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8156071: List.of: reduce array copying during creation

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Reviewed-by: psandoz, redestad
This commit is contained in:
Stuart Marks 2020-10-05 17:00:57 +00:00
parent ea27a54bf0
commit 88d75c9ad5
6 changed files with 203 additions and 18 deletions
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33
src/java.base/share/classes/java/util/ImmutableCollections.java
View file

@ -36,6 +36,7 @@ import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import jdk.internal.access.JavaUtilCollectionAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.CDS;
import jdk.internal.vm.annotation.Stable;
@ -103,7 +104,7 @@ class ImmutableCollections {
CDS.initializeFromArchive(ImmutableCollections.class);
if (archivedObjects == null) {
EMPTY = new Object();
EMPTY_LIST = new ListN<>();
EMPTY_LIST = new ListN<>(new Object[0]);
EMPTY_SET = new SetN<>();
EMPTY_MAP = new MapN<>();
archivedObjects = new Object[] { EMPTY, EMPTY_LIST, EMPTY_SET, EMPTY_MAP };
@ -115,6 +116,16 @@ class ImmutableCollections {
}
}
static class Access {
static {
SharedSecrets.setJavaUtilCollectionAccess(new JavaUtilCollectionAccess() {
public <E> List<E> listFromTrustedArray(Object[] array) {
return ImmutableCollections.ListN.fromTrustedArray(array);
}
});
}
}
/** No instances. */
private ImmutableCollections() { }
@ -521,15 +532,31 @@ class ImmutableCollections {
@Stable
private final E[] elements;
private ListN(E[] array) {
elements = array;
}
// creates a new internal array, and checks and rejects null elements
@SafeVarargs
ListN(E... input) {
static <E> List<E> fromArray(E... input) {
// copy and check manually to avoid TOCTOU
@SuppressWarnings("unchecked")
E[] tmp = (E[])new Object[input.length]; // implicit nullcheck of input
for (int i = 0; i < input.length; i++) {
tmp[i] = Objects.requireNonNull(input[i]);
}
elements = tmp;
return new ListN<>(tmp);
}
// Avoids creating a new array, but checks and rejects null elements.
// Declared with Object... arg so that varargs calls don't accidentally
// create an array of a subtype.
@SuppressWarnings("unchecked")
static <E> List<E> fromTrustedArray(Object... input) {
for (Object o : input) {
Objects.requireNonNull(o);
}
return new ListN<>((E[])input);
}
@Override

28
src/java.base/share/classes/java/util/List.java
View file

@ -842,7 +842,7 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3) {
return new ImmutableCollections.ListN<>(e1, e2, e3);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3);
}
/**
@ -861,7 +861,7 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4);
}
/**
@ -881,7 +881,7 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4, e5);
}
/**
@ -902,8 +902,8 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5,
e6);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4, e5,
e6);
}
/**
@ -925,8 +925,8 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5,
e6, e7);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4, e5,
e6, e7);
}
/**
@ -949,8 +949,8 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5,
e6, e7, e8);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4, e5,
e6, e7, e8);
}
/**
@ -974,8 +974,8 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5,
e6, e7, e8, e9);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4, e5,
e6, e7, e8, e9);
}
/**
@ -1000,8 +1000,8 @@ public interface List<E> extends Collection<E> {
* @since 9
*/
static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5,
e6, e7, e8, e9, e10);
return ImmutableCollections.ListN.fromTrustedArray(e1, e2, e3, e4, e5,
e6, e7, e8, e9, e10);
}
/**
@ -1042,7 +1042,7 @@ public interface List<E> extends Collection<E> {
case 2:
return new ImmutableCollections.List12<>(elements[0], elements[1]);
default:
return new ImmutableCollections.ListN<>(elements);
return ImmutableCollections.ListN.fromArray(elements);
}
}

5
src/java.base/share/classes/java/util/stream/Collectors.java
View file

@ -56,6 +56,8 @@ import java.util.function.ToDoubleFunction;
import java.util.function.ToIntFunction;
import java.util.function.ToLongFunction;
import jdk.internal.access.SharedSecrets;
/**
* Implementations of {@link Collector} that implement various useful reduction
* operations, such as accumulating elements into collections, summarizing
@ -296,7 +298,8 @@ public final class Collectors {
Collector<T, ?, List<T>> toUnmodifiableList() {
return new CollectorImpl<>((Supplier<List<T>>) ArrayList::new, List::add,
(left, right) -> { left.addAll(right); return left; },
list -> (List<T>)List.of(list.toArray()),
list -> (List<T>)SharedSecrets.getJavaUtilCollectionAccess()
.listFromTrustedArray(list.toArray()),
CH_NOID);
}