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Coroutines support libraries for Kotlin
/*
* Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
*/
package kotlinx.coroutines
import kotlinx.atomicfu.*
import kotlin.coroutines.*
/**
* Awaits for completion of given deferred values without blocking a thread and resumes normally with the list of values
* when all deferred computations are complete or resumes with the first thrown exception if any of computations
* complete exceptionally including cancellation.
*
* This function is **not** equivalent to `deferreds.map { it.await() }` which fails only when it sequentially
* gets to wait for the failing deferred, while this `awaitAll` fails immediately as soon as any of the deferreds fail.
*
* This suspending function is cancellable.
* If the [Job] of the current coroutine is cancelled or completed while this suspending function is waiting,
* this function immediately resumes with [CancellationException].
* There is a **prompt cancellation guarantee**. If the job was cancelled while this function was
* suspended, it will not resume successfully. See [suspendCancellableCoroutine] documentation for low-level details.
*/
public suspend fun awaitAll(vararg deferreds: Deferred): List =
if (deferreds.isEmpty()) emptyList() else AwaitAll(deferreds).await()
/**
* Awaits for completion of given deferred values without blocking a thread and resumes normally with the list of values
* when all deferred computations are complete or resumes with the first thrown exception if any of computations
* complete exceptionally including cancellation.
*
* This function is **not** equivalent to `this.map { it.await() }` which fails only when when it sequentially
* gets to wait the failing deferred, while this `awaitAll` fails immediately as soon as any of the deferreds fail.
*
* This suspending function is cancellable.
* If the [Job] of the current coroutine is cancelled or completed while this suspending function is waiting,
* this function immediately resumes with [CancellationException].
* There is a **prompt cancellation guarantee**. If the job was cancelled while this function was
* suspended, it will not resume successfully. See [suspendCancellableCoroutine] documentation for low-level details.
*/
public suspend fun Collection>.awaitAll(): List =
if (isEmpty()) emptyList() else AwaitAll(toTypedArray()).await()
/**
* Suspends current coroutine until all given jobs are complete.
* This method is semantically equivalent to joining all given jobs one by one with `jobs.forEach { it.join() }`.
*
* This suspending function is cancellable.
* If the [Job] of the current coroutine is cancelled or completed while this suspending function is waiting,
* this function immediately resumes with [CancellationException].
* There is a **prompt cancellation guarantee**. If the job was cancelled while this function was
* suspended, it will not resume successfully. See [suspendCancellableCoroutine] documentation for low-level details.
*/
public suspend fun joinAll(vararg jobs: Job): Unit = jobs.forEach { it.join() }
/**
* Suspends current coroutine until all given jobs are complete.
* This method is semantically equivalent to joining all given jobs one by one with `forEach { it.join() }`.
*
* This suspending function is cancellable.
* If the [Job] of the current coroutine is cancelled or completed while this suspending function is waiting,
* this function immediately resumes with [CancellationException].
* There is a **prompt cancellation guarantee**. If the job was cancelled while this function was
* suspended, it will not resume successfully. See [suspendCancellableCoroutine] documentation for low-level details.
*/
public suspend fun Collection.joinAll(): Unit = forEach { it.join() }
private class AwaitAll(private val deferreds: Array>) {
private val notCompletedCount = atomic(deferreds.size)
suspend fun await(): List = suspendCancellableCoroutine { cont ->
// Intricate dance here
// Step 1: Create nodes and install them as completion handlers, they may fire!
val nodes = Array(deferreds.size) { i ->
val deferred = deferreds[i]
deferred.start() // To properly await lazily started deferreds
AwaitAllNode(cont).apply {
setHandle(deferred.invokeOnCompletion(asHandler))
}
}
val disposer = DisposeHandlersOnCancel(nodes)
// Step 2: Set disposer to each node
nodes.forEach { it.setDisposer(disposer) }
// Here we know that if any code the nodes complete, it will dispose the rest
// Step 3: Now we can check if continuation is complete
if (cont.isCompleted) {
// it is already complete while handlers were being installed -- dispose them all
disposer.disposeAll()
} else {
cont.invokeOnCancellation(handler = disposer.asHandler)
}
}
private inner class DisposeHandlersOnCancel(private val nodes: Array) : CancelHandler() {
fun disposeAll() {
nodes.forEach { it.disposeHandle() }
}
override fun invoke(cause: Throwable?) { disposeAll() }
override fun toString(): String = "DisposeHandlersOnCancel[$nodes]"
}
private inner class AwaitAllNode(private val continuation: CancellableContinuation>) : JobNode() {
private val _handle = atomic(null)
private val _disposer = atomic(null)
fun setHandle(handle: DisposableHandle) { _handle.value = handle }
fun setDisposer(disposer: DisposeHandlersOnCancel) { _disposer.value = disposer }
fun disposeHandle() {
_handle.value?.dispose()
_handle.value = null
}
override fun invoke(cause: Throwable?) {
if (cause != null) {
val token = continuation.tryResumeWithException(cause)
if (token != null) {
continuation.completeResume(token)
// volatile read of disposer AFTER continuation is complete
// and if disposer was already set (all handlers where already installed, then dispose them all)
_disposer.value?.disposeAll()
}
} else if (notCompletedCount.decrementAndGet() == 0) {
continuation.resume(deferreds.map { it.getCompleted() })
// Note that all deferreds are complete here, so we don't need to dispose their nodes
}
// Release all the refs for Kotlin/Native
_handle.value = null
_disposer.value = null
}
}
}