test/tck/ThreadLocalRandomTest.java

/*
 * Written by Doug Lea 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/
 */

import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;

import junit.framework.Test;
import junit.framework.TestSuite;

public class ThreadLocalRandomTest extends JSR166TestCase {

    public static void main(String[] args) {
        main(suite(), args);
    }
    public static Test suite() {
        return new TestSuite(ThreadLocalRandomTest.class);
    }

    /*
     * Testing coverage notes:
     *
     * We don't test randomness properties, but only that repeated
     * calls, up to NCALLS tries, produce at least one different
     * result.  For bounded versions, we sample various intervals
     * across multiples of primes.
     */

    // max numbers of calls to detect getting stuck on one value
    static final int NCALLS = 10000;

    // max sampled int bound
    static final int MAX_INT_BOUND = (1 << 28);

    // max sampled long bound
    static final long MAX_LONG_BOUND = (1L << 42);

    // Number of replications for other checks
    static final int REPS = 20;

    /**
     * setSeed throws UnsupportedOperationException
     */
    public void testSetSeed() {
        try {
            ThreadLocalRandom.current().setSeed(17);
            shouldThrow();
        } catch (UnsupportedOperationException success) {}
    }

    /**
     * Repeated calls to next (only accessible via reflection) produce
     * at least two distinct results, and repeated calls produce all
     * possible values.
     */
    public void testNext() throws ReflectiveOperationException {
        // Inhibit "An illegal reflective access operation has occurred"
        if (!testImplementationDetails) return;

        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        final java.lang.reflect.Method m;
        try {
            m = ThreadLocalRandom.class.getDeclaredMethod("next", int.class);
            m.setAccessible(true);
        } catch (SecurityException acceptable) {
            // Security manager may deny access
            return;
        } catch (Exception ex) {
            // jdk9 module system may deny access
            if (ex.getClass().getSimpleName()
                .equals("InaccessibleObjectException"))
                return;
            throw ex;
        }

        int i;
        {
            int val = new java.util.Random().nextInt(4);
            for (i = 0; i < NCALLS; i++) {
                int q = (int) m.invoke(rnd, new Object[] { 2 });
                if (val == q) break;
            }
            assertTrue(i < NCALLS);
        }

        {
            int r = (int) m.invoke(rnd, new Object[] { 3 });
            for (i = 0; i < NCALLS; i++) {
                int q = (int) m.invoke(rnd, new Object[] { 3 });
                assertTrue(q < (1<<3));
                if (r != q) break;
            }
            assertTrue(i < NCALLS);
        }
    }

    /**
     * Repeated calls to nextInt produce at least two distinct results
     */
    public void testNextInt() {
        int f = ThreadLocalRandom.current().nextInt();
        int i = 0;
        while (i < NCALLS && ThreadLocalRandom.current().nextInt() == f)
            ++i;
        assertTrue(i < NCALLS);
    }

    /**
     * Repeated calls to nextLong produce at least two distinct results
     */
    public void testNextLong() {
        long f = ThreadLocalRandom.current().nextLong();
        int i = 0;
        while (i < NCALLS && ThreadLocalRandom.current().nextLong() == f)
            ++i;
        assertTrue(i < NCALLS);
    }

    /**
     * Repeated calls to nextBoolean produce at least two distinct results
     */
    public void testNextBoolean() {
        boolean f = ThreadLocalRandom.current().nextBoolean();
        int i = 0;
        while (i < NCALLS && ThreadLocalRandom.current().nextBoolean() == f)
            ++i;
        assertTrue(i < NCALLS);
    }

    /**
     * Repeated calls to nextFloat produce at least two distinct results
     */
    public void testNextFloat() {
        float f = ThreadLocalRandom.current().nextFloat();
        int i = 0;
        while (i < NCALLS && ThreadLocalRandom.current().nextFloat() == f)
            ++i;
        assertTrue(i < NCALLS);
    }

    /**
     * Repeated calls to nextDouble produce at least two distinct results
     */
    public void testNextDouble() {
        double f = ThreadLocalRandom.current().nextDouble();
        int i = 0;
        while (i < NCALLS && ThreadLocalRandom.current().nextDouble() == f)
            ++i;
        assertTrue(i < NCALLS);
    }

    /**
     * Repeated calls to nextGaussian produce at least two distinct results
     */
    public void testNextGaussian() {
        double f = ThreadLocalRandom.current().nextGaussian();
        int i = 0;
        while (i < NCALLS && ThreadLocalRandom.current().nextGaussian() == f)
            ++i;
        assertTrue(i < NCALLS);
    }

    /**
     * nextInt(non-positive) throws IllegalArgumentException
     */
    public void testNextIntBoundNonPositive() {
        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        for (int bound : new int[] { 0, -17, Integer.MIN_VALUE }) {
            try {
                rnd.nextInt(bound);
                shouldThrow();
            } catch (IllegalArgumentException success) {}
        }
    }

    /**
     * nextInt(least >= bound) throws IllegalArgumentException
     */
    public void testNextIntBadBounds() {
        int[][] badBoundss = {
            { 17, 2 },
            { -42, -42 },
            { Integer.MAX_VALUE, Integer.MIN_VALUE },
        };
        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        for (int[] badBounds : badBoundss) {
            try {
                rnd.nextInt(badBounds[0], badBounds[1]);
                shouldThrow();
            } catch (IllegalArgumentException success) {}
        }
    }

    /**
     * nextInt(bound) returns 0 <= value < bound;
     * repeated calls produce at least two distinct results
     */
    public void testNextIntBounded() {
        // sample bound space across prime number increments
        for (int bound = 2; bound < MAX_INT_BOUND; bound += 524959) {
            int f = ThreadLocalRandom.current().nextInt(bound);
            assertTrue(0 <= f && f < bound);
            int i = 0;
            int j;
            while (i < NCALLS &&
                   (j = ThreadLocalRandom.current().nextInt(bound)) == f) {
                assertTrue(0 <= j && j < bound);
                ++i;
            }
            assertTrue(i < NCALLS);
        }
    }

    /**
     * nextInt(least, bound) returns least <= value < bound;
     * repeated calls produce at least two distinct results
     */
    public void testNextIntBounded2() {
        for (int least = -15485863; least < MAX_INT_BOUND; least += 524959) {
            for (int bound = least + 2; bound > least && bound < MAX_INT_BOUND; bound += 49979687) {
                int f = ThreadLocalRandom.current().nextInt(least, bound);
                assertTrue(least <= f && f < bound);
                int i = 0;
                int j;
                while (i < NCALLS &&
                       (j = ThreadLocalRandom.current().nextInt(least, bound)) == f) {
                    assertTrue(least <= j && j < bound);
                    ++i;
                }
                assertTrue(i < NCALLS);
            }
        }
    }

    /**
     * nextLong(non-positive) throws IllegalArgumentException
     */
    public void testNextLongBoundNonPositive() {
        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        for (long bound : new long[] { 0L, -17L, Long.MIN_VALUE }) {
            try {
                rnd.nextLong(bound);
                shouldThrow();
            } catch (IllegalArgumentException success) {}
        }
    }

    /**
     * nextLong(least >= bound) throws IllegalArgumentException
     */
    public void testNextLongBadBounds() {
        long[][] badBoundss = {
            { 17L, 2L },
            { -42L, -42L },
            { Long.MAX_VALUE, Long.MIN_VALUE },
        };
        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        for (long[] badBounds : badBoundss) {
            try {
                rnd.nextLong(badBounds[0], badBounds[1]);
                shouldThrow();
            } catch (IllegalArgumentException success) {}
        }
    }

    /**
     * nextLong(bound) returns 0 <= value < bound;
     * repeated calls produce at least two distinct results
     */
    public void testNextLongBounded() {
        for (long bound = 2; bound < MAX_LONG_BOUND; bound += 15485863) {
            long f = ThreadLocalRandom.current().nextLong(bound);
            assertTrue(0 <= f && f < bound);
            int i = 0;
            long j;
            while (i < NCALLS &&
                   (j = ThreadLocalRandom.current().nextLong(bound)) == f) {
                assertTrue(0 <= j && j < bound);
                ++i;
            }
            assertTrue(i < NCALLS);
        }
    }

    /**
     * nextLong(least, bound) returns least <= value < bound;
     * repeated calls produce at least two distinct results
     */
    public void testNextLongBounded2() {
        for (long least = -86028121; least < MAX_LONG_BOUND; least += 982451653L) {
            for (long bound = least + 2; bound > least && bound < MAX_LONG_BOUND; bound += Math.abs(bound * 7919)) {
                long f = ThreadLocalRandom.current().nextLong(least, bound);
                assertTrue(least <= f && f < bound);
                int i = 0;
                long j;
                while (i < NCALLS &&
                       (j = ThreadLocalRandom.current().nextLong(least, bound)) == f) {
                    assertTrue(least <= j && j < bound);
                    ++i;
                }
                assertTrue(i < NCALLS);
            }
        }
    }

    /**
     * nextDouble(non-positive) throws IllegalArgumentException
     */
    public void testNextDoubleBoundNonPositive() {
        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        double[] badBounds = {
            0.0d,
            -17.0d,
            -Double.MIN_VALUE,
            Double.NEGATIVE_INFINITY,
            Double.NaN,
        };
        for (double bound : badBounds) {
            try {
                rnd.nextDouble(bound);
                shouldThrow();
            } catch (IllegalArgumentException success) {}
        }
    }

    /**
     * nextDouble(least, bound) returns least <= value < bound;
     * repeated calls produce at least two distinct results
     */
    public void testNextDoubleBounded2() {
        for (double least = 0.0001; least < 1.0e20; least *= 8) {
            for (double bound = least * 1.001; bound < 1.0e20; bound *= 16) {
                double f = ThreadLocalRandom.current().nextDouble(least, bound);
                assertTrue(least <= f && f < bound);
                int i = 0;
                double j;
                while (i < NCALLS &&
                       (j = ThreadLocalRandom.current().nextDouble(least, bound)) == f) {
                    assertTrue(least <= j && j < bound);
                    ++i;
                }
                assertTrue(i < NCALLS);
            }
        }
    }

    /**
     * Different threads produce different pseudo-random sequences
     */
    public void testDifferentSequences() {
        // Don't use main thread's ThreadLocalRandom - it is likely to
        // be polluted by previous tests.
        final AtomicReference<ThreadLocalRandom> threadLocalRandom =
            new AtomicReference<>();
        final AtomicLong rand = new AtomicLong();

        Runnable getRandomState = new CheckedRunnable() {
            public void realRun() {
                ThreadLocalRandom current = ThreadLocalRandom.current();
                assertSame(current, ThreadLocalRandom.current());
                rand.set(current.nextLong());
                threadLocalRandom.set(current);
            }};

        awaitTermination(newStartedThread(getRandomState));
        long firstRand = rand.get();
        ThreadLocalRandom firstThreadLocalRandom = threadLocalRandom.get();
        assertNotNull(firstThreadLocalRandom);

        for (int i = 0; i < NCALLS; i++) {
            awaitTermination(newStartedThread(getRandomState));
            if (testImplementationDetails)
                // ThreadLocalRandom has been a singleton since jdk8.
                assertSame(firstThreadLocalRandom, threadLocalRandom.get());
            if (firstRand != rand.get())
                return;
        }
        fail("all threads generate the same pseudo-random sequence");
    }

    /**
     * Repeated calls to nextBytes produce at least values of different signs for every byte
     */
    public void testNextBytes() {
        ThreadLocalRandom rnd = ThreadLocalRandom.current();
        int n = rnd.nextInt(1, 20);
        byte[] bytes = new byte[n];
        outer:
        for (int i = 0; i < n; i++) {
            for (int tries = NCALLS; tries-->0; ) {
                byte before = bytes[i];
                rnd.nextBytes(bytes);
                byte after = bytes[i];
                if (after * before < 0)
                    continue outer;
            }
            fail("not enough variation in random bytes");
        }
    }

    /**
     * Filling an empty array with random bytes succeeds without effect.
     */
    public void testNextBytes_emptyArray() {
        ThreadLocalRandom.current().nextBytes(new byte[0]);
    }

    public void testNextBytes_nullArray() {
        try {
            ThreadLocalRandom.current().nextBytes(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

}
Revision:	1.30
Committed:	Wed Aug 12 17:39:43 2020 UTC (3 years, 8 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.29:	+8 -11 lines
Log Message:	testDifferentSequences: cleaner
#	Content
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/publicdomain/zero/1.0/
5	*/
6
7	import java.util.concurrent.ThreadLocalRandom;
8	import java.util.concurrent.atomic.AtomicLong;
9	import java.util.concurrent.atomic.AtomicReference;
10
11	import junit.framework.Test;
12	import junit.framework.TestSuite;
13
14	public class ThreadLocalRandomTest extends JSR166TestCase {
15
16	public static void main(String[] args) {
17	main(suite(), args);
18	}
19	public static Test suite() {
20	return new TestSuite(ThreadLocalRandomTest.class);
21	}
22
23	/*
24	* Testing coverage notes:
25	*
26	* We don't test randomness properties, but only that repeated
27	* calls, up to NCALLS tries, produce at least one different
28	* result. For bounded versions, we sample various intervals
29	* across multiples of primes.
30	*/
31
32	// max numbers of calls to detect getting stuck on one value
33	static final int NCALLS = 10000;
34
35	// max sampled int bound
36	static final int MAX_INT_BOUND = (1 << 28);
37
38	// max sampled long bound
39	static final long MAX_LONG_BOUND = (1L << 42);
40
41	// Number of replications for other checks
42	static final int REPS = 20;
43
44	/**
45	* setSeed throws UnsupportedOperationException
46	*/
47	public void testSetSeed() {
48	try {
49	ThreadLocalRandom.current().setSeed(17);
50	shouldThrow();
51	} catch (UnsupportedOperationException success) {}
52	}
53
54	/**
55	* Repeated calls to next (only accessible via reflection) produce
56	* at least two distinct results, and repeated calls produce all
57	* possible values.
58	*/
59	public void testNext() throws ReflectiveOperationException {
60	// Inhibit "An illegal reflective access operation has occurred"
61	if (!testImplementationDetails) return;
62
63	ThreadLocalRandom rnd = ThreadLocalRandom.current();
64	final java.lang.reflect.Method m;
65	try {
66	m = ThreadLocalRandom.class.getDeclaredMethod("next", int.class);
67	m.setAccessible(true);
68	} catch (SecurityException acceptable) {
69	// Security manager may deny access
70	return;
71	} catch (Exception ex) {
72	// jdk9 module system may deny access
73	if (ex.getClass().getSimpleName()
74	.equals("InaccessibleObjectException"))
75	return;
76	throw ex;
77	}
78
79	int i;
80	{
81	int val = new java.util.Random().nextInt(4);
82	for (i = 0; i < NCALLS; i++) {
83	int q = (int) m.invoke(rnd, new Object[] { 2 });
84	if (val == q) break;
85	}
86	assertTrue(i < NCALLS);
87	}
88
89	{
90	int r = (int) m.invoke(rnd, new Object[] { 3 });
91	for (i = 0; i < NCALLS; i++) {
92	int q = (int) m.invoke(rnd, new Object[] { 3 });
93	assertTrue(q < (1<<3));
94	if (r != q) break;
95	}
96	assertTrue(i < NCALLS);
97	}
98	}
99
100	/**
101	* Repeated calls to nextInt produce at least two distinct results
102	*/
103	public void testNextInt() {
104	int f = ThreadLocalRandom.current().nextInt();
105	int i = 0;
106	while (i < NCALLS && ThreadLocalRandom.current().nextInt() == f)
107	++i;
108	assertTrue(i < NCALLS);
109	}
110
111	/**
112	* Repeated calls to nextLong produce at least two distinct results
113	*/
114	public void testNextLong() {
115	long f = ThreadLocalRandom.current().nextLong();
116	int i = 0;
117	while (i < NCALLS && ThreadLocalRandom.current().nextLong() == f)
118	++i;
119	assertTrue(i < NCALLS);
120	}
121
122	/**
123	* Repeated calls to nextBoolean produce at least two distinct results
124	*/
125	public void testNextBoolean() {
126	boolean f = ThreadLocalRandom.current().nextBoolean();
127	int i = 0;
128	while (i < NCALLS && ThreadLocalRandom.current().nextBoolean() == f)
129	++i;
130	assertTrue(i < NCALLS);
131	}
132
133	/**
134	* Repeated calls to nextFloat produce at least two distinct results
135	*/
136	public void testNextFloat() {
137	float f = ThreadLocalRandom.current().nextFloat();
138	int i = 0;
139	while (i < NCALLS && ThreadLocalRandom.current().nextFloat() == f)
140	++i;
141	assertTrue(i < NCALLS);
142	}
143
144	/**
145	* Repeated calls to nextDouble produce at least two distinct results
146	*/
147	public void testNextDouble() {
148	double f = ThreadLocalRandom.current().nextDouble();
149	int i = 0;
150	while (i < NCALLS && ThreadLocalRandom.current().nextDouble() == f)
151	++i;
152	assertTrue(i < NCALLS);
153	}
154
155	/**
156	* Repeated calls to nextGaussian produce at least two distinct results
157	*/
158	public void testNextGaussian() {
159	double f = ThreadLocalRandom.current().nextGaussian();
160	int i = 0;
161	while (i < NCALLS && ThreadLocalRandom.current().nextGaussian() == f)
162	++i;
163	assertTrue(i < NCALLS);
164	}
165
166	/**
167	* nextInt(non-positive) throws IllegalArgumentException
168	*/
169	public void testNextIntBoundNonPositive() {
170	ThreadLocalRandom rnd = ThreadLocalRandom.current();
171	for (int bound : new int[] { 0, -17, Integer.MIN_VALUE }) {
172	try {
173	rnd.nextInt(bound);
174	shouldThrow();
175	} catch (IllegalArgumentException success) {}
176	}
177	}
178
179	/**
180	* nextInt(least >= bound) throws IllegalArgumentException
181	*/
182	public void testNextIntBadBounds() {
183	int[][] badBoundss = {
184	{ 17, 2 },
185	{ -42, -42 },
186	{ Integer.MAX_VALUE, Integer.MIN_VALUE },
187	};
188	ThreadLocalRandom rnd = ThreadLocalRandom.current();
189	for (int[] badBounds : badBoundss) {
190	try {
191	rnd.nextInt(badBounds[0], badBounds[1]);
192	shouldThrow();
193	} catch (IllegalArgumentException success) {}
194	}
195	}
196
197	/**
198	* nextInt(bound) returns 0 <= value < bound;
199	* repeated calls produce at least two distinct results
200	*/
201	public void testNextIntBounded() {
202	// sample bound space across prime number increments
203	for (int bound = 2; bound < MAX_INT_BOUND; bound += 524959) {
204	int f = ThreadLocalRandom.current().nextInt(bound);
205	assertTrue(0 <= f && f < bound);
206	int i = 0;
207	int j;
208	while (i < NCALLS &&
209	(j = ThreadLocalRandom.current().nextInt(bound)) == f) {
210	assertTrue(0 <= j && j < bound);
211	++i;
212	}
213	assertTrue(i < NCALLS);
214	}
215	}
216
217	/**
218	* nextInt(least, bound) returns least <= value < bound;
219	* repeated calls produce at least two distinct results
220	*/
221	public void testNextIntBounded2() {
222	for (int least = -15485863; least < MAX_INT_BOUND; least += 524959) {
223	for (int bound = least + 2; bound > least && bound < MAX_INT_BOUND; bound += 49979687) {
224	int f = ThreadLocalRandom.current().nextInt(least, bound);
225	assertTrue(least <= f && f < bound);
226	int i = 0;
227	int j;
228	while (i < NCALLS &&
229	(j = ThreadLocalRandom.current().nextInt(least, bound)) == f) {
230	assertTrue(least <= j && j < bound);
231	++i;
232	}
233	assertTrue(i < NCALLS);
234	}
235	}
236	}
237
238	/**
239	* nextLong(non-positive) throws IllegalArgumentException
240	*/
241	public void testNextLongBoundNonPositive() {
242	ThreadLocalRandom rnd = ThreadLocalRandom.current();
243	for (long bound : new long[] { 0L, -17L, Long.MIN_VALUE }) {
244	try {
245	rnd.nextLong(bound);
246	shouldThrow();
247	} catch (IllegalArgumentException success) {}
248	}
249	}
250
251	/**
252	* nextLong(least >= bound) throws IllegalArgumentException
253	*/
254	public void testNextLongBadBounds() {
255	long[][] badBoundss = {
256	{ 17L, 2L },
257	{ -42L, -42L },
258	{ Long.MAX_VALUE, Long.MIN_VALUE },
259	};
260	ThreadLocalRandom rnd = ThreadLocalRandom.current();
261	for (long[] badBounds : badBoundss) {
262	try {
263	rnd.nextLong(badBounds[0], badBounds[1]);
264	shouldThrow();
265	} catch (IllegalArgumentException success) {}
266	}
267	}
268
269	/**
270	* nextLong(bound) returns 0 <= value < bound;
271	* repeated calls produce at least two distinct results
272	*/
273	public void testNextLongBounded() {
274	for (long bound = 2; bound < MAX_LONG_BOUND; bound += 15485863) {
275	long f = ThreadLocalRandom.current().nextLong(bound);
276	assertTrue(0 <= f && f < bound);
277	int i = 0;
278	long j;
279	while (i < NCALLS &&
280	(j = ThreadLocalRandom.current().nextLong(bound)) == f) {
281	assertTrue(0 <= j && j < bound);
282	++i;
283	}
284	assertTrue(i < NCALLS);
285	}
286	}
287
288	/**
289	* nextLong(least, bound) returns least <= value < bound;
290	* repeated calls produce at least two distinct results
291	*/
292	public void testNextLongBounded2() {
293	for (long least = -86028121; least < MAX_LONG_BOUND; least += 982451653L) {
294	for (long bound = least + 2; bound > least && bound < MAX_LONG_BOUND; bound += Math.abs(bound * 7919)) {
295	long f = ThreadLocalRandom.current().nextLong(least, bound);
296	assertTrue(least <= f && f < bound);
297	int i = 0;
298	long j;
299	while (i < NCALLS &&
300	(j = ThreadLocalRandom.current().nextLong(least, bound)) == f) {
301	assertTrue(least <= j && j < bound);
302	++i;
303	}
304	assertTrue(i < NCALLS);
305	}
306	}
307	}
308
309	/**
310	* nextDouble(non-positive) throws IllegalArgumentException
311	*/
312	public void testNextDoubleBoundNonPositive() {
313	ThreadLocalRandom rnd = ThreadLocalRandom.current();
314	double[] badBounds = {
315	0.0d,
316	-17.0d,
317	-Double.MIN_VALUE,
318	Double.NEGATIVE_INFINITY,
319	Double.NaN,
320	};
321	for (double bound : badBounds) {
322	try {
323	rnd.nextDouble(bound);
324	shouldThrow();
325	} catch (IllegalArgumentException success) {}
326	}
327	}
328
329	/**
330	* nextDouble(least, bound) returns least <= value < bound;
331	* repeated calls produce at least two distinct results
332	*/
333	public void testNextDoubleBounded2() {
334	for (double least = 0.0001; least < 1.0e20; least *= 8) {
335	for (double bound = least * 1.001; bound < 1.0e20; bound *= 16) {
336	double f = ThreadLocalRandom.current().nextDouble(least, bound);
337	assertTrue(least <= f && f < bound);
338	int i = 0;
339	double j;
340	while (i < NCALLS &&
341	(j = ThreadLocalRandom.current().nextDouble(least, bound)) == f) {
342	assertTrue(least <= j && j < bound);
343	++i;
344	}
345	assertTrue(i < NCALLS);
346	}
347	}
348	}
349
350	/**
351	* Different threads produce different pseudo-random sequences
352	*/
353	public void testDifferentSequences() {
354	// Don't use main thread's ThreadLocalRandom - it is likely to
355	// be polluted by previous tests.
356	final AtomicReference<ThreadLocalRandom> threadLocalRandom =
357	new AtomicReference<>();
358	final AtomicLong rand = new AtomicLong();
359
360	Runnable getRandomState = new CheckedRunnable() {
361	public void realRun() {
362	ThreadLocalRandom current = ThreadLocalRandom.current();
363	assertSame(current, ThreadLocalRandom.current());
364	rand.set(current.nextLong());
365	threadLocalRandom.set(current);
366	}};
367
368	awaitTermination(newStartedThread(getRandomState));
369	long firstRand = rand.get();
370	ThreadLocalRandom firstThreadLocalRandom = threadLocalRandom.get();
371	assertNotNull(firstThreadLocalRandom);
372
373	for (int i = 0; i < NCALLS; i++) {
374	awaitTermination(newStartedThread(getRandomState));
375	if (testImplementationDetails)
376	// ThreadLocalRandom has been a singleton since jdk8.
377	assertSame(firstThreadLocalRandom, threadLocalRandom.get());
378	if (firstRand != rand.get())
379	return;
380	}
381	fail("all threads generate the same pseudo-random sequence");
382	}
383
384	/**
385	* Repeated calls to nextBytes produce at least values of different signs for every byte
386	*/
387	public void testNextBytes() {
388	ThreadLocalRandom rnd = ThreadLocalRandom.current();
389	int n = rnd.nextInt(1, 20);
390	byte[] bytes = new byte[n];
391	outer:
392	for (int i = 0; i < n; i++) {
393	for (int tries = NCALLS; tries-->0; ) {
394	byte before = bytes[i];
395	rnd.nextBytes(bytes);
396	byte after = bytes[i];
397	if (after * before < 0)
398	continue outer;
399	}
400	fail("not enough variation in random bytes");
401	}
402	}
403
404	/**
405	* Filling an empty array with random bytes succeeds without effect.
406	*/
407	public void testNextBytes_emptyArray() {
408	ThreadLocalRandom.current().nextBytes(new byte[0]);
409	}
410
411	public void testNextBytes_nullArray() {
412	try {
413	ThreadLocalRandom.current().nextBytes(null);
414	shouldThrow();
415	} catch (NullPointerException success) {}
416	}
417
418	}