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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 BoundedBufferStorage<Base: AsyncSequence>: Sendable where Base: Sendable {
private let stateMachine: ManagedCriticalState<BoundedBufferStateMachine<Base>>
init(base: Base, limit: Int) {
self.stateMachine = ManagedCriticalState(BoundedBufferStateMachine(base: base, limit: limit))
}
func next() async -> Result<Base.Element, Error>? {
return await withTaskCancellationHandler {
let action: BoundedBufferStateMachine<Base>.NextAction? = self.stateMachine.withCriticalRegion { stateMachine in
let action = stateMachine.next()
switch action {
case .startTask(let base):
self.startTask(stateMachine: &stateMachine, base: base)
return nil
case .suspend:
return action
case .returnResult:
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 .suspend:
break
case .returnResult(let producerContinuation, let result):
producerContinuation?.resume()
return result
case .none:
break
}
return await withUnsafeContinuation { (continuation: UnsafeContinuation<Result<Base.Element, Error>?, Never>) in
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.nextSuspended(continuation: continuation)
}
switch action {
case .none:
break
case .returnResult(let producerContinuation, let result):
producerContinuation?.resume()
continuation.resume(returning: result)
}
}
} onCancel: {
self.interrupted()
}
}
private func startTask(
stateMachine: inout BoundedBufferStateMachine<Base>,
base: Base
) {
let task = Task {
do {
var iterator = base.makeAsyncIterator()
loop: while true {
let shouldSuspend = self.stateMachine.withCriticalRegion { stateMachine -> Bool in
return stateMachine.shouldSuspendProducer()
}
if shouldSuspend {
await withUnsafeContinuation { (continuation: UnsafeContinuation<Void, Never>) in
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.producerSuspended(continuation: continuation)
}
switch action {
case .none:
break
case .resumeProducer:
continuation.resume()
}
}
}
guard let element = try await iterator.next() else {
// the upstream is finished
break loop
}
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.elementProduced(element: element)
}
switch action {
case .none:
break
case .resumeConsumer(let continuation, let result):
continuation.resume(returning: result)
}
}
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.finish(error: nil)
}
switch action {
case .none:
break
case .resumeConsumer(let continuation):
continuation?.resume(returning: nil)
}
} catch {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.finish(error: error)
}
switch action {
case .none:
break
case .resumeConsumer(let continuation):
continuation?.resume(returning: .failure(error))
}
}
}
stateMachine.taskStarted(task: task)
}
func interrupted() {
let action = self.stateMachine.withCriticalRegion { stateMachine in
stateMachine.interrupted()
}
switch action {
case .none:
break
case .resumeProducerAndConsumer(let task, let producerContinuation, let consumerContinuation):
task.cancel()
producerContinuation?.resume()
consumerContinuation?.resume(returning: nil)
}
}
deinit {
self.interrupted()
}
}
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