1 /*
2 * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
3 */
4
5 package kotlinx.coroutines.test
6
7 import kotlinx.atomicfu.*
8 import kotlinx.coroutines.*
9 import kotlinx.coroutines.channels.*
10 import kotlinx.coroutines.channels.Channel.Factory.CONFLATED
11 import kotlinx.coroutines.internal.*
12 import kotlinx.coroutines.selects.*
13 import kotlin.coroutines.*
14 import kotlin.jvm.*
15 import kotlin.time.*
16
17 /**
18 * This is a scheduler for coroutines used in tests, providing the delay-skipping behavior.
19 *
20 * [Test dispatchers][TestDispatcher] are parameterized with a scheduler. Several dispatchers can share the
21 * same scheduler, in which case their knowledge about the virtual time will be synchronized. When the dispatchers
22 * require scheduling an event at a later point in time, they notify the scheduler, which will establish the order of
23 * the tasks.
24 *
25 * The scheduler can be queried to advance the time (via [advanceTimeBy]), run all the scheduled tasks advancing the
26 * virtual time as needed (via [advanceUntilIdle]), or run the tasks that are scheduled to run as soon as possible but
27 * haven't yet been dispatched (via [runCurrent]).
28 */
29 @ExperimentalCoroutinesApi
30 public class TestCoroutineScheduler : AbstractCoroutineContextElement(TestCoroutineScheduler),
31 CoroutineContext.Element {
32
33 /** @suppress */
34 public companion object Key : CoroutineContext.Key<TestCoroutineScheduler>
35
36 /** This heap stores the knowledge about which dispatchers are interested in which moments of virtual time. */
37 // TODO: all the synchronization is done via a separate lock, so a non-thread-safe priority queue can be used.
38 private val events = ThreadSafeHeap<TestDispatchEvent<Any>>()
39
40 /** Establishes that [currentTime] can't exceed the time of the earliest event in [events]. */
41 private val lock = SynchronizedObject()
42
43 /** This counter establishes some order on the events that happen at the same virtual time. */
44 private val count = atomic(0L)
45
46 /** The current virtual time in milliseconds. */
47 @ExperimentalCoroutinesApi
48 public var currentTime: Long = 0
<lambda>null49 get() = synchronized(lock) { field }
50 private set
51
52 /** A channel for notifying about the fact that a dispatch recently happened. */
53 private val dispatchEvents: Channel<Unit> = Channel(CONFLATED)
54
55 /**
56 * Registers a request for the scheduler to notify [dispatcher] at a virtual moment [timeDeltaMillis] milliseconds
57 * later via [TestDispatcher.processEvent], which will be called with the provided [marker] object.
58 *
59 * Returns the handler which can be used to cancel the registration.
60 */
registerEventnull61 internal fun <T : Any> registerEvent(
62 dispatcher: TestDispatcher,
63 timeDeltaMillis: Long,
64 marker: T,
65 context: CoroutineContext,
66 isCancelled: (T) -> Boolean
67 ): DisposableHandle {
68 require(timeDeltaMillis >= 0) { "Attempted scheduling an event earlier in time (with the time delta $timeDeltaMillis)" }
69 checkSchedulerInContext(this, context)
70 val count = count.getAndIncrement()
71 val isForeground = context[BackgroundWork] === null
72 return synchronized(lock) {
73 val time = addClamping(currentTime, timeDeltaMillis)
74 val event = TestDispatchEvent(dispatcher, count, time, marker as Any, isForeground) { isCancelled(marker) }
75 events.addLast(event)
76 /** can't be moved above: otherwise, [onDispatchEvent] could consume the token sent here before there's
77 * actually anything in the event queue. */
78 sendDispatchEvent(context)
79 DisposableHandle {
80 synchronized(lock) {
81 events.remove(event)
82 }
83 }
84 }
85 }
86
87 /**
88 * Runs the next enqueued task, advancing the virtual time to the time of its scheduled awakening,
89 * unless [condition] holds.
90 */
tryRunNextTaskUnlessnull91 internal fun tryRunNextTaskUnless(condition: () -> Boolean): Boolean {
92 val event = synchronized(lock) {
93 if (condition()) return false
94 val event = events.removeFirstOrNull() ?: return false
95 if (currentTime > event.time)
96 currentTimeAheadOfEvents()
97 currentTime = event.time
98 event
99 }
100 event.dispatcher.processEvent(event.time, event.marker)
101 return true
102 }
103
104 /**
105 * Runs the enqueued tasks in the specified order, advancing the virtual time as needed until there are no more
106 * tasks associated with the dispatchers linked to this scheduler.
107 *
108 * A breaking change from [TestCoroutineDispatcher.advanceTimeBy] is that it no longer returns the total number of
109 * milliseconds by which the execution of this method has advanced the virtual time. If you want to recreate that
110 * functionality, query [currentTime] before and after the execution to achieve the same result.
111 */
112 @ExperimentalCoroutinesApi
<lambda>null113 public fun advanceUntilIdle(): Unit = advanceUntilIdleOr { events.none(TestDispatchEvent<*>::isForeground) }
114
115 /**
116 * [condition]: guaranteed to be invoked under the lock.
117 */
advanceUntilIdleOrnull118 internal fun advanceUntilIdleOr(condition: () -> Boolean) {
119 while (true) {
120 if (!tryRunNextTaskUnless(condition))
121 return
122 }
123 }
124
125 /**
126 * Runs the tasks that are scheduled to execute at this moment of virtual time.
127 */
128 @ExperimentalCoroutinesApi
runCurrentnull129 public fun runCurrent() {
130 val timeMark = synchronized(lock) { currentTime }
131 while (true) {
132 val event = synchronized(lock) {
133 events.removeFirstIf { it.time <= timeMark } ?: return
134 }
135 event.dispatcher.processEvent(event.time, event.marker)
136 }
137 }
138
139 /**
140 * Moves the virtual clock of this dispatcher forward by [the specified amount][delayTimeMillis], running the
141 * scheduled tasks in the meantime.
142 *
143 * Breaking changes from [TestCoroutineDispatcher.advanceTimeBy]:
144 * * Intentionally doesn't return a `Long` value, as its use cases are unclear. We may restore it in the future;
145 * please describe your use cases at [the issue tracker](https://github.com/Kotlin/kotlinx.coroutines/issues/).
146 * For now, it's possible to query [currentTime] before and after execution of this method, to the same effect.
147 * * It doesn't run the tasks that are scheduled at exactly [currentTime] + [delayTimeMillis]. For example,
148 * advancing the time by one millisecond used to run the tasks at the current millisecond *and* the next
149 * millisecond, but now will stop just before executing any task starting at the next millisecond.
150 * * Overflowing the target time used to lead to nothing being done, but will now run the tasks scheduled at up to
151 * (but not including) [Long.MAX_VALUE].
152 *
153 * @throws IllegalStateException if passed a negative [delay][delayTimeMillis].
154 */
155 @ExperimentalCoroutinesApi
advanceTimeBynull156 public fun advanceTimeBy(delayTimeMillis: Long) {
157 require(delayTimeMillis >= 0) { "Can not advance time by a negative delay: $delayTimeMillis" }
158 val startingTime = currentTime
159 val targetTime = addClamping(startingTime, delayTimeMillis)
160 while (true) {
161 val event = synchronized(lock) {
162 val timeMark = currentTime
163 val event = events.removeFirstIf { targetTime > it.time }
164 when {
165 event == null -> {
166 currentTime = targetTime
167 return
168 }
169 timeMark > event.time -> currentTimeAheadOfEvents()
170 else -> {
171 currentTime = event.time
172 event
173 }
174 }
175 }
176 event.dispatcher.processEvent(event.time, event.marker)
177 }
178 }
179
180 /**
181 * Checks that the only tasks remaining in the scheduler are cancelled.
182 */
isIdlenull183 internal fun isIdle(strict: Boolean = true): Boolean =
184 synchronized(lock) {
185 if (strict) events.isEmpty else events.none { !it.isCancelled() }
186 }
187
188 /**
189 * Notifies this scheduler about a dispatch event.
190 *
191 * [context] is the context in which the task will be dispatched.
192 */
sendDispatchEventnull193 internal fun sendDispatchEvent(context: CoroutineContext) {
194 if (context[BackgroundWork] !== BackgroundWork)
195 dispatchEvents.trySend(Unit)
196 }
197
198 /**
199 * Consumes the knowledge that a dispatch event happened recently.
200 */
201 internal val onDispatchEvent: SelectClause1<Unit> get() = dispatchEvents.onReceive
202
203 /**
204 * Returns the [TimeSource] representation of the virtual time of this scheduler.
205 */
206 @ExperimentalCoroutinesApi
207 @ExperimentalTime
208 public val timeSource: TimeSource = object : AbstractLongTimeSource(DurationUnit.MILLISECONDS) {
readnull209 override fun read(): Long = currentTime
210 }
211 }
212
213 // Some error-throwing functions for pretty stack traces
214 private fun currentTimeAheadOfEvents(): Nothing = invalidSchedulerState()
215
216 private fun invalidSchedulerState(): Nothing =
217 throw IllegalStateException("The test scheduler entered an invalid state. Please report this at https://github.com/Kotlin/kotlinx.coroutines/issues.")
218
219 /** [ThreadSafeHeap] node representing a scheduled task, ordered by the planned execution time. */
220 private class TestDispatchEvent<T>(
221 @JvmField val dispatcher: TestDispatcher,
222 private val count: Long,
223 @JvmField val time: Long,
224 @JvmField val marker: T,
225 @JvmField val isForeground: Boolean,
226 // TODO: remove once the deprecated API is gone
227 @JvmField val isCancelled: () -> Boolean
228 ) : Comparable<TestDispatchEvent<*>>, ThreadSafeHeapNode {
229 override var heap: ThreadSafeHeap<*>? = null
230 override var index: Int = 0
231
232 override fun compareTo(other: TestDispatchEvent<*>) =
233 compareValuesBy(this, other, TestDispatchEvent<*>::time, TestDispatchEvent<*>::count)
234
235 override fun toString() = "TestDispatchEvent(time=$time, dispatcher=$dispatcher${if (isForeground) "" else ", background"})"
236 }
237
238 // works with positive `a`, `b`
<lambda>null239 private fun addClamping(a: Long, b: Long): Long = (a + b).let { if (it >= 0) it else Long.MAX_VALUE }
240
checkSchedulerInContextnull241 internal fun checkSchedulerInContext(scheduler: TestCoroutineScheduler, context: CoroutineContext) {
242 context[TestCoroutineScheduler]?.let {
243 check(it === scheduler) {
244 "Detected use of different schedulers. If you need to use several test coroutine dispatchers, " +
245 "create one `TestCoroutineScheduler` and pass it to each of them."
246 }
247 }
248 }
249
250 /**
251 * A coroutine context key denoting that the work is to be executed in the background.
252 * @see [TestScope.backgroundScope]
253 */
254 internal object BackgroundWork : CoroutineContext.Key<BackgroundWork>, CoroutineContext.Element {
255 override val key: CoroutineContext.Key<*>
256 get() = this
257
toStringnull258 override fun toString(): String = "BackgroundWork"
259 }
260
261 private fun<T> ThreadSafeHeap<T>.none(predicate: (T) -> Boolean) where T: ThreadSafeHeapNode, T: Comparable<T> =
262 find(predicate) == null
263