WhiteBoxResizeTest.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
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;
import static org.testng.Assert.assertNull;

/*
 * @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); }
    }

    Object[] table(HashMap map) {
        try {
            return (Object[]) TABLE.get(map);
        } catch (Throwable t) { throw new AssertionError(t); }
    }

    int capacity(HashMap map) {
        return table(map).length;
    }

    @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() {
        capacityTestDefaultConstructor(new HashMap<>());
        capacityTestDefaultConstructor(new LinkedHashMap<>());
    }

    void capacityTestDefaultConstructor(HashMap<Integer, Integer> map) {
        assertNull(table(map));

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

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

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

        for (Supplier<HashMap<Integer, Integer>> supplier : suppliers) {
            HashMap<Integer, Integer> map = supplier.get();
            assertNull(table(map));

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