AsyncChannel.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Async Algorithms open source project
//
// Copyright (c) 2022 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//

/// A channel for sending elements from one task to another with back pressure.
///
/// The `AsyncChannel` class is intended to be used as a communication type between tasks,
/// particularly when one task produces values and another task consumes those values. The back
/// pressure applied by `send(_:)` via the suspension/resume ensures that
/// the production of values does not exceed the consumption of values from iteration. This method
/// suspends after enqueuing the event and is resumed when the next call to `next()`
/// on the `Iterator` is made, or when `finish()` is called from another Task.
/// As `finish()` induces a terminal state, there is no more need for a back pressure management.
/// This function does not suspend and will finish all the pending iterations.
@available(AsyncAlgorithms 1.0,*)
publicfinalclassAsyncChannel<Element:Sendable>:AsyncSequence,Sendable{
publictypealiasElement=Element
publictypealiasAsyncIterator=Iterator

letstorage:ChannelStorage<Element,Never>

publicinit(){
self.storage =ChannelStorage()
}

 /// Sends an element to an awaiting iteration. This function will resume when the next call to `next()` is made
 /// or when a call to `finish()` is made from another task.
 /// If the channel is already finished then this returns immediately.
 /// If the task is cancelled, this function will resume without sending the element.
 /// Other sending operations from other tasks will remain active.
publicfunc send(_ element:Element)async{
awaitself.storage.send(element: element)
}

 /// Immediately resumes all the suspended operations.
 /// All subsequent calls to `next(_:)` will resume immediately.
publicfunc finish(){
self.storage.finish()
}

publicfunc makeAsyncIterator()->Iterator{
Iterator(storage:self.storage)
}

publicstructIterator:AsyncIteratorProtocol{
letstorage:ChannelStorage<Element,Never>

publicmutatingfunc next()async->Element?{
 // Although the storage can throw, its usage in the context of an `AsyncChannel` guarantees it cannot.
 // There is no public way of sending a failure to it.
try!awaitself.storage.next()
}
}
}

@available(*, unavailable)
extensionAsyncChannel.Iterator:Sendable{}