RFR: 8281631: HashMap copy constructor and putAll can over-allocate table [v24]

[XenoAmess]

On Thu, 3 Mar 2022 15:46:37 GMT, XenoAmess <duke at openjdk.java.net> wrote:

>> 8281631: HashMap copy constructor and putAll can over-allocate table
>
> XenoAmess has updated the pull request incrementally with one additional commit since the last revision:
> 
>   cast several float to double before calculation

I would ping the test codes here and you can run jtreg to see.

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import org.testng.annotations.Test;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.invoke.VarHandle;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.WeakHashMap;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.Supplier;
import java.util.stream.IntStream;

import static java.util.stream.Collectors.toMap;
import static org.testng.Assert.assertEquals;

/*
 * @test
 * @bug 8210280
 * @modules java.base/java.util:open
 * @summary White box tests for HashMap internals around table resize
 * @run testng WhiteBoxResizeTest
 * @key randomness
 */
public class WhiteBoxResizeTest {
    final ThreadLocalRandom rnd = ThreadLocalRandom.current();
    final MethodHandle TABLE_SIZE_FOR;
    final VarHandle THRESHOLD;
    final VarHandle TABLE;

    public WhiteBoxResizeTest() throws ReflectiveOperationException {
        Class<?> mClass = HashMap.class;
        String nodeClassName = mClass.getName() + "$Node";
        Class<?> nodeArrayClass = Class.forName("[L" + nodeClassName + ";");
        MethodHandles.Lookup lookup = MethodHandles.privateLookupIn(mClass, MethodHandles.lookup());
        TABLE = lookup.findVarHandle(mClass, "table", nodeArrayClass);
        this.TABLE_SIZE_FOR = lookup.findStatic(
                mClass, "tableSizeFor",
                MethodType.methodType(int.class, int.class));
        this.THRESHOLD = lookup.findVarHandle(mClass, "threshold", int.class);
    }

    int tableSizeFor(int n) {
        try {
            return (int) TABLE_SIZE_FOR.invoke(n);
        } catch (Throwable t) { throw new AssertionError(t); }
    }

    @Test
    public void testTableSizeFor() {
        assertEquals(tableSizeFor(0), 1);
        assertEquals(tableSizeFor(1), 1);
        assertEquals(tableSizeFor(2), 2);
        assertEquals(tableSizeFor(3), 4);
        assertEquals(tableSizeFor(15), 16);
        assertEquals(tableSizeFor(16), 16);
        assertEquals(tableSizeFor(17), 32);
        int maxSize = 1 << 30;
        assertEquals(tableSizeFor(maxSize - 1), maxSize);
        assertEquals(tableSizeFor(maxSize), maxSize);
        assertEquals(tableSizeFor(maxSize + 1), maxSize);
        assertEquals(tableSizeFor(Integer.MAX_VALUE), maxSize);
    }

    @Test
    public void capacityTestDefaultConstructor() throws NoSuchFieldException, IllegalAccessException {
        capacityTestDefaultConstructor(new HashMap<>());
        capacityTestDefaultConstructor(new LinkedHashMap<>());
        capacityTestDefaultConstructor(new WeakHashMap<>());
    }

    public static int getArrayLength(Map<?, ?> map) throws
            IllegalAccessException {
        Field field = null;
        Class<?> mapClass = map.getClass();
        while (!Map.class.equals(mapClass)) {
            try {
                field = mapClass.getDeclaredField("table");
                break;
            } catch (NoSuchFieldException ignored){
            }
            mapClass = mapClass.getSuperclass();
        }
        Objects.requireNonNull(field);
        field.setAccessible(true);
        Object table = field.get(map);
        if (table == null) {
            return -1;
        }
        return Array.getLength(table);
    }

    void capacityTestDefaultConstructor(
            Map<Integer, Integer> map
    ) throws IllegalAccessException {
        assertEquals(getArrayLength(map), -1);

        map.put(1, 1);
        assertEquals(getArrayLength(map), 16); // default initial capacity

        map.putAll(IntStream.range(0, 64).boxed().collect(toMap(i -> i, i -> i)));
        assertEquals(getArrayLength(map), 128);
    }

    @Test
    public void capacityTestInitialCapacity() throws NoSuchFieldException, IllegalAccessException {
        int initialCapacity = rnd.nextInt(2, 128);
        List<Supplier<Map<Integer, Integer>>> suppliers = List.of(
                () -> new HashMap<>(initialCapacity),
                () -> new HashMap<>(initialCapacity, 0.75f),
                () -> new LinkedHashMap<>(initialCapacity),
                () -> new LinkedHashMap<>(initialCapacity, 0.75f),
                () -> new WeakHashMap<>(initialCapacity),
                () -> new WeakHashMap<>(initialCapacity, 0.75f));

        for (Supplier<Map<Integer, Integer>> supplier : suppliers) {
            Map<Integer, Integer> map = supplier.get();
            assertEquals(-1, getArrayLength(map));

            map.put(1, 1);
            assertEquals(getArrayLength(map), tableSizeFor(initialCapacity));
        }
    }
}

I do think creating such mechanism for WeakHashMap is benifitial, and would like to do it in another pr, but that sounds not much related to this issue.
Let's do this first and then we do that next.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7431