Add the recording queue utility.

/*

 * Copyright (C) 2019 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.android.testutils

import java.util.concurrent.TimeUnit

import java.util.concurrent.locks.Condition

import java.util.concurrent.locks.ReentrantLock

import kotlin.concurrent.withLock

/**

 * A List that additionally offers the ability to append via the add() method, and to retrieve

 * an element by its index optionally waiting for it to become available.

 */

interface TrackRecord<E> : List<E> {

    /**

     * Adds an element to this queue, waking up threads waiting for one. Returns the element.

     */

    fun add(e: E): TrackRecord<E>

    /**

     * Returns the first element after {@param pos}, possibly blocking until one is available, or

     * null if no such element can be found within the timeout.

     * If a predicate is given, only elements matching the predicate are returned.

     *

     * @param timeoutMs how long, in milliseconds, to wait at most (best effort approximation).

     * @param pos the position at which to start polling.

     * @param predicate an optional predicate to filter elements to be returned.

     * @return an element matching the predicate, or null if timeout.

     */

    fun poll(timeoutMs: Long, pos: Int, predicate: (E) -> Boolean = { true }): E?

}

/**

 * A thread-safe implementation of TrackRecord that is backed by an ArrayList.

 *

 * This class also supports the creation of a read-head for easier single-thread access.

 * Refer to the documentation of {@link ArrayTrackRecord.ReadHead}.

 */

class ArrayTrackRecord<E> : TrackRecord<E> {

    private val lock = ReentrantLock()

    private val condition = lock.newCondition()

    // Backing store. This stores the elements in this ArrayTrackRecord.

    private val elements = ArrayList<E>()

    // The list iterator for RecordingQueue iterates over a snapshot of the collection at the

    // time the operator is created. Because TrackRecord is only ever mutated by appending,

    // that makes this iterator thread-safe as it sees an effectively immutable List.

    class ArrayTrackRecordIterator<E>(

        private val list: ArrayList<E>,

        start: Int,

        private val end: Int

    ) : ListIterator<E> {

        var index = start

        override fun hasNext() = index < end

        override fun next() = list[index++]

        override fun hasPrevious() = index > 0

        override fun nextIndex() = index + 1

        override fun previous() = list[--index]

        override fun previousIndex() = index - 1

    }

    // List<E> implementation

    override val size get() = lock.withLock { elements.size }

    override fun contains(element: E) = lock.withLock { elements.contains(element) }

    override fun containsAll(elements: Collection<E>) = lock.withLock {

        this.elements.containsAll(elements)

    }

    override operator fun get(index: Int) = lock.withLock { elements[index] }

    override fun indexOf(element: E): Int = lock.withLock { elements.indexOf(element) }

    override fun lastIndexOf(element: E): Int = lock.withLock { elements.lastIndexOf(element) }

    override fun isEmpty() = lock.withLock { elements.isEmpty() }

    override fun listIterator(index: Int) = ArrayTrackRecordIterator(elements, index, size)

    override fun listIterator() = listIterator(0)

    override fun iterator() = listIterator()

    override fun subList(fromIndex: Int, toIndex: Int): List<E> = lock.withLock {

        elements.subList(fromIndex, toIndex)

    }

    // TrackRecord<E> implementation

    override fun add(e: E): ArrayTrackRecord<E> {

        lock.withLock {

            elements.add(e)

            condition.signalAll()

        }

        return this

    }

    override fun poll(timeoutMs: Long, pos: Int, predicate: (E) -> Boolean) = lock.withLock {

        elements.getOrNull(pollForIndexReadLocked(timeoutMs, pos, predicate))

    }

    // For convenience

    fun getOrNull(pos: Int, predicate: (E) -> Boolean) = lock.withLock {

        if (pos < 0 || pos > size) null else elements.subList(pos, size).find(predicate)

    }

    // Returns the index of the next element whose position is >= pos matching the predicate, if

    // necessary waiting until such a time that such an element is available, with a timeout.

    // If no such element is found within the timeout -1 is returned.

    private fun pollForIndexReadLocked(timeoutMs: Long, pos: Int, predicate: (E) -> Boolean): Int {

        val deadline = System.currentTimeMillis() + timeoutMs

        var index = pos

        do {

            while (index < elements.size) {

                if (predicate(elements[index])) return index

                ++index

            }

        } while (condition.await(deadline - System.currentTimeMillis()))

        return -1

    }

    /**

     * Returns a ReadHead over this ArrayTrackRecord. The returned ReadHead is tied to the

     * current thread.

     */

    fun newReadHead() = ReadHead()

    /**

     * ReadHead is an object that helps users of ArrayTrackRecord keep track of how far

     * it has read this far in the ArrayTrackRecord. A ReadHead is always associated with

     * a single instance of ArrayTrackRecord. Multiple ReadHeads can be created and used

     * on the same instance of ArrayTrackRecord concurrently, and the ArrayTrackRecord

     * instance can also be used concurrently. ReadHead maintains the current index that is

     * the next to be read, and calls this the "mark".

     *

     * A ReadHead delegates all TrackRecord methods to its associated ArrayTrackRecord, and

     * inherits its thread-safe properties. However, the additional methods that ReadHead

     * offers on top of TrackRecord do not share these properties and can only be used by

     * the thread that created the ReadHead. This is because by construction it does not

     * make sense to use a ReadHead on multiple threads concurrently (see below for details).

     *

     * In a ReadHead, {@link poll(Long, (E) -> Boolean)} works similarly to a LinkedBlockingQueue.

     * It can be called repeatedly and will return the elements as they arrive.

     *

     * Intended usage looks something like this :

     * val TrackRecord<MyObject> record = ArrayTrackRecord().newReadHead()

     * Thread().start {

     *   // do stuff

     *   record.add(something)

     *   // do stuff

     * }

     *

     * val obj1 = record.poll(timeout)

     * // do something with obj1

     * val obj2 = record.poll(timeout)

     * // do something with obj2

     *

     * The point is that the caller does not have to track the mark like it would have to if

     * it was using ArrayTrackRecord directly.

     *

     * Note that if multiple threads were using poll() concurrently on the same ReadHead, what

     * happens to the mark and the return values could be well defined, but it could not

     * be useful because there is no way to provide either a guarantee not to skip objects nor

     * a guarantee about the mark position at the exit of poll(). This is even more true in the

     * presence of a predicate to filter returned elements, because one thread might be

     * filtering out the events the other is interested in.

     * Instead, this use case is supported by creating multiple ReadHeads on the same instance

     * of ArrayTrackRecord. Each ReadHead is then guaranteed to see all events always and

     * guarantees are made on the value of the mark upon return. {@see poll(Long, (E) -> Boolean)}

     * for details. Be careful to create each ReadHead on the thread it is meant to be used on.

     *

     * Users of a ReadHead can ask for the current position of the mark at any time. This mark

     * can be used later to replay the history of events either on this ReadHead, on the associated

     * ArrayTrackRecord or on another ReadHead associated with the same ArrayTrackRecord. It

     * might look like this in the reader thread :

     *

     * val markAtStart = record.mark

     * // Start processing interesting events

     * while (val element = record.poll(timeout) { it.isInteresting() }) {

     *   // Do something with element

     * }

     * // Look for stuff that happened while searching for interesting events

     * val firstElementReceived = record.getOrNull(markAtStart)

     * val firstSpecialElement = record.getOrNull(markAtStart) { it.isSpecial() }

     * // Get the first special element since markAtStart, possibly blocking until one is available

     * val specialElement = record.poll(timeout, markAtStart) { it.isSpecial() }

     */

    inner class ReadHead : TrackRecord<E> by this@ArrayTrackRecord {

        private val owningThread = Thread.currentThread()

        private var readHead = 0

        /**

         * @return the current value of the mark.

         */

        val mark get() = readHead.also { checkThread() }

        private fun checkThread() = check(Thread.currentThread() == owningThread) {

            "Must be called by the thread that created this object"

        }

        /**

         * Returns the first element after the mark, optionally blocking until one is available, or

         * null if no such element can be found within the timeout.

         * If a predicate is given, only elements matching the predicate are returned.

         *

         * Upon return the mark will be set to immediately after the returned element, or after

         * the last element in the queue if null is returned. This means this method will always

         * skip elements that do not match the predicate, even if it returns null.

         *

         * This method can only be used by the thread that created this ManagedRecordingQueue.

         * If used on another thread, this throws IllegalStateException.

         *

         * @param timeoutMs how long, in milliseconds, to wait at most (best effort approximation).

         * @param predicate an optional predicate to filter elements to be returned.

         * @return an element matching the predicate, or null if timeout.

         */

        fun poll(timeoutMs: Long, predicate: (E) -> Boolean = { true }): E? {

            checkThread()

            lock.withLock {

                val index = pollForIndexReadLocked(timeoutMs, readHead, predicate)

                readHead = if (index < 0) size else index + 1

                return getOrNull(index)

            }

        }

        /**

         * Returns the first element after the mark or null. This never blocks.

         *

         * This method can only be used by the thread that created this ManagedRecordingQueue.

         * If used on another thread, this throws IllegalStateException.

         */

        fun peek(): E? = getOrNull(readHead).also { checkThread() }

    }

}

// Private helper

private fun Condition.await(timeoutMs: Long) = this.await(timeoutMs, TimeUnit.MILLISECONDS)

/*

 * Copyright (C) 2019 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package android.net.testutils

import com.android.testutils.ArrayTrackRecord

import org.junit.Test

import org.junit.runner.RunWith

import org.junit.runners.JUnit4

import kotlin.test.assertEquals

import kotlin.test.assertFailsWith

import kotlin.test.assertFalse

import kotlin.test.assertNotEquals

import kotlin.test.assertNull

import kotlin.test.assertTrue

import kotlin.test.fail

val TEST_VALUES = listOf(4, 13, 52, 94, 41, 68, 11, 13, 51, 0, 91, 94, 33, 98, 14)

const val ABSENT_VALUE = 2

@RunWith(JUnit4::class)

class TrackRecordTest {

    @Test

    fun testAddAndSizeAndGet() {

        val repeats = 22 // arbitrary

        val record = ArrayTrackRecord<Int>()

        assertEquals(0, record.size)

        repeat(repeats) { i -> record.add(i + 2) }

        assertEquals(repeats, record.size)

        record.add(2)

        assertEquals(repeats + 1, record.size)

        assertEquals(11, record[9])

        assertEquals(11, record.getOrNull(9))

        assertEquals(2, record[record.size - 1])

        assertEquals(2, record.getOrNull(record.size - 1))

        assertFailsWith<IndexOutOfBoundsException> { record[800] }

        assertFailsWith<IndexOutOfBoundsException> { record[-1] }

        assertFailsWith<IndexOutOfBoundsException> { record[repeats + 1] }

        assertNull(record.getOrNull(800))

        assertNull(record.getOrNull(-1))

        assertNull(record.getOrNull(repeats + 1))

        assertNull(record.getOrNull(800) { true })

        assertNull(record.getOrNull(-1) { true })

        assertNull(record.getOrNull(repeats + 1) { true })

    }

    @Test

    fun testIndexOf() {

        val record = ArrayTrackRecord<Int>()

        TEST_VALUES.forEach { record.add(it) }

        with(record) {

            assertEquals(9, indexOf(0))

            assertEquals(9, lastIndexOf(0))

            assertEquals(1, indexOf(13))

            assertEquals(7, lastIndexOf(13))

            assertEquals(3, indexOf(94))

            assertEquals(11, lastIndexOf(94))

            assertEquals(-1, indexOf(ABSENT_VALUE))

            assertEquals(-1, lastIndexOf(ABSENT_VALUE))

        }

    }

    @Test

    fun testContains() {

        val record = ArrayTrackRecord<Int>()

        TEST_VALUES.forEach { record.add(it) }

        TEST_VALUES.forEach { assertTrue(record.contains(it)) }

        assertFalse(record.contains(ABSENT_VALUE))

        assertTrue(record.containsAll(TEST_VALUES))

        assertTrue(record.containsAll(TEST_VALUES.sorted()))

        assertTrue(record.containsAll(TEST_VALUES.sortedDescending()))

        assertTrue(record.containsAll(TEST_VALUES.distinct()))

        assertTrue(record.containsAll(TEST_VALUES.subList(0, TEST_VALUES.size / 2)))

        assertTrue(record.containsAll(TEST_VALUES.subList(0, TEST_VALUES.size / 2).sorted()))

        assertTrue(record.containsAll(listOf()))

        assertFalse(record.containsAll(listOf(ABSENT_VALUE)))

        assertFalse(record.containsAll(TEST_VALUES + listOf(ABSENT_VALUE)))

    }

    @Test

    fun testEmpty() {

        val record = ArrayTrackRecord<Int>()

        assertTrue(record.isEmpty())

        record.add(1)

        assertFalse(record.isEmpty())

    }

    @Test

    fun testIterate() {

        val record = ArrayTrackRecord<Int>()

        record.forEach { fail("Expected nothing to iterate") }

        TEST_VALUES.forEach { record.add(it) }

        // zip relies on the iterator (this calls extension function Iterable#zip(Iterable))

        record.zip(TEST_VALUES).forEach { assertEquals(it.first, it.second) }

        // Also test reverse iteration (to test hasPrevious() and friends)

        record.reversed().zip(TEST_VALUES.reversed()).forEach { assertEquals(it.first, it.second) }

    }

    @Test

    fun testIteratorIsSnapshot() {

        val record = ArrayTrackRecord<Int>()

        TEST_VALUES.forEach { record.add(it) }

        val iterator = record.iterator()

        val expectedSize = record.size

        record.add(ABSENT_VALUE)

        record.add(ABSENT_VALUE)

        var measuredSize = 0

        iterator.forEach {

            ++measuredSize

            assertNotEquals(ABSENT_VALUE, it)

        }

        assertEquals(expectedSize, measuredSize)

    }

    @Test

    fun testSublist() {

        val record = ArrayTrackRecord<Int>()

        TEST_VALUES.forEach { record.add(it) }

        assertEquals(record.subList(3, record.size - 3),

                TEST_VALUES.subList(3, TEST_VALUES.size - 3))

    }

    /**

     * // TODO : add the following tests.

     * Test poll()

     *   - Put stuff, check that it's returned immediately

     *   - Check that it waits and times out

     *   - Check that it waits and finds the stuff added through the timeout

     *   - Put stuff, check that it's returned immediately when it matches the predicate

     *   - Check that it immediately finds added stuff that matches

     * Test ReadHead#poll()

     *   - All of the above, and:

     *   - Put stuff, check that it timeouts when it doesn't match the predicate, and the read head

     *     has advanced

     *   - Check that it immediately advances the read head

     * Test ReadHead#peek()

     */

}