/*
* 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
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*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Martin Buchholz with assistance from members of JCP
* JSR-166 Expert Group and released to the public domain, as
* explained at http://creativecommons.org/publicdomain/zero/1.0/
*/
/*
* @test
* @modules java.base/java.util.concurrent:open
* @run testng WhiteBox
* @summary White box tests of implementation details
*/
import static org.testng.Assert.*;
import org.testng.annotations.DataProvider;
import org.testng.annotations.Test;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ThreadLocalRandom;
import static java.util.stream.Collectors.toList;
import java.util.function.Consumer;
@Test
public class WhiteBox {
final ThreadLocalRandom rnd = ThreadLocalRandom.current();
final VarHandle HEAD, TAIL, ITEM, NEXT;
WhiteBox() throws ReflectiveOperationException {
Class<?> qClass = ConcurrentLinkedQueue.class;
Class<?> nodeClass = Class.forName(qClass.getName() + "$Node");
MethodHandles.Lookup lookup
= MethodHandles.privateLookupIn(qClass, MethodHandles.lookup());
HEAD = lookup.findVarHandle(qClass, "head", nodeClass);
TAIL = lookup.findVarHandle(qClass, "tail", nodeClass);
NEXT = lookup.findVarHandle(nodeClass, "next", nodeClass);
ITEM = lookup.findVarHandle(nodeClass, "item", Object.class);
}
Object head(ConcurrentLinkedQueue q) { return HEAD.getVolatile(q); }
Object tail(ConcurrentLinkedQueue q) { return TAIL.getVolatile(q); }
Object item(Object node) { return ITEM.getVolatile(node); }
Object next(Object node) { return NEXT.getVolatile(node); }
int nodeCount(ConcurrentLinkedQueue q) {
int i = 0;
for (Object p = head(q); p != null; ) {
i++;
if (p == (p = next(p))) p = head(q);
}
return i;
}
void assertIsSelfLinked(Object node) {
assertSame(next(node), node);
assertNull(item(node));
}
void assertIsNotSelfLinked(Object node) {
assertNotSame(node, next(node));
}
@Test
public void addRemove() {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
assertInvariants(q);
assertNull(item(head(q)));
assertEquals(nodeCount(q), 1);
q.add(1);
assertEquals(nodeCount(q), 2);
assertInvariants(q);
q.remove(1);
assertEquals(nodeCount(q), 1);
assertInvariants(q);
}
/**
* Traversal actions that visit every node and do nothing, but
* have side effect of squeezing out dead nodes.
*/
@DataProvider
public Object[][] traversalActions() {
return List.<Consumer<ConcurrentLinkedQueue>>of(
q -> q.forEach(e -> {}),
q -> assertFalse(q.contains(new Object())),
q -> assertFalse(q.remove(new Object())),
q -> q.spliterator().forEachRemaining(e -> {}),
q -> q.stream().collect(toList()),
q -> assertFalse(q.removeIf(e -> false)),
q -> assertFalse(q.removeAll(List.of())))
.stream().map(x -> new Object[]{ x }).toArray(Object[][]::new);
}
@Test(dataProvider = "traversalActions")
public void traversalOperationsCollapseNodes(
Consumer<ConcurrentLinkedQueue> traversalAction) {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
Object oldHead;
int n = 1 + rnd.nextInt(5);
for (int i = 0; i < n; i++) q.add(i);
assertInvariants(q);
assertEquals(nodeCount(q), n + 1);
oldHead = head(q);
traversalAction.accept(q); // collapses head node
assertIsSelfLinked(oldHead);
assertInvariants(q);
assertEquals(nodeCount(q), n);
// Iterator.remove does not currently try to collapse dead nodes
for (Iterator it = q.iterator(); it.hasNext(); ) {
it.next();
it.remove();
}
assertEquals(nodeCount(q), n);
assertInvariants(q);
oldHead = head(q);
traversalAction.accept(q); // collapses all nodes
if (n > 1) assertIsSelfLinked(oldHead);
assertEquals(nodeCount(q), 1);
assertInvariants(q);
for (int i = 0; i < n + 1; i++) q.add(i);
assertEquals(nodeCount(q), n + 2);
oldHead = head(q);
assertEquals(0, q.poll()); // 2 leading nodes collapsed
assertIsSelfLinked(oldHead);
assertEquals(nodeCount(q), n);
assertTrue(q.remove(n));
assertEquals(nodeCount(q), n);
traversalAction.accept(q); // trailing node is never collapsed
}
@Test(dataProvider = "traversalActions")
public void traversalOperationsCollapseLeadingNodes(
Consumer<ConcurrentLinkedQueue> traversalAction) {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
Object oldHead;
int n = 1 + rnd.nextInt(5);
for (int i = 0; i < n; i++) q.add(i);
assertEquals(nodeCount(q), n + 1);
oldHead = head(q);
traversalAction.accept(q);
assertInvariants(q);
assertEquals(nodeCount(q), n);
assertIsSelfLinked(oldHead);
}
@Test(dataProvider = "traversalActions")
public void traversalOperationsDoNotSelfLinkInteriorNodes(
Consumer<ConcurrentLinkedQueue> traversalAction) {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
int c;
int n = 3 + rnd.nextInt(3);
for (int i = 0; i < n; i++) q.add(i);
Object oneNode;
for (oneNode = head(q);
! (item(oneNode) != null && item(oneNode).equals(1));
oneNode = next(oneNode))
;
Object next = next(oneNode);
c = nodeCount(q);
for (Iterator it = q.iterator(); it.hasNext(); )
if (it.next().equals(1)) it.remove();
assertEquals(nodeCount(q), c - 1); // iterator detached head!
assertNull(item(oneNode));
assertSame(next, next(oneNode));
assertInvariants(q);
c = nodeCount(q);
traversalAction.accept(q);
assertEquals(nodeCount(q), c - 1);
assertSame(next, next(oneNode)); // un-linked, but not self-linked
}
/**
* Checks that traversal operations collapse a random pattern of
* dead nodes as could normally only occur with a race.
*/
@Test(dataProvider = "traversalActions")
public void traversalOperationsCollapseRandomNodes(
Consumer<ConcurrentLinkedQueue> traversalAction) {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
int n = rnd.nextInt(6);
for (int i = 0; i < n; i++) q.add(i);
ArrayList nulledOut = new ArrayList();
for (Object p = head(q); p != null; p = next(p))
if (item(p) != null && rnd.nextBoolean()) {
nulledOut.add(item(p));
ITEM.setVolatile(p, null);
}
traversalAction.accept(q);
int c = nodeCount(q);
assertEquals(q.size(), c - (q.contains(n - 1) ? 0 : 1));
for (int i = 0; i < n; i++)
assertTrue(nulledOut.contains(i) ^ q.contains(i));
}
/**
* Traversal actions that remove every element, and are also
* expected to squeeze out dead nodes.
*/
@DataProvider
public Object[][] bulkRemovalActions() {
return List.<Consumer<ConcurrentLinkedQueue>>of(
q -> q.clear(),
q -> assertTrue(q.removeIf(e -> true)),
q -> assertTrue(q.retainAll(List.of())))
.stream().map(x -> new Object[]{ x }).toArray(Object[][]::new);
}
@Test(dataProvider = "bulkRemovalActions")
public void bulkRemovalOperationsCollapseNodes(
Consumer<ConcurrentLinkedQueue> bulkRemovalAction) {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
int n = 1 + rnd.nextInt(5);
for (int i = 0; i < n; i++) q.add(i);
bulkRemovalAction.accept(q);
assertEquals(nodeCount(q), 1);
assertInvariants(q);
}
/**
* Actions that remove the first element, and are expected to
* leave at most one slack dead node at head.
*/
@DataProvider
public Object[][] pollActions() {
return List.<Consumer<ConcurrentLinkedQueue>>of(
q -> assertNotNull(q.poll()),
q -> assertNotNull(q.remove()))
.stream().map(x -> new Object[]{ x }).toArray(Object[][]::new);
}
@Test(dataProvider = "pollActions")
public void pollActionsOneNodeSlack(
Consumer<ConcurrentLinkedQueue> pollAction) {
ConcurrentLinkedQueue q = new ConcurrentLinkedQueue();
int n = 1 + rnd.nextInt(5);
for (int i = 0; i < n; i++) q.add(i);
assertEquals(nodeCount(q), n + 1);
for (int i = 0; i < n; i++) {
int c = nodeCount(q);
boolean slack = item(head(q)) == null;
if (slack) assertNotNull(item(next(head(q))));
pollAction.accept(q);
assertEquals(nodeCount(q), q.isEmpty() ? 1 : c - (slack ? 2 : 0));
}
assertInvariants(q);
}
byte[] serialBytes(Object o) {
try {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(o);
oos.flush();
oos.close();
return bos.toByteArray();
} catch (Exception fail) {
throw new AssertionError(fail);
}
}
@SuppressWarnings("unchecked")
<T> T serialClone(T o) {
try {
ObjectInputStream ois = new ObjectInputStream
(new ByteArrayInputStream(serialBytes(o)));
T clone = (T) ois.readObject();
assertNotSame(o, clone);
assertSame(o.getClass(), clone.getClass());
return clone;
} catch (Exception fail) {
throw new AssertionError(fail);
}
}
@Test
public void testSerialization() {
ConcurrentLinkedQueue q = serialClone(new ConcurrentLinkedQueue());
assertInvariants(q);
}
/** Checks conditions which should always be true. */
void assertInvariants(ConcurrentLinkedQueue q) {
assertNotNull(head(q));
assertNotNull(tail(q));
// head is never self-linked (but tail may!)
for (Object h; next(h = head(q)) == h; )
assertNotSame(h, head(q)); // must be update race
}
}