1 /*
<lambda>null2 * Copyright 2016-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
3 */
4 @file:OptIn(ExperimentalContracts::class)
5
6 package kotlinx.coroutines
7
8 import kotlinx.coroutines.internal.*
9 import kotlinx.coroutines.intrinsics.*
10 import kotlin.contracts.*
11 import kotlin.coroutines.*
12 import kotlin.coroutines.intrinsics.*
13
14 /**
15 * Defines a scope for new coroutines. Every **coroutine builder** (like [launch], [async], etc)
16 * is an extension on [CoroutineScope] and inherits its [coroutineContext][CoroutineScope.coroutineContext]
17 * to automatically propagate all its elements and cancellation.
18 *
19 * The best ways to obtain a standalone instance of the scope are [CoroutineScope()] and [MainScope()] factory functions.
20 * Additional context elements can be appended to the scope using the [plus][CoroutineScope.plus] operator.
21 *
22 * ### Convention for structured concurrency
23 *
24 * Manual implementation of this interface is not recommended, implementation by delegation should be preferred instead.
25 * By convention, the [context of a scope][CoroutineScope.coroutineContext] should contain an instance of a
26 * [job][Job] to enforce the discipline of **structured concurrency** with propagation of cancellation.
27 *
28 * Every coroutine builder (like [launch], [async], etc)
29 * and every scoping function (like [coroutineScope], [withContext], etc) provides _its own_ scope
30 * with its own [Job] instance into the inner block of code it runs.
31 * By convention, they all wait for all the coroutines inside their block to complete before completing themselves,
32 * thus enforcing the structured concurrency. See [Job] documentation for more details.
33 *
34 * ### Android usage
35 *
36 * Android has first-party support for coroutine scope in all entities with the lifecycle.
37 * See [the corresponding documentation](https://developer.android.com/topic/libraries/architecture/coroutines#lifecyclescope).
38 *
39 * ### Custom usage
40 *
41 * [CoroutineScope] should be implemented or declared as a property on entities with a well-defined lifecycle that are
42 * responsible for launching children coroutines, for example:
43 *
44 * ```
45 * class MyUIClass {
46 * val scope = MainScope() // the scope of MyUIClass
47 *
48 * fun destroy() { // destroys an instance of MyUIClass
49 * scope.cancel() // cancels all coroutines launched in this scope
50 * // ... do the rest of cleanup here ...
51 * }
52 *
53 * /*
54 * * Note: if this instance is destroyed or any of the launched coroutines
55 * * in this method throws an exception, then all nested coroutines are cancelled.
56 * */
57 * fun showSomeData() = scope.launch { // launched in the main thread
58 * // ... here we can use suspending functions or coroutine builders with other dispatchers
59 * draw(data) // draw in the main thread
60 * }
61 * }
62 * ```
63 */
64 public interface CoroutineScope {
65 /**
66 * The context of this scope.
67 * Context is encapsulated by the scope and used for implementation of coroutine builders that are extensions on the scope.
68 * Accessing this property in general code is not recommended for any purposes except accessing the [Job] instance for advanced usages.
69 *
70 * By convention, should contain an instance of a [job][Job] to enforce structured concurrency.
71 */
72 public val coroutineContext: CoroutineContext
73 }
74
75 /**
76 * Adds the specified coroutine context to this scope, overriding existing elements in the current
77 * scope's context with the corresponding keys.
78 *
79 * This is a shorthand for `CoroutineScope(thisScope + context)`.
80 */
plusnull81 public operator fun CoroutineScope.plus(context: CoroutineContext): CoroutineScope =
82 ContextScope(coroutineContext + context)
83
84 /**
85 * Creates the main [CoroutineScope] for UI components.
86 *
87 * Example of use:
88 * ```
89 * class MyAndroidActivity {
90 * private val scope = MainScope()
91 *
92 * override fun onDestroy() {
93 * super.onDestroy()
94 * scope.cancel()
95 * }
96 * }
97 * ```
98 *
99 * The resulting scope has [SupervisorJob] and [Dispatchers.Main] context elements.
100 * If you want to append additional elements to the main scope, use [CoroutineScope.plus] operator:
101 * `val scope = MainScope() + CoroutineName("MyActivity")`.
102 */
103 @Suppress("FunctionName")
104 public fun MainScope(): CoroutineScope = ContextScope(SupervisorJob() + Dispatchers.Main)
105
106 /**
107 * Returns `true` when the current [Job] is still active (has not completed and was not cancelled yet).
108 *
109 * Check this property in long-running computation loops to support cancellation:
110 * ```
111 * while (isActive) {
112 * // do some computation
113 * }
114 * ```
115 *
116 * This property is a shortcut for `coroutineContext.isActive` in the scope when
117 * [CoroutineScope] is available.
118 * See [coroutineContext][kotlin.coroutines.coroutineContext],
119 * [isActive][kotlinx.coroutines.isActive] and [Job.isActive].
120 */
121 @Suppress("EXTENSION_SHADOWED_BY_MEMBER")
122 public val CoroutineScope.isActive: Boolean
123 get() = coroutineContext[Job]?.isActive ?: true
124
125 /**
126 * A global [CoroutineScope] not bound to any job.
127 *
128 * Global scope is used to launch top-level coroutines which are operating on the whole application lifetime
129 * and are not cancelled prematurely.
130 * Another use of the global scope is operators running in [Dispatchers.Unconfined], which don't have any job associated with them.
131 *
132 * Application code usually should use an application-defined [CoroutineScope]. Using
133 * [async][CoroutineScope.async] or [launch][CoroutineScope.launch]
134 * on the instance of [GlobalScope] is highly discouraged.
135 *
136 * Usage of this interface may look like this:
137 *
138 * ```
139 * fun ReceiveChannel<Int>.sqrt(): ReceiveChannel<Double> = GlobalScope.produce(Dispatchers.Unconfined) {
140 * for (number in this) {
141 * send(Math.sqrt(number))
142 * }
143 * }
144 * ```
145 */
146 public object GlobalScope : CoroutineScope {
147 /**
148 * Returns [EmptyCoroutineContext].
149 */
150 override val coroutineContext: CoroutineContext
151 get() = EmptyCoroutineContext
152 }
153
154 /**
155 * Creates a [CoroutineScope] and calls the specified suspend block with this scope.
156 * The provided scope inherits its [coroutineContext][CoroutineScope.coroutineContext] from the outer scope, but overrides
157 * the context's [Job].
158 *
159 * This function is designed for _parallel decomposition_ of work. When any child coroutine in this scope fails,
160 * this scope fails and all the rest of the children are cancelled (for a different behavior see [supervisorScope]).
161 * This function returns as soon as the given block and all its children coroutines are completed.
162 * A usage example of a scope looks like this:
163 *
164 * ```
165 * suspend fun showSomeData() = coroutineScope {
166 * val data = async(Dispatchers.IO) { // <- extension on current scope
167 * ... load some UI data for the Main thread ...
168 * }
169 *
170 * withContext(Dispatchers.Main) {
171 * doSomeWork()
172 * val result = data.await()
173 * display(result)
174 * }
175 * }
176 * ```
177 *
178 * The scope in this example has the following semantics:
179 * 1) `showSomeData` returns as soon as the data is loaded and displayed in the UI.
180 * 2) If `doSomeWork` throws an exception, then the `async` task is cancelled and `showSomeData` rethrows that exception.
181 * 3) If the outer scope of `showSomeData` is cancelled, both started `async` and `withContext` blocks are cancelled.
182 * 4) If the `async` block fails, `withContext` will be cancelled.
183 *
184 * The method may throw a [CancellationException] if the current job was cancelled externally
185 * or may throw a corresponding unhandled [Throwable] if there is any unhandled exception in this scope
186 * (for example, from a crashed coroutine that was started with [launch][CoroutineScope.launch] in this scope).
187 */
coroutineScopenull188 public suspend fun <R> coroutineScope(block: suspend CoroutineScope.() -> R): R {
189 contract {
190 callsInPlace(block, InvocationKind.EXACTLY_ONCE)
191 }
192 return suspendCoroutineUninterceptedOrReturn { uCont ->
193 val coroutine = ScopeCoroutine(uCont.context, uCont)
194 coroutine.startUndispatchedOrReturn(coroutine, block)
195 }
196 }
197
198 /**
199 * Creates a [CoroutineScope] that wraps the given coroutine [context].
200 *
201 * If the given [context] does not contain a [Job] element, then a default `Job()` is created.
202 * This way, cancellation or failure of any child coroutine in this scope cancels all the other children,
203 * just like inside [coroutineScope] block.
204 */
205 @Suppress("FunctionName")
CoroutineScopenull206 public fun CoroutineScope(context: CoroutineContext): CoroutineScope =
207 ContextScope(if (context[Job] != null) context else context + Job())
208
209 /**
210 * Cancels this scope, including its job and all its children with an optional cancellation [cause].
211 * A cause can be used to specify an error message or to provide other details on
212 * a cancellation reason for debugging purposes.
213 * Throws [IllegalStateException] if the scope does not have a job in it.
214 */
215 public fun CoroutineScope.cancel(cause: CancellationException? = null) {
216 val job = coroutineContext[Job] ?: error("Scope cannot be cancelled because it does not have a job: $this")
217 job.cancel(cause)
218 }
219
220 /**
221 * Cancels this scope, including its job and all its children with a specified diagnostic error [message].
222 * A [cause] can be specified to provide additional details on a cancellation reason for debugging purposes.
223 * Throws [IllegalStateException] if the scope does not have a job in it.
224 */
cancelnull225 public fun CoroutineScope.cancel(message: String, cause: Throwable? = null): Unit = cancel(CancellationException(message, cause))
226
227 /**
228 * Ensures that current scope is [active][CoroutineScope.isActive].
229 *
230 * If the job is no longer active, throws [CancellationException].
231 * If the job was cancelled, thrown exception contains the original cancellation cause.
232 * This function does not do anything if there is no [Job] in the scope's [coroutineContext][CoroutineScope.coroutineContext].
233 *
234 * This method is a drop-in replacement for the following code, but with more precise exception:
235 * ```
236 * if (!isActive) {
237 * throw CancellationException()
238 * }
239 * ```
240 *
241 * @see CoroutineContext.ensureActive
242 */
243 public fun CoroutineScope.ensureActive(): Unit = coroutineContext.ensureActive()
244
245
246 /**
247 * Returns the current [CoroutineContext] retrieved by using [kotlin.coroutines.coroutineContext].
248 * This function is an alias to avoid name clash with [CoroutineScope.coroutineContext] in a receiver position:
249 *
250 * ```
251 * launch { // this: CoroutineScope
252 * val flow = flow<Unit> {
253 * coroutineContext // Resolves into the context of outer launch, which is incorrect, see KT-38033
254 * currentCoroutineContext() // Retrieves actual context where the flow is collected
255 * }
256 * }
257 * ```
258 */
259 public suspend inline fun currentCoroutineContext(): CoroutineContext = coroutineContext
260