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| 1 | +/* |
| 2 | + * Copyright 2016-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license. |
| 3 | + */ |
| 4 | + |
| 5 | +package kotlinx.coroutines.flow.internal |
| 6 | + |
| 7 | +import kotlinx.coroutines.* |
| 8 | +import kotlinx.coroutines.flow.* |
| 9 | +import kotlinx.coroutines.internal.ScopeCoroutine |
| 10 | +import kotlin.coroutines.* |
| 11 | +import kotlin.jvm.* |
| 12 | + |
| 13 | +internal expect class SafeCollector<T>( |
| 14 | + collector: FlowCollector<T>, |
| 15 | + collectContext: CoroutineContext |
| 16 | +) : FlowCollector<T> { |
| 17 | + internal val collector: FlowCollector<T> |
| 18 | + internal val collectContext: CoroutineContext |
| 19 | + internal val collectContextSize: Int |
| 20 | + public fun releaseIntercepted() |
| 21 | +} |
| 22 | + |
| 23 | +@JvmName("checkContext") // For prettier stack traces |
| 24 | +internal fun SafeCollector<*>.checkContext(currentContext: CoroutineContext) { |
| 25 | + val result = currentContext.fold(0) fold@{ count, element -> |
| 26 | + val key = element.key |
| 27 | + val collectElement = collectContext[key] |
| 28 | + if (key !== Job) { |
| 29 | + return@fold if (element !== collectElement) Int.MIN_VALUE |
| 30 | + else count + 1 |
| 31 | + } |
| 32 | + |
| 33 | + val collectJob = collectElement as Job? |
| 34 | + val emissionParentJob = (element as Job).transitiveCoroutineParent(collectJob) |
| 35 | + /* |
| 36 | + * Code like |
| 37 | + * ``` |
| 38 | + * coroutineScope { |
| 39 | + * launch { |
| 40 | + * emit(1) |
| 41 | + * } |
| 42 | + * |
| 43 | + * launch { |
| 44 | + * emit(2) |
| 45 | + * } |
| 46 | + * } |
| 47 | + * ``` |
| 48 | + * is prohibited because 'emit' is not thread-safe by default. Use 'channelFlow' instead if you need concurrent emission |
| 49 | + * or want to switch context dynamically (e.g. with `withContext`). |
| 50 | + * |
| 51 | + * Note that collecting from another coroutine is allowed, e.g.: |
| 52 | + * ``` |
| 53 | + * coroutineScope { |
| 54 | + * val channel = produce { |
| 55 | + * collect { value -> |
| 56 | + * send(value) |
| 57 | + * } |
| 58 | + * } |
| 59 | + * channel.consumeEach { value -> |
| 60 | + * emit(value) |
| 61 | + * } |
| 62 | + * } |
| 63 | + * ``` |
| 64 | + * is a completely valid. |
| 65 | + */ |
| 66 | + if (emissionParentJob !== collectJob) { |
| 67 | + error( |
| 68 | + "Flow invariant is violated:\n" + |
| 69 | + "\t\tEmission from another coroutine is detected.\n" + |
| 70 | + "\t\tChild of $emissionParentJob, expected child of $collectJob.\n" + |
| 71 | + "\t\tFlowCollector is not thread-safe and concurrent emissions are prohibited.\n" + |
| 72 | + "\t\tTo mitigate this restriction please use 'channelFlow' builder instead of 'flow'" |
| 73 | + ) |
| 74 | + } |
| 75 | + |
| 76 | + /* |
| 77 | + * If collect job is null (-> EmptyCoroutineContext, probably run from `suspend fun main`), then invariant is maintained |
| 78 | + * (common transitive parent is "null"), but count check will fail, so just do not count job context element when |
| 79 | + * flow is collected from EmptyCoroutineContext |
| 80 | + */ |
| 81 | + if (collectJob == null) count else count + 1 |
| 82 | + } |
| 83 | + if (result != collectContextSize) { |
| 84 | + error( |
| 85 | + "Flow invariant is violated:\n" + |
| 86 | + "\t\tFlow was collected in $collectContext,\n" + |
| 87 | + "\t\tbut emission happened in $currentContext.\n" + |
| 88 | + "\t\tPlease refer to 'flow' documentation or use 'flowOn' instead" |
| 89 | + ) |
| 90 | + } |
| 91 | +} |
| 92 | + |
| 93 | +internal tailrec fun Job?.transitiveCoroutineParent(collectJob: Job?): Job? { |
| 94 | + if (this === null) return null |
| 95 | + if (this === collectJob) return this |
| 96 | + if (this !is ScopeCoroutine<*>) return this |
| 97 | + return parent.transitiveCoroutineParent(collectJob) |
| 98 | +} |
| 99 | + |
| 100 | +/** |
| 101 | + * An analogue of the [flow] builder that does not check the context of execution of the resulting flow. |
| 102 | + * Used in our own operators where we trust the context of invocations. |
| 103 | + */ |
| 104 | +@PublishedApi |
| 105 | +internal inline fun <T> unsafeFlow(@BuilderInference crossinline block: suspend FlowCollector<T>.() -> Unit): Flow<T> { |
| 106 | + return object : Flow<T> { |
| 107 | + override suspend fun collect(collector: FlowCollector<T>) { |
| 108 | + collector.block() |
| 109 | + } |
| 110 | + } |
| 111 | +} |
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