/*

 * 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.Test;

import java.lang.ref.WeakReference;

import java.lang.invoke.MethodHandles;

import java.lang.invoke.VarHandle;

import java.util.ArrayDeque;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Collection;

import java.util.Collections;

import java.util.Iterator;

import java.util.List;

import java.util.NoSuchElementException;

import java.util.Queue;

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.CountDownLatch;

import java.util.concurrent.ThreadLocalRandom;

import java.util.concurrent.TimeUnit;

import java.util.function.BooleanSupplier;

@Test

public class WhiteBox {

    final ThreadLocalRandom rnd = ThreadLocalRandom.current();

    final MethodHandles.Lookup lookup = MethodHandles.lookup();

    final VarHandle ITRS, ITEMS, TAKEINDEX, PUTINDEX, COUNT, HEAD, NEXT, PREVTAKEINDEX;

    WhiteBox() throws ReflectiveOperationException {

        Class<?> qClass = ArrayBlockingQueue.class;

        Class<?> itrClass  = Class.forName(qClass.getName() + "$Itr");

        Class<?> itrsClass = Class.forName(qClass.getName() + "$Itrs");

        Class<?> nodeClass = Class.forName(itrsClass.getName() + "$Node");

        ITRS      = findVarHandle(qClass, "itrs", itrsClass);

        ITEMS     = findVarHandle(qClass, "items", Object[].class);

        TAKEINDEX = findVarHandle(qClass, "takeIndex", int.class);

        PUTINDEX  = findVarHandle(qClass, "putIndex", int.class);

        COUNT     = findVarHandle(qClass, "count", int.class);

        HEAD      = findVarHandle(itrsClass, "head", nodeClass);

        NEXT      = findVarHandle(nodeClass, "next", nodeClass);

        PREVTAKEINDEX = findVarHandle(itrClass, "prevTakeIndex", int.class);

    }

    VarHandle findVarHandle(Class<?> recv, String name, Class<?> type)

        throws ReflectiveOperationException {

        return MethodHandles.privateLookupIn(recv, lookup)

            .findVarHandle(recv, name, type);

    }

    Object itrs(ArrayBlockingQueue q) { return ITRS.get(q); }

    Object[] items(ArrayBlockingQueue q) { return (Object[]) ITEMS.get(q); }

    int takeIndex(ArrayBlockingQueue q) { return (int) TAKEINDEX.get(q); }

    int putIndex(ArrayBlockingQueue q) { return (int) PUTINDEX.get(q); }

    int count(ArrayBlockingQueue q) { return (int) COUNT.get(q); }

    Object head(Object itrs) { return HEAD.get(itrs); }

    Object next(Object node) { return NEXT.get(node); }

    int prevTakeIndex(Iterator itr) { return (int) PREVTAKEINDEX.get(itr); }

    boolean isDetached(Iterator it) {

        return prevTakeIndex(it) < 0;

    }

    void assertIteratorExhausted(Iterator it) {

        if (rnd.nextBoolean()) {

            assertTrue(!it.hasNext());

            assertTrue(isDetached(it));

        }

        if (rnd.nextBoolean()) {

            it.forEachRemaining(e -> { throw new AssertionError(); });

            assertTrue(isDetached(it));

        }

        if (rnd.nextBoolean())

            try { it.next(); fail("should throw"); }

            catch (NoSuchElementException success) {}

    }

    List<Iterator> trackedIterators(ArrayBlockingQueue q) {

        List<Iterator> its = new ArrayList<>();

        Object itrs = itrs(q);

        if (itrs != null) {

            for (Object p = head(itrs); p != null; p = next(p))

                its.add(((WeakReference<Iterator>)(p)).get());

            Collections.reverse(its);

        }

        return its;

    }

    List<Iterator> attachedIterators(ArrayBlockingQueue q) {

        List<Iterator> its = new ArrayList<>();

        Object itrs = itrs(q);

        if (itrs != null) {

            for (Object p = head(itrs); p != null; p = next(p)) {

                Iterator it = ((WeakReference<Iterator>)(p)).get();

                if (it != null && !isDetached(it))

                    its.add(it);

            }

            Collections.reverse(its);

        }

        return its;

    }

    void assertRemoveThrowsISE(Iterator it) {

        if (rnd.nextBoolean())

            try { it.remove(); fail("should throw"); }

            catch (IllegalStateException success) {}

    }

    void assertRemoveHasNoEffect(Iterator it, Collection c) {

        if (rnd.nextBoolean()) {

            int size = c.size();

            it.remove(); // no effect

            assertEquals(c.size(), size);

            assertRemoveThrowsISE(it);

        }

    }

    void checkIterationSanity(Queue q) {

        if (rnd.nextBoolean())

            return;

        int size = q.size();

        Object[] a = q.toArray();

        Object[] b = new Object[size+2];

        Arrays.fill(b, Boolean.TRUE);

        Object[] c = q.toArray(b);

        assertEquals(a.length, size);

        assertSame(b, c);

        assertNull(b[size]);

        assertSame(b[size+1], Boolean.TRUE);

        assertEquals(q.toString(), Arrays.toString(a));

        Integer[] xx = null, yy = null;

        if (size > 0) {

            xx = new Integer[size - 1];

            Arrays.fill(xx, 42);

            yy = ((Queue<Integer>)q).toArray(xx);

            for (Integer zz : xx)

                assertEquals(42, (int) zz);

        }

        Iterator it = q.iterator();

        for (int i = 0; i < size; i++) {

            if (rnd.nextBoolean()) assertTrue(it.hasNext());

            Object x = it.next();

            assertSame(x, a[i]);

            assertSame(x, b[i]);

        }

        if (rnd.nextBoolean()) assertTrue(!it.hasNext());

    }

    /**

     * Instead of having putIndex (and takeIndex) at the initial

     * default of 0, move them to a random location.

     */

    void randomizePutIndex(ArrayBlockingQueue q) {

        assertTrue(q.isEmpty());

        int capacity = q.remainingCapacity();

        int n = rnd.nextInt(capacity + 1);

        int putIndex = putIndex(q);

        for (int i = n; i-->0; ) q.add(Boolean.TRUE);

        for (int i = n; i-->0; ) q.remove();

        assertEquals(putIndex(q), (putIndex + n) % items(q).length);

    }

    /** No guarantees, but effective in practice. */

    static void forceFullGc() {

        CountDownLatch finalizeDone = new CountDownLatch(1);

        WeakReference<?> ref = new WeakReference<Object>(new Object() {

            protected void finalize() { finalizeDone.countDown(); }});

        try {

            for (int i = 0; i < 10; i++) {

                System.gc();

                if (finalizeDone.await(1L, TimeUnit.SECONDS) && ref.get() == null) {

                    System.runFinalization(); // try to pick up stragglers

                    return;

                }

            }

        } catch (InterruptedException unexpected) {

            throw new AssertionError("unexpected InterruptedException");

        }

        throw new AssertionError("failed to do a \"full\" gc");

    }

    static void gcAwait(BooleanSupplier s) {

        for (int i = 0; i < 10; i++) {

            if (s.getAsBoolean())

                return;

            forceFullGc();

        }

        throw new AssertionError("failed to satisfy condition");

    }

    public void clear_willClearItrs() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(2, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        List<Iterator> its = new ArrayList<>();

        for (int i = 0; i < capacity; i++)

            assertTrue(q.add(i));

        assertNull(itrs(q));

        for (int i = 0; i < capacity; i++) {

            its.add(q.iterator());

            assertEquals(trackedIterators(q), its);

            q.poll();

            q.add(capacity + i);

        }

        q.clear();

        assertNull(itrs(q));

        int j = 0;

        for (Iterator it : its) {

            assertTrue(isDetached(it));

            if (rnd.nextBoolean()) assertTrue(it.hasNext());

            if (rnd.nextBoolean()) {

                assertEquals(it.next(), j);

                assertIteratorExhausted(it);

            }

            j++;

        }

    }

    public void queueEmptyingWillClearItrs() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(2, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        List<Iterator> its = new ArrayList<>();

        for (int i = 0; i < capacity; i++)

            q.add(i);

        assertNull(itrs(q));

        for (int i = 0; i < capacity; i++) {

            its.add(q.iterator());

            assertEquals(trackedIterators(q), its);

            q.poll();

            q.add(capacity+i);

        }

        for (int i = 0; i < capacity; i++)

            q.poll();

        assertNull(itrs(q));

        int j = 0;

        for (Iterator it : its) {

            assertTrue(isDetached(it));

            if (rnd.nextBoolean()) assertTrue(it.hasNext());

            if (rnd.nextBoolean()) {

                assertEquals(it.next(), j);

                assertIteratorExhausted(it);

            }

            j++;

        }

    }

    public void advancing2CyclesWillRemoveIterators() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(2, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        List<Iterator> its = new ArrayList<>();

        for (int i = 0; i < capacity; i++)

            q.add(i);

        assertNull(itrs(q));

        for (int i = capacity; i < 3 * capacity; i++) {

            its.add(q.iterator());

            assertEquals(trackedIterators(q), its);

            q.poll();

            q.add(i);

        }

        for (int i = 3 * capacity; i < 4 * capacity; i++) {

            assertEquals(trackedIterators(q), its.subList(capacity,2*capacity));

            q.poll();

            q.add(i);

        }

        assertNull(itrs(q));

        int j = 0;

        for (Iterator it : its) {

            assertTrue(isDetached(it));

            if (rnd.nextBoolean()) assertTrue(it.hasNext());

            if (rnd.nextBoolean()) {

                assertEquals(it.next(), j);

                assertIteratorExhausted(it);

            }

            j++;

        }

    }

    /**

     * Interior removal of elements used by an iterator will cause it

     * to be untracked.

     */

    public void interiorRemovalOfElementsUsedByIterator() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(10, 20);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        q.add(0);

        for (int i = 1; i < 2 * capacity; i++) {

            q.add(i);

            Integer[] elts = { -1, -2, -3 };

            for (Integer elt : elts) q.add(elt);

            assertEquals(q.remove(), i - 1);

            Iterator it = q.iterator();

            assertEquals(it.next(), i);

            assertEquals(it.next(), elts[0]);

            Collections.shuffle(Arrays.asList(elts));

            assertTrue(q.remove(elts[0]));

            assertTrue(q.remove(elts[1]));

            assertEquals(trackedIterators(q), Collections.singletonList(it));

            assertTrue(q.remove(elts[2]));

            assertNull(itrs(q));

            assertEquals(it.next(), -2);

            assertIteratorExhausted(it);

            assertTrue(isDetached(it));

        }

    }

    public void iteratorsOnEmptyQueue() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(1, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        for (int i = 0; i < 4; i++) {

            Iterator it = q.iterator();

            assertNull(itrs(q));

            assertIteratorExhausted(it);

            assertTrue(isDetached(it));

            assertRemoveThrowsISE(it);

        }

    }

    public void interiorRemovalOfIteratorsLastElement() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(3, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        List<Iterator> its = new ArrayList<>();

        for (int i = 0; i < capacity; i++)

            q.add(i);

        for (int i = 0; i < capacity; i++) {

            Iterator it = q.iterator();

            its.add(it);

            for (int j = 0; j < i; j++)

                assertEquals(j, it.next());

            assertEquals(attachedIterators(q), its);

        }

        q.remove(capacity - 1);

        assertEquals(attachedIterators(q), its);

        for (int i = 1; i < capacity - 1; i++) {

            q.remove(capacity - i - 1);

            Iterator it = its.get(capacity - i);

            assertTrue(isDetached(it));

            assertEquals(attachedIterators(q), its.subList(0, capacity - i));

            if (rnd.nextBoolean()) assertTrue(it.hasNext());

            assertEquals(it.next(), capacity - i);

            assertIteratorExhausted(it);

        }

        assertEquals(attachedIterators(q), its.subList(0, 2));

        q.remove(0);

        assertTrue(q.isEmpty());

        assertNull(itrs(q));

        Iterator it = its.get(0);

        assertEquals(it.next(), 0);

        assertRemoveHasNoEffect(it, q);

        assertIteratorExhausted(it);

        assertTrue(isDetached(it));

        assertRemoveHasNoEffect(its.get(1), q);

    }

    /**

     * Checks "interior" removal of alternating elements, straddling 2 cycles

     */

    public void interiorRemovalOfAlternatingElements() {

        boolean fair = rnd.nextBoolean();

        int capacity = 2 * rnd.nextInt(2, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        List<Iterator> its = new ArrayList<>();

        // Move takeIndex to middle

        for (int i = 0; i < capacity/2; i++) {

            assertTrue(q.add(i));

            assertEquals(q.poll(), i);

        }

        assertEquals(takeIndex(q), capacity/2);

        for (int i = 0; i < capacity; i++)

            q.add(i);

        for (int i = 0; i < capacity; i++) {

            Iterator it = q.iterator();

            its.add(it);

            for (int j = 0; j < i; j++)

                assertEquals(j, it.next());

            assertEquals(attachedIterators(q), its);

        }

        // Remove all even elements, in either direction, using

        // q.remove(), or iterator.remove()

        switch (rnd.nextInt(3)) {

        case 0:

            for (int i = 0; i < capacity; i+=2) assertTrue(q.remove(i));

            break;

        case 1:

            for (int i = capacity - 2; i >= 0; i-=2) assertTrue(q.remove(i));

            break;

        case 2:

            Iterator it = q.iterator();

            while (it.hasNext()) {

                int i = (Integer) it.next();

                if ((i & 1) == 0)

                    it.remove();

            }

            break;

        default: throw new AssertionError();

        }

        assertEquals(attachedIterators(q), its);

        for (int i = 0; i < capacity; i++) {

            Iterator it = its.get(i);

            boolean even = ((i & 1) == 0);

            if (even) {

                if (rnd.nextBoolean()) assertTrue(it.hasNext());

                assertEquals(i, it.next());

                for (int j = i+1; j < capacity; j += 2)

                    assertEquals(j, it.next());

                assertTrue(!isDetached(it));

                assertTrue(!it.hasNext());

                assertTrue(isDetached(it));

            } else { /* odd */

                if (rnd.nextBoolean()) assertTrue(it.hasNext());

                assertRemoveHasNoEffect(it, q);

                assertEquals(i, it.next());

                for (int j = i+2; j < capacity; j += 2)

                    assertEquals(j, it.next());

                assertTrue(!isDetached(it));

                assertTrue(!it.hasNext());

                assertTrue(isDetached(it));

            }

        }

        assertEquals(trackedIterators(q), Collections.emptyList());

        assertNull(itrs(q));

    }

    public void garbageCollectionOfUnreachableIterators() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(1, 10);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        List<Iterator> its = new ArrayList<>();

        for (int i = 0; i < capacity; i++) q.add(i);

        for (int i = 0; i < capacity; i++) its.add(q.iterator());

        assertEquals(attachedIterators(q), its);

        its = null;

        gcAwait(() -> {

            List<Iterator> trackedIterators = trackedIterators(q);

            assertEquals(trackedIterators.size(), capacity);

            for (Iterator x : trackedIterators)

                if (x != null) return false;

            return true;

        });

        Iterator it = q.iterator(); //

        assertEquals(trackedIterators(q), Collections.singletonList(it));

    }

    public void garbageCollectionOfUnreachableIteratorsWithRandomlyRetainedSubset() {

        boolean fair = rnd.nextBoolean();

        int capacity = rnd.nextInt(10, 20);

        ArrayBlockingQueue q = new ArrayBlockingQueue(capacity, fair);

        randomizePutIndex(q);

        List<Iterator> its = new ArrayList<>();

        List<Iterator> retained = new ArrayList<>();

        final int size = 1 + rnd.nextInt(capacity);

        for (int i = 0; i < size; i++) q.add(i);

        for (int i = 0; i < size; i++) its.add(q.iterator());

        assertEquals(attachedIterators(q), its);

        // Leave sufficient gaps in retained

        for (int i = 0; i < size; i+= 2+rnd.nextInt(3))

            retained.add(its.get(i));

        its = null;

        gcAwait(() -> {

            List<Iterator> trackedIterators = trackedIterators(q);

            assertEquals(trackedIterators.size(), size);

            for (Iterator it : trackedIterators)

                if ((it != null) ^ retained.contains(it)) return false;

            return true;

        });

        Iterator it = q.iterator(); // trigger another sweep

        retained.add(it);

        assertEquals(trackedIterators(q), retained);

    }

    /**

     * Checks incremental sweeping of unreachable iterators.

     * Excessively white box?!

     */

    public void incrementalSweepingOfUnreachableIterators() {

        boolean fair = rnd.nextBoolean();