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Comparing jsr166/src/test/tck/ConcurrentLinkedDequeTest.java (file contents):
Revision 1.3 by jsr166, Wed Nov 3 16:46:34 2010 UTC vs.
Revision 1.31 by jsr166, Sun Oct 22 21:52:58 2017 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		* Other contributors include Andrew Wright, Jeffrey Hayes,
6		* Pat Fisher, Mike Judd.
7		*/
8
9	<	import junit.framework.*;
10	<	import java.util.*;
11	<	import java.util.concurrent.*;
12	<	import java.io.*;
9	>	import java.util.Arrays;
10	>	import java.util.Collection;
11	>	import java.util.Deque;
12	>	import java.util.Iterator;
13	>	import java.util.NoSuchElementException;
14	>	import java.util.Queue;
15	>	import java.util.Random;
16	>	import java.util.concurrent.CompletableFuture;
17	>	import java.util.concurrent.ConcurrentLinkedDeque;
18	>	import java.util.concurrent.ThreadLocalRandom;
19	>	import java.util.concurrent.atomic.LongAdder;
20	>
21	>	import junit.framework.Test;
22
23		public class ConcurrentLinkedDequeTest extends JSR166TestCase {
24
25		public static void main(String[] args) {
26	<	junit.textui.TestRunner.run(suite());
26	>	main(suite(), args);
27		}
28
29		public static Test suite() {
30	<	return new TestSuite(ConcurrentLinkedDequeTest.class);
30	>	class Implementation implements CollectionImplementation {
31	>	public Class<?> klazz() { return ConcurrentLinkedDeque.class; }
32	>	public Collection emptyCollection() { return new ConcurrentLinkedDeque(); }
33	>	public Object makeElement(int i) { return i; }
34	>	public boolean isConcurrent() { return true; }
35	>	public boolean permitsNulls() { return false; }
36	>	}
37	>	return newTestSuite(ConcurrentLinkedDequeTest.class,
38	>	CollectionTest.testSuite(new Implementation()));
39		}
40
41		/**
42	<	* Create a deque of given size containing consecutive
43	<	* Integers 0 ... n.
42	>	* Returns a new deque of given size containing consecutive
43	>	* Integers 0 ... n - 1.
44		*/
45	<	private ConcurrentLinkedDeque populatedDeque(int n) {
46	<	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
45	>	private static ConcurrentLinkedDeque<Integer> populatedDeque(int n) {
46	>	ConcurrentLinkedDeque<Integer> q = new ConcurrentLinkedDeque<>();
47		assertTrue(q.isEmpty());
48		for (int i = 0; i < n; ++i)
49		assertTrue(q.offer(new Integer(i)));
50		assertFalse(q.isEmpty());
51		assertEquals(n, q.size());
52	+	assertEquals((Integer) 0, q.peekFirst());
53	+	assertEquals((Integer) (n - 1), q.peekLast());
54		return q;
55		}
56
#	Line 48 | Line 67 | public class ConcurrentLinkedDequeTest e
67		*/
68		public void testConstructor3() {
69		try {
70	<	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque((Collection)null);
70	>	new ConcurrentLinkedDeque((Collection)null);
71		shouldThrow();
72		} catch (NullPointerException success) {}
73		}
#	Line 58 | Line 77 | public class ConcurrentLinkedDequeTest e
77		*/
78		public void testConstructor4() {
79		try {
80	<	Integer[] ints = new Integer[SIZE];
62	<	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque(Arrays.asList(ints));
80	>	new ConcurrentLinkedDeque(Arrays.asList(new Integer[SIZE]));
81		shouldThrow();
82		} catch (NullPointerException success) {}
83		}
#	Line 68 | Line 86 | public class ConcurrentLinkedDequeTest e
86		* Initializing from Collection with some null elements throws NPE
87		*/
88		public void testConstructor5() {
89	+	Integer[] ints = new Integer[SIZE];
90	+	for (int i = 0; i < SIZE - 1; ++i)
91	+	ints[i] = new Integer(i);
92		try {
93	<	Integer[] ints = new Integer[SIZE];
73	<	for (int i = 0; i < SIZE-1; ++i)
74	<	ints[i] = new Integer(i);
75	<	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque(Arrays.asList(ints));
93	>	new ConcurrentLinkedDeque(Arrays.asList(ints));
94		shouldThrow();
95		} catch (NullPointerException success) {}
96		}
#	Line 109 | Line 127 | public class ConcurrentLinkedDequeTest e
127		public void testSize() {
128		ConcurrentLinkedDeque q = populatedDeque(SIZE);
129		for (int i = 0; i < SIZE; ++i) {
130	<	assertEquals(SIZE-i, q.size());
130	>	assertEquals(SIZE - i, q.size());
131		q.remove();
132		}
133		for (int i = 0; i < SIZE; ++i) {
#	Line 122 | Line 140 | public class ConcurrentLinkedDequeTest e
140		* push(null) throws NPE
141		*/
142		public void testPushNull() {
143	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
144		try {
126	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
145		q.push(null);
146		shouldThrow();
147		} catch (NullPointerException success) {}
#	Line 157 | Line 175 | public class ConcurrentLinkedDequeTest e
175		* offer(null) throws NPE
176		*/
177		public void testOfferNull() {
178	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
179		try {
161	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
180		q.offer(null);
181		shouldThrow();
182		} catch (NullPointerException success) {}
#	Line 168 | Line 186 | public class ConcurrentLinkedDequeTest e
186		* offerFirst(null) throws NPE
187		*/
188		public void testOfferFirstNull() {
189	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
190		try {
172	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
191		q.offerFirst(null);
192		shouldThrow();
193		} catch (NullPointerException success) {}
#	Line 179 | Line 197 | public class ConcurrentLinkedDequeTest e
197		* offerLast(null) throws NPE
198		*/
199		public void testOfferLastNull() {
200	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
201		try {
183	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
202		q.offerLast(null);
203		shouldThrow();
204		} catch (NullPointerException success) {}
#	Line 223 | Line 241 | public class ConcurrentLinkedDequeTest e
241		* add(null) throws NPE
242		*/
243		public void testAddNull() {
244	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
245		try {
227	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
246		q.add(null);
247		shouldThrow();
248		} catch (NullPointerException success) {}
#	Line 234 | Line 252 | public class ConcurrentLinkedDequeTest e
252		* addFirst(null) throws NPE
253		*/
254		public void testAddFirstNull() {
255	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
256		try {
238	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
257		q.addFirst(null);
258		shouldThrow();
259		} catch (NullPointerException success) {}
#	Line 245 | Line 263 | public class ConcurrentLinkedDequeTest e
263		* addLast(null) throws NPE
264		*/
265		public void testAddLastNull() {
266	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
267		try {
249	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
268		q.addLast(null);
269		shouldThrow();
270		} catch (NullPointerException success) {}
#	Line 289 | Line 307 | public class ConcurrentLinkedDequeTest e
307		* addAll(null) throws NPE
308		*/
309		public void testAddAll1() {
310	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
311		try {
293	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
312		q.addAll(null);
313		shouldThrow();
314		} catch (NullPointerException success) {}
315		}
316
317		/**
318	<	* addAll(this) throws IAE
318	>	* addAll(this) throws IllegalArgumentException
319		*/
320		public void testAddAllSelf() {
321	+	ConcurrentLinkedDeque q = populatedDeque(SIZE);
322		try {
304	–	ConcurrentLinkedDeque q = populatedDeque(SIZE);
323		q.addAll(q);
324		shouldThrow();
325		} catch (IllegalArgumentException success) {}
#	Line 311 | Line 329 | public class ConcurrentLinkedDequeTest e
329		* addAll of a collection with null elements throws NPE
330		*/
331		public void testAddAll2() {
332	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
333		try {
334	<	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
316	<	Integer[] ints = new Integer[SIZE];
317	<	q.addAll(Arrays.asList(ints));
334	>	q.addAll(Arrays.asList(new Integer[SIZE]));
335		shouldThrow();
336		} catch (NullPointerException success) {}
337		}
#	Line 324 | Line 341 | public class ConcurrentLinkedDequeTest e
341		* possibly adding some elements
342		*/
343		public void testAddAll3() {
344	+	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
345	+	Integer[] ints = new Integer[SIZE];
346	+	for (int i = 0; i < SIZE - 1; ++i)
347	+	ints[i] = new Integer(i);
348		try {
328	–	ConcurrentLinkedDeque q = new ConcurrentLinkedDeque();
329	–	Integer[] ints = new Integer[SIZE];
330	–	for (int i = 0; i < SIZE-1; ++i)
331	–	ints[i] = new Integer(i);
349		q.addAll(Arrays.asList(ints));
350		shouldThrow();
351		} catch (NullPointerException success) {}
#	Line 365 | Line 382 | public class ConcurrentLinkedDequeTest e
382		*/
383		public void testPollLast() {
384		ConcurrentLinkedDeque q = populatedDeque(SIZE);
385	<	for (int i = SIZE-1; i >= 0; --i) {
385	>	for (int i = SIZE - 1; i >= 0; --i) {
386		assertEquals(i, q.pollLast());
387		}
388		assertNull(q.pollLast());
#	Line 430 | Line 447 | public class ConcurrentLinkedDequeTest e
447		*/
448		public void testRemoveElement() {
449		ConcurrentLinkedDeque q = populatedDeque(SIZE);
450	<	for (int i = 1; i < SIZE; i+=2) {
451	<	assertTrue(q.remove(new Integer(i)));
452	<	}
453	<	for (int i = 0; i < SIZE; i+=2) {
454	<	assertTrue(q.remove(new Integer(i)));
455	<	assertFalse(q.remove(new Integer(i+1)));
450	>	for (int i = 1; i < SIZE; i += 2) {
451	>	assertTrue(q.contains(i));
452	>	assertTrue(q.remove(i));
453	>	assertFalse(q.contains(i));
454	>	assertTrue(q.contains(i - 1));
455	>	}
456	>	for (int i = 0; i < SIZE; i += 2) {
457	>	assertTrue(q.contains(i));
458	>	assertTrue(q.remove(i));
459	>	assertFalse(q.contains(i));
460	>	assertFalse(q.remove(i + 1));
461	>	assertFalse(q.contains(i + 1));
462		}
463		assertTrue(q.isEmpty());
464		}
#	Line 459 | Line 482 | public class ConcurrentLinkedDequeTest e
482		*/
483		public void testPeekLast() {
484		ConcurrentLinkedDeque q = populatedDeque(SIZE);
485	<	for (int i = SIZE-1; i >= 0; --i) {
485	>	for (int i = SIZE - 1; i >= 0; --i) {
486		assertEquals(i, q.peekLast());
487		assertEquals(i, q.pollLast());
488		assertTrue(q.peekLast() == null ||
#	Line 488 | Line 511 | public class ConcurrentLinkedDequeTest e
511		*/
512		public void testLastElement() {
513		ConcurrentLinkedDeque q = populatedDeque(SIZE);
514	<	for (int i = SIZE-1; i >= 0; --i) {
514	>	for (int i = SIZE - 1; i >= 0; --i) {
515		assertEquals(i, q.getLast());
516		assertEquals(i, q.pollLast());
517		}
#	Line 534 | Line 557 | public class ConcurrentLinkedDequeTest e
557		*/
558		public void testRemoveFirstOccurrence() {
559		ConcurrentLinkedDeque q = populatedDeque(SIZE);
560	<	for (int i = 1; i < SIZE; i+=2) {
560	>	for (int i = 1; i < SIZE; i += 2) {
561		assertTrue(q.removeFirstOccurrence(new Integer(i)));
562		}
563	<	for (int i = 0; i < SIZE; i+=2) {
563	>	for (int i = 0; i < SIZE; i += 2) {
564		assertTrue(q.removeFirstOccurrence(new Integer(i)));
565	<	assertFalse(q.removeFirstOccurrence(new Integer(i+1)));
565	>	assertFalse(q.removeFirstOccurrence(new Integer(i + 1)));
566		}
567		assertTrue(q.isEmpty());
568		}
#	Line 549 | Line 572 | public class ConcurrentLinkedDequeTest e
572		*/
573		public void testRemoveLastOccurrence() {
574		ConcurrentLinkedDeque q = populatedDeque(SIZE);
575	<	for (int i = 1; i < SIZE; i+=2) {
575	>	for (int i = 1; i < SIZE; i += 2) {
576		assertTrue(q.removeLastOccurrence(new Integer(i)));
577		}
578	<	for (int i = 0; i < SIZE; i+=2) {
578	>	for (int i = 0; i < SIZE; i += 2) {
579		assertTrue(q.removeLastOccurrence(new Integer(i)));
580	<	assertFalse(q.removeLastOccurrence(new Integer(i+1)));
580	>	assertFalse(q.removeLastOccurrence(new Integer(i + 1)));
581		}
582		assertTrue(q.isEmpty());
583		}
#	Line 613 | Line 636 | public class ConcurrentLinkedDequeTest e
636		assertTrue(changed);
637
638		assertTrue(q.containsAll(p));
639	<	assertEquals(SIZE-i, q.size());
639	>	assertEquals(SIZE - i, q.size());
640		p.remove();
641		}
642		}
#	Line 626 | Line 649 | public class ConcurrentLinkedDequeTest e
649		ConcurrentLinkedDeque q = populatedDeque(SIZE);
650		ConcurrentLinkedDeque p = populatedDeque(i);
651		assertTrue(q.removeAll(p));
652	<	assertEquals(SIZE-i, q.size());
652	>	assertEquals(SIZE - i, q.size());
653		for (int j = 0; j < i; ++j) {
654	<	Integer I = (Integer)(p.remove());
655	<	assertFalse(q.contains(I));
654	>	Integer x = (Integer)(p.remove());
655	>	assertFalse(q.contains(x));
656		}
657		}
658		}
659
660		/**
661	<	* toArray() contains all elements
661	>	* toArray() contains all elements in FIFO order
662		*/
663		public void testToArray() {
664		ConcurrentLinkedDeque q = populatedDeque(SIZE);
665		Object[] o = q.toArray();
643	–	Arrays.sort(o);
666		for (int i = 0; i < o.length; i++)
667	<	assertEquals(o[i], q.poll());
667	>	assertSame(o[i], q.poll());
668		}
669
670		/**
671	<	* toArray(a) contains all elements
671	>	* toArray(a) contains all elements in FIFO order
672		*/
673		public void testToArray2() {
674	<	ConcurrentLinkedDeque q = populatedDeque(SIZE);
674	>	ConcurrentLinkedDeque<Integer> q = populatedDeque(SIZE);
675		Integer[] ints = new Integer[SIZE];
676	<	ints = (Integer[])q.toArray(ints);
677	<	Arrays.sort(ints);
676	>	Integer[] array = q.toArray(ints);
677	>	assertSame(ints, array);
678		for (int i = 0; i < ints.length; i++)
679	<	assertEquals(ints[i], q.poll());
679	>	assertSame(ints[i], q.poll());
680		}
681
682		/**
#	Line 684 | Line 706 | public class ConcurrentLinkedDequeTest e
706		*/
707		public void testIterator() {
708		ConcurrentLinkedDeque q = populatedDeque(SIZE);
687	–	int i = 0;
709		Iterator it = q.iterator();
710	<	while (it.hasNext()) {
710	>	int i;
711	>	for (i = 0; it.hasNext(); i++)
712		assertTrue(q.contains(it.next()));
691	–	++i;
692	–	}
713		assertEquals(i, SIZE);
714	+	assertIteratorExhausted(it);
715	+	}
716	+
717	+	/**
718	+	* iterator of empty collection has no elements
719	+	*/
720	+	public void testEmptyIterator() {
721	+	Deque c = new ConcurrentLinkedDeque();
722	+	assertIteratorExhausted(c.iterator());
723	+	assertIteratorExhausted(c.descendingIterator());
724		}
725
726		/**
#	Line 735 | Line 765 | public class ConcurrentLinkedDequeTest e
765		final Random rng = new Random();
766		for (int iters = 0; iters < 100; ++iters) {
767		int max = rng.nextInt(5) + 2;
768	<	int split = rng.nextInt(max-1) + 1;
768	>	int split = rng.nextInt(max - 1) + 1;
769		for (int j = 1; j <= max; ++j)
770		q.add(new Integer(j));
771		Iterator it = q.iterator();
772		for (int j = 1; j <= split; ++j)
773		assertEquals(it.next(), new Integer(j));
774		it.remove();
775	<	assertEquals(it.next(), new Integer(split+1));
775	>	assertEquals(it.next(), new Integer(split + 1));
776		for (int j = 1; j <= split; ++j)
777		q.remove(new Integer(j));
778		it = q.iterator();
779	<	for (int j = split+1; j <= max; ++j) {
779	>	for (int j = split + 1; j <= max; ++j) {
780		assertEquals(it.next(), new Integer(j));
781		it.remove();
782		}
#	Line 803 | Line 833 | public class ConcurrentLinkedDequeTest e
833		final Random rng = new Random();
834		for (int iters = 0; iters < 100; ++iters) {
835		int max = rng.nextInt(5) + 2;
836	<	int split = rng.nextInt(max-1) + 1;
836	>	int split = rng.nextInt(max - 1) + 1;
837		for (int j = max; j >= 1; --j)
838		q.add(new Integer(j));
839		Iterator it = q.descendingIterator();
840		for (int j = 1; j <= split; ++j)
841		assertEquals(it.next(), new Integer(j));
842		it.remove();
843	<	assertEquals(it.next(), new Integer(split+1));
843	>	assertEquals(it.next(), new Integer(split + 1));
844		for (int j = 1; j <= split; ++j)
845		q.remove(new Integer(j));
846		it = q.descendingIterator();
847	<	for (int j = split+1; j <= max; ++j) {
847	>	for (int j = split + 1; j <= max; ++j) {
848		assertEquals(it.next(), new Integer(j));
849		it.remove();
850		}
#	Line 830 | Line 860 | public class ConcurrentLinkedDequeTest e
860		ConcurrentLinkedDeque q = populatedDeque(SIZE);
861		String s = q.toString();
862		for (int i = 0; i < SIZE; ++i) {
863	<	assertTrue(s.indexOf(String.valueOf(i)) >= 0);
863	>	assertTrue(s.contains(String.valueOf(i)));
864		}
865		}
866
867		/**
868	<	* A deserialized serialized deque has same elements in same order
868	>	* A deserialized/reserialized deque has same elements in same order
869		*/
870		public void testSerialization() throws Exception {
871	<	ConcurrentLinkedDeque q = populatedDeque(SIZE);
872	<	ByteArrayOutputStream bout = new ByteArrayOutputStream(10000);
873	<	ObjectOutputStream out = new ObjectOutputStream(new BufferedOutputStream(bout));
874	<	out.writeObject(q);
875	<	out.close();
876	<
877	<	ByteArrayInputStream bin = new ByteArrayInputStream(bout.toByteArray());
878	<	ObjectInputStream in = new ObjectInputStream(new BufferedInputStream(bin));
879	<	ConcurrentLinkedDeque r = (ConcurrentLinkedDeque)in.readObject();
880	<	assertEquals(q.size(), r.size());
881	<	while (!q.isEmpty())
882	<	assertEquals(q.remove(), r.remove());
883	<	}
871	>	Queue x = populatedDeque(SIZE);
872	>	Queue y = serialClone(x);
873	>
874	>	assertNotSame(x, y);
875	>	assertEquals(x.size(), y.size());
876	>	assertEquals(x.toString(), y.toString());
877	>	assertTrue(Arrays.equals(x.toArray(), y.toArray()));
878	>	while (!x.isEmpty()) {
879	>	assertFalse(y.isEmpty());
880	>	assertEquals(x.remove(), y.remove());
881	>	}
882	>	assertTrue(y.isEmpty());
883	>	}
884	>
885	>	/**
886	>	* contains(null) always return false.
887	>	* remove(null) always throws NullPointerException.
888	>	*/
889	>	public void testNeverContainsNull() {
890	>	Deque<?>[] qs = {
891	>	new ConcurrentLinkedDeque<Object>(),
892	>	populatedDeque(2),
893	>	};
894	>
895	>	for (Deque<?> q : qs) {
896	>	assertFalse(q.contains(null));
897	>	try {
898	>	assertFalse(q.remove(null));
899	>	shouldThrow();
900	>	} catch (NullPointerException success) {}
901	>	try {
902	>	assertFalse(q.removeFirstOccurrence(null));
903	>	shouldThrow();
904	>	} catch (NullPointerException success) {}
905	>	try {
906	>	assertFalse(q.removeLastOccurrence(null));
907	>	shouldThrow();
908	>	} catch (NullPointerException success) {}
909	>	}
910	>	}
911	>
912	>	void runAsync(Runnable r1, Runnable r2) {
913	>	boolean b = ThreadLocalRandom.current().nextBoolean();
914	>	CompletableFuture<Void> f1 = CompletableFuture.runAsync(b ? r1 : r2);
915	>	CompletableFuture<Void> f2 = CompletableFuture.runAsync(b ? r2 : r1);
916	>	f1.join();
917	>	f2.join();
918	>	}
919	>
920	>	/**
921	>	* Non-traversing Deque operations are linearizable.
922	>	* https://bugs.openjdk.java.net/browse/JDK-8188900
923	>	* ant -Djsr166.expensiveTests=true -Djsr166.tckTestClass=ConcurrentLinkedDequeTest -Djsr166.methodFilter=testBug8188900 tck
924	>	*/
925	>	public void testBug8188900() {
926	>	final ThreadLocalRandom rnd = ThreadLocalRandom.current();
927	>	final LongAdder nulls = new LongAdder(), zeros = new LongAdder();
928	>	for (int n = expensiveTests ? 100_000 : 10; n--> 0; ) {
929	>	ConcurrentLinkedDeque<Integer> d = new ConcurrentLinkedDeque<>();
930	>
931	>	boolean peek = rnd.nextBoolean();
932	>	Runnable getter = () -> {
933	>	Integer x = peek ? d.peekFirst() : d.pollFirst();
934	>	if (x == null) nulls.increment();
935	>	else if (x == 0) zeros.increment();
936	>	else
937	>	throw new AssertionError(
938	>	String.format(
939	>	"unexpected value %d after %d nulls and %d zeros",
940	>	x, nulls.sum(), zeros.sum()));
941	>	};
942	>
943	>	Runnable adder = () -> { d.addFirst(0); d.addLast(42); };
944	>
945	>	runAsync(getter, adder);
946	>	}
947	>	}
948	>
949	>	/**
950	>	* Reverse direction variant of testBug8188900
951	>	*/
952	>	public void testBug8188900_reverse() {
953	>	final ThreadLocalRandom rnd = ThreadLocalRandom.current();
954	>	final LongAdder nulls = new LongAdder(), zeros = new LongAdder();
955	>	for (int n = expensiveTests ? 100_000 : 10; n--> 0; ) {
956	>	ConcurrentLinkedDeque<Integer> d = new ConcurrentLinkedDeque<>();
957	>
958	>	boolean peek = rnd.nextBoolean();
959	>	Runnable getter = () -> {
960	>	Integer x = peek ? d.peekLast() : d.pollLast();
961	>	if (x == null) nulls.increment();
962	>	else if (x == 0) zeros.increment();
963	>	else
964	>	throw new AssertionError(
965	>	String.format(
966	>	"unexpected value %d after %d nulls and %d zeros",
967	>	x, nulls.sum(), zeros.sum()));
968	>	};
969	>
970	>	Runnable adder = () -> { d.addLast(0); d.addFirst(42); };
971	>
972	>	runAsync(getter, adder);
973	>	}
974	>	}
975	>
976	>	<T> T chooseRandomly(T... choices) {
977	>	return choices[ThreadLocalRandom.current().nextInt(choices.length)];
978	>	}
979	>
980	>	/**
981	>	* Non-traversing Deque operations (that return null) are linearizable.
982	>	* Don't return null when the deque is observably never empty.
983	>	* https://bugs.openjdk.java.net/browse/JDK-8189387
984	>	* ant -Djsr166.expensiveTests=true -Djsr166.tckTestClass=ConcurrentLinkedDequeTest -Djsr166.methodFilter=testBug8189387 tck
985	>	*/
986	>	public void testBug8189387() {
987	>	final ThreadLocalRandom rnd = ThreadLocalRandom.current();
988	>	Object x = new Object();
989	>	for (int n = expensiveTests ? 100_000 : 10; n--> 0; ) {
990	>	ConcurrentLinkedDeque<Object> d = new ConcurrentLinkedDeque<>();
991	>	Runnable add = chooseRandomly(
992	>	() -> d.addFirst(x),
993	>	() -> d.offerFirst(x),
994	>	() -> d.addLast(x),
995	>	() -> d.offerLast(x));
996	>
997	>	Runnable get = chooseRandomly(
998	>	() -> assertFalse(d.isEmpty()),
999	>	() -> assertSame(x, d.peekFirst()),
1000	>	() -> assertSame(x, d.peekLast()),
1001	>	() -> assertSame(x, d.pollFirst()),
1002	>	() -> assertSame(x, d.pollLast()));
1003	>
1004	>	Runnable addRemove = chooseRandomly(
1005	>	() -> { d.addFirst(x); d.pollLast(); },
1006	>	() -> { d.offerFirst(x); d.removeFirst(); },
1007	>	() -> { d.offerLast(x); d.removeLast(); },
1008	>	() -> { d.addLast(x); d.pollFirst(); });
1009
1010	+	add.run();
1011	+	runAsync(get, addRemove);
1012	+	}
1013	+	}
1014		}

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