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//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
final class ZipStorage<Base1: AsyncSequence, Base2: AsyncSequence, Base3: AsyncSequence>: Sendable
where Base1: Sendable, Base1.Element: Sendable, Base2: Sendable, Base2.Element: Sendable, Base3: Sendable, Base3.Element: Sendable {
typealias StateMachine = ZipStateMachine<Base1, Base2, Base3>
private let stateMachine: ManagedCriticalState<StateMachine>
init(_ base1: Base1, _ base2: Base2, _ base3: Base3?) {
self.stateMachine = .init(.init(base1: base1, base2: base2, base3: base3))
}
func iteratorDeinitialized() {
let action = self.stateMachine.withCriticalRegion { $0.iteratorDeinitialized() }
switch action {
case .cancelTaskAndUpstreamContinuations(
let task,
let upstreamContinuation
):
upstreamContinuation.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
case .none:
break
}
}
func next() async rethrows -> (Base1.Element, Base2.Element, Base3.Element?)? {
try await withTaskCancellationHandler {
let result = await withUnsafeContinuation { continuation in
let action: StateMachine.NextAction? = self.stateMachine.withCriticalRegion { stateMachine in
let action = stateMachine.next(for: continuation)
switch action {
case .startTask(let base1, let base2, let base3):
// first iteration, we start one child task per base to iterate over them
self.startTask(
stateMachine: &stateMachine,
base1: base1,
base2: base2,
base3: base3,
downstreamContinuation: continuation
)
return nil
case .resumeUpstreamContinuations:
return action
case .resumeDownstreamContinuationWithNil:
return action
}
}
switch action {
case .startTask:
// We are handling the startTask in the lock already because we want to avoid
// other inputs interleaving while starting the task
fatalError("Internal inconsistency")
case .resumeUpstreamContinuations(let upstreamContinuations):
// bases can be iterated over for 1 iteration so their next value can be retrieved
upstreamContinuations.forEach { $0.resume() }
case .resumeDownstreamContinuationWithNil(let continuation):
// the async sequence is already finished, immediately resuming
continuation.resume(returning: .success(nil))
case .none:
break
}
}
return try result._rethrowGet()
} onCancel: {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.cancelled()
}
switch action {
case .resumeDownstreamContinuationWithNilAndCancelTaskAndUpstreamContinuations(
let downstreamContinuation,
let task,
let upstreamContinuations
):
upstreamContinuations.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
downstreamContinuation.resume(returning: .success(nil))
case .cancelTaskAndUpstreamContinuations(let task, let upstreamContinuations):
upstreamContinuations.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
case .none:
break
}
}
}
private func startTask(
stateMachine: inout StateMachine,
base1: Base1,
base2: Base2,
base3: Base3?,
downstreamContinuation: StateMachine.DownstreamContinuation
) {
// This creates a new `Task` that is iterating the upstream
// sequences. We must store it to cancel it at the right times.
let task = Task {
await withThrowingTaskGroup(of: Void.self) { group in
// For each upstream sequence we are adding a child task that
// is consuming the upstream sequence
group.addTask {
var base1Iterator = base1.makeAsyncIterator()
while true {
// We are creating a continuation before requesting the next
// element from upstream. This continuation is only resumed
// if the downstream consumer called `next` to signal his demand.
try await withUnsafeThrowingContinuation { continuation in
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.childTaskSuspended(baseIndex: 0, continuation: continuation)
}
switch action {
case .resumeContinuation(let upstreamContinuation):
upstreamContinuation.resume()
case .resumeContinuationWithError(let upstreamContinuation, let error):
upstreamContinuation.resume(throwing: error)
case .none:
break
}
}
if let element1 = try await base1Iterator.next() {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.elementProduced((element1, nil, nil))
}
switch action {
case .resumeContinuation(let downstreamContinuation, let result):
downstreamContinuation.resume(returning: result)
case .none:
break
}
} else {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.upstreamFinished()
}
switch action {
case .resumeContinuationWithNilAndCancelTaskAndUpstreamContinuations(
let downstreamContinuation,
let task,
let upstreamContinuations
):
upstreamContinuations.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
downstreamContinuation.resume(returning: .success(nil))
case .none:
break
}
}
}
}
group.addTask {
var base2Iterator = base2.makeAsyncIterator()
while true {
// We are creating a continuation before requesting the next
// element from upstream. This continuation is only resumed
// if the downstream consumer called `next` to signal his demand.
try await withUnsafeThrowingContinuation { continuation in
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.childTaskSuspended(baseIndex: 1, continuation: continuation)
}
switch action {
case .resumeContinuation(let upstreamContinuation):
upstreamContinuation.resume()
case .resumeContinuationWithError(let upstreamContinuation, let error):
upstreamContinuation.resume(throwing: error)
case .none:
break
}
}
if let element2 = try await base2Iterator.next() {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.elementProduced((nil, element2, nil))
}
switch action {
case .resumeContinuation(let downstreamContinuation, let result):
downstreamContinuation.resume(returning: result)
case .none:
break
}
} else {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.upstreamFinished()
}
switch action {
case .resumeContinuationWithNilAndCancelTaskAndUpstreamContinuations(
let downstreamContinuation,
let task,
let upstreamContinuations
):
upstreamContinuations.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
downstreamContinuation.resume(returning: .success(nil))
case .none:
break
}
}
}
}
if let base3 = base3 {
group.addTask {
var base3Iterator = base3.makeAsyncIterator()
while true {
// We are creating a continuation before requesting the next
// element from upstream. This continuation is only resumed
// if the downstream consumer called `next` to signal his demand.
try await withUnsafeThrowingContinuation { continuation in
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.childTaskSuspended(baseIndex: 2, continuation: continuation)
}
switch action {
case .resumeContinuation(let upstreamContinuation):
upstreamContinuation.resume()
case .resumeContinuationWithError(let upstreamContinuation, let error):
upstreamContinuation.resume(throwing: error)
case .none:
break
}
}
if let element3 = try await base3Iterator.next() {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.elementProduced((nil, nil, element3))
}
switch action {
case .resumeContinuation(let downstreamContinuation, let result):
downstreamContinuation.resume(returning: result)
case .none:
break
}
} else {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.upstreamFinished()
}
switch action {
case .resumeContinuationWithNilAndCancelTaskAndUpstreamContinuations(
let downstreamContinuation,
let task,
let upstreamContinuations
):
upstreamContinuations.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
downstreamContinuation.resume(returning: .success(nil))
case .none:
break
}
}
}
}
}
while !group.isEmpty {
do {
try await group.next()
} catch {
// One of the upstream sequences threw an error
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.upstreamThrew(error)
}
switch action {
case .resumeContinuationWithErrorAndCancelTaskAndUpstreamContinuations(
let downstreamContinuation,
let error,
let task,
let upstreamContinuations
):
upstreamContinuations.forEach { $0.resume(throwing: CancellationError()) }
task.cancel()
downstreamContinuation.resume(returning: .failure(error))
case .none:
break
}
group.cancelAll()
}
}
}
}
stateMachine.taskIsStarted(task: task, downstreamContinuation: downstreamContinuation)
}
}
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