JDK-8210280 - Unnecessary reallocation when invoking HashMap.putAll()

[Chris Hegarty]

Martin,

Is it possible to use the the JDK’s test library jdk.test.lib.RandomFactory,
so that the initial seed is captured and repayable.

Also, please add the jtreg key so that the test is identifiable as using
randomness:  `@key randomness` .

-Chris.

> On 19 Dec 2018, at 14:47, Martin Buchholz <martinrb at google.com> wrote:
> 
> Let's add whitebox tests for initial capacity and LinkedHashMap, as with
> ConcurrentHashMap's whitebox tests.
> 
> --- src/test/jtreg/util/HashMap/WhiteBoxResizeTest.java 18 Dec 2018
> 20:21:24 -0000 1.1
> +++ src/test/jtreg/util/HashMap/WhiteBoxResizeTest.java 19 Dec 2018
> 14:35:50 -0000
> @@ -27,7 +27,11 @@
> 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;
> @@ -42,6 +46,7 @@
>  * @run testng WhiteBoxResizeTest
>  */
> public class WhiteBoxResizeTest {
> +    final ThreadLocalRandom rnd = ThreadLocalRandom.current();
>     final MethodHandle TABLE_SIZE_FOR;
>     final VarHandle THRESHOLD;
>     final VarHandle TABLE;
> @@ -91,14 +96,36 @@
>     }
> 
>     @Test
> -    public void capacityTest() {
> -        HashMap<Integer, Integer> map = new HashMap<>();
> +    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);
> +        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(1, 256);
> +        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));
> +        }
> +    }
> }