Integer.MAX_VALUE - minCapacity < 0) { // overflow
+            throw new OutOfMemoryError();
         }
-        value = Arrays.copyOf(value, newCapacity);
+        return (minCapacity > MAX_ARRAY_SIZE)
+            ? minCapacity : MAX_ARRAY_SIZE;
     }
 
     /**

src/share/classes/java/lang/StringBuffer.java

@@ -171,9 +171,7 @@ import java.util.Arrays;
 
     @Override
     public synchronized void ensureCapacity(int minimumCapacity) {
-        if (minimumCapacity > value.length) {
-            expandCapacity(minimumCapacity);
-        }
+        super.ensureCapacity(minimumCapacity);
     }
 
     /**

test/java/lang/StringBuilder/Capacity.java

+/*
+ * Copyright (c) 2016, 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.
+ */
+
+/*
+ * @test
+ * @bug 8149330
+ * @summary Basic set of tests of capacity management
+ * @run testng Capacity
+ */
+
+import java.lang.reflect.Field;
+import java.util.AbstractList;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.SplittableRandom;
+
+import org.testng.annotations.Test;
+import org.testng.annotations.DataProvider;
+import static org.testng.Assert.*;
+
+public class Capacity {
+    static final int DEFAULT_CAPACITY = 16;
+
+    private static int newCapacity(int oldCapacity,
+            int desiredCapacity)
+    {
+        return Math.max(oldCapacity * 2 + 2, desiredCapacity);
+    }
+
+    private static int nextNewCapacity(int oldCapacity) {
+        return newCapacity(oldCapacity, oldCapacity + 1);
+    }
+
+    @Test(dataProvider = "singleChar")
+    public void defaultCapacity(Character ch) {
+        StringBuilder sb = new StringBuilder();
+        assertEquals(sb.capacity(), DEFAULT_CAPACITY);
+        for (int i = 0; i < DEFAULT_CAPACITY; i++) {
+            sb.append(ch);
+            assertEquals(sb.capacity(), DEFAULT_CAPACITY);
+        }
+        sb.append(ch);
+        assertEquals(sb.capacity(), nextNewCapacity(DEFAULT_CAPACITY));
+    }
+
+    @Test(dataProvider = "charCapacity")
+    public void explicitCapacity(Character ch, int initCapacity) {
+        StringBuilder sb = new StringBuilder(initCapacity);
+        assertEquals(sb.capacity(), initCapacity);
+        for (int i = 0; i < initCapacity; i++) {
+            sb.append(ch);
+            assertEquals(sb.capacity(), initCapacity);
+        }
+        sb.append(ch);
+        assertEquals(sb.capacity(), nextNewCapacity(initCapacity));
+    }
+
+    @Test(dataProvider = "singleChar")
+    public void sbFromString(Character ch) {
+        String s = "string " + ch;
+        int expectedCapacity = s.length() + DEFAULT_CAPACITY;
+        StringBuilder sb = new StringBuilder(s);
+        assertEquals(sb.capacity(), expectedCapacity);
+        for (int i = 0; i < DEFAULT_CAPACITY; i++) {
+            sb.append(ch);
+            assertEquals(sb.capacity(), expectedCapacity);
+        }
+        sb.append(ch);
+        assertEquals(sb.capacity(), nextNewCapacity(expectedCapacity));
+    }
+
+    @Test(dataProvider = "singleChar")
+    public void sbFromCharSeq(Character ch) {
+        CharSequence cs = new MyCharSeq("char seq " + ch);
+        int expectedCapacity = cs.length() + DEFAULT_CAPACITY;
+        StringBuilder sb = new StringBuilder(cs);
+        assertEquals(sb.capacity(), expectedCapacity);
+        for (int i = 0; i < DEFAULT_CAPACITY; i++) {
+            sb.append(ch);
+            assertEquals(sb.capacity(), expectedCapacity);
+        }
+        sb.append(ch);
+        assertEquals(sb.capacity(), nextNewCapacity(expectedCapacity));
+    }
+
+    @Test(dataProvider = "charCapacity")
+    public void ensureCapacity(Character ch, int cap) {
+        StringBuilder sb = new StringBuilder(0);
+        assertEquals(sb.capacity(), 0);
+        sb.ensureCapacity(cap); // only has effect if cap > 0
+        int newCap = (cap == 0) ? 0 : newCapacity(0, cap);
+        assertEquals(sb.capacity(), newCap);
+        sb.ensureCapacity(newCap + 1);
+        assertEquals(sb.capacity(), nextNewCapacity(newCap));
+        sb.append(ch);
+        assertEquals(sb.capacity(), nextNewCapacity(newCap));
+    }
+
+    @Test(dataProvider = "negativeCapacity",
+          expectedExceptions = NegativeArraySizeException.class)
+    public void negativeInitialCapacity(int negCap) {
+        StringBuilder sb = new StringBuilder(negCap);
+    }
+
+    @Test(dataProvider = "negativeCapacity")
+    public void ensureNegativeCapacity(int negCap) {
+        StringBuilder sb = new StringBuilder();
+        sb.ensureCapacity(negCap);
+        assertEquals(sb.capacity(), DEFAULT_CAPACITY);
+    }
+
+    @Test(dataProvider = "charCapacity")
+    public void trimToSize(Character ch, int cap) {
+        StringBuilder sb = new StringBuilder(cap);
+        int halfOfCap = cap / 2;
+        for (int i = 0; i < halfOfCap; i++) {
+            sb.append(ch);
+        }
+        sb.trimToSize();
+        // according to the spec, capacity doesn't have to
+        // become exactly the size
+        assertTrue(sb.capacity() >= halfOfCap);
+    }
+
+    @DataProvider
+    public Object[][] singleChar() {
+        return new Object[][] { {'J'}, {'\u042b'} };
+    }
+
+    @DataProvider
+    public Object[][] charCapacity() {
+        return new Object[][] {
+            {'J', 0},
+            {'J', 1},
+            {'J', 15},
+            {'J', DEFAULT_CAPACITY},
+            {'J', 1024},
+            {'\u042b', 0},
+            {'\u042b', 1},
+            {'\u042b', 15},
+            {'\u042b', DEFAULT_CAPACITY},
+            {'\u042b', 1024},
+        };
+    }
+
+    @DataProvider
+    public Object[][] negativeCapacity() {
+        return new Object[][] { {-1}, {Integer.MIN_VALUE} };
+    }
+
+    private static class MyCharSeq implements CharSequence {
+        private CharSequence s;
+        public MyCharSeq(CharSequence s) { this.s = s; }
+        public char charAt(int i) { return s.charAt(i); }
+        public int length() { return s.length(); }
+        public CharSequence subSequence(int st, int e) {
+            return s.subSequence(st, e);
+        }
+        public String toString() { return s.toString(); }
+    }
+}

test/java/lang/StringBuilder/HugeCapacity.java

+/*
+ * Copyright (c) 2016, 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.
+ */
+
+/**
+ * @test
+ * @bug 8149330
+ * @summary Capacity should not get close to Integer.MAX_VALUE unless
+ *          necessary
+ * @run main/othervm -Xmx10G HugeCapacity
+ * @ignore This test has huge memory requirements
+ */
+
+public class HugeCapacity {
+    private static int failures = 0;
+
+    public static void main(String[] args) {
+        testLatin1();
+        testUtf16();
+        if (failures > 0) {
+            throw new RuntimeException(failures + " tests failed");
+        }
+    }
+
+    private static void testLatin1() {
+        try {
+            StringBuilder sb = new StringBuilder();
+            sb.ensureCapacity(Integer.MAX_VALUE / 2);
+            sb.ensureCapacity(Integer.MAX_VALUE / 2 + 1);
+        } catch (OutOfMemoryError oom) {
+            oom.printStackTrace();
+            failures++;
+        }
+    }
+
+    private static void testUtf16() {
+        try {
+            StringBuilder sb = new StringBuilder();
+            sb.append('\u042b');
+            sb.ensureCapacity(Integer.MAX_VALUE / 4);
+            sb.ensureCapacity(Integer.MAX_VALUE / 4 + 1);
+        } catch (OutOfMemoryError oom) {
+            oom.printStackTrace();
+            failures++;
+        }
+    }
+}