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| 1 | +//===----------------------------------------------------------------------===// |
| 2 | +// |
| 3 | +// This source file is part of the Swift.org open source project |
| 4 | +// |
| 5 | +// Copyright (c) 2025 Apple Inc. and the Swift project authors |
| 6 | +// Licensed under Apache License v2.0 with Runtime Library Exception |
| 7 | +// |
| 8 | +// See https://swift.org/LICENSE.txt for license information |
| 9 | +// |
| 10 | +//===----------------------------------------------------------------------===// |
| 11 | + |
| 12 | +import _Concurrency |
| 13 | + |
| 14 | +@usableFromInline |
| 15 | +@available(SwiftStdlib 5.1, *) |
| 16 | +@_silgen_name("swift_task_addCancellationHandler") |
| 17 | +func _taskAddCancellationHandler(handler: () -> Void) -> UnsafeRawPointer /*CancellationNotificationStatusRecord*/ |
| 18 | + |
| 19 | +@usableFromInline |
| 20 | +@available(SwiftStdlib 5.1, *) |
| 21 | +@_silgen_name("swift_task_removeCancellationHandler") |
| 22 | +func _taskRemoveCancellationHandler( |
| 23 | + record: UnsafeRawPointer /*CancellationNotificationStatusRecord*/ |
| 24 | +) |
| 25 | + |
| 26 | +func withIsolatedTaskCancellationHandler<T: Sendable>( |
| 27 | + operation: @isolated(any) () async throws -> T, |
| 28 | + onCancel handler: @Sendable () -> Void, |
| 29 | + isolation: isolated (any Actor)? = #isolation |
| 30 | +) async rethrows -> T { |
| 31 | + // unconditionally add the cancellation record to the task. |
| 32 | + // if the task was already cancelled, it will be executed right away. |
| 33 | + let record = _taskAddCancellationHandler(handler: handler) |
| 34 | + defer { _taskRemoveCancellationHandler(record: record) } |
| 35 | + |
| 36 | + return try await operation() |
| 37 | +} |
| 38 | + |
| 39 | +/// An asychronous sequence generated from a closure that tracks the transactional changes of `@Observable` types. |
| 40 | +/// |
| 41 | +/// `Observations` conforms to `AsyncSequence`, providing a intutive and safe mechanism to track changes to |
| 42 | +/// types that are marked as `@Observable` by using Swift Concurrency to indicate transactional boundaries |
| 43 | +/// starting from the willSet of the first mutation to the next suspension point of the safe access. |
| 44 | +@available(SwiftStdlib 9999, *) |
| 45 | +public struct Observations<Element: Sendable, Failure: Error>: AsyncSequence, Sendable { |
| 46 | + public enum Iteration: Sendable { |
| 47 | + case next(Element) |
| 48 | + case finish |
| 49 | + } |
| 50 | + |
| 51 | + struct State { |
| 52 | + enum Continuation { |
| 53 | + case cancelled |
| 54 | + case active(UnsafeContinuation<Void, Never>) |
| 55 | + func resume() { |
| 56 | + switch self { |
| 57 | + case .cancelled: break |
| 58 | + case .active(let continuation): continuation.resume() |
| 59 | + } |
| 60 | + } |
| 61 | + } |
| 62 | + var id = 0 |
| 63 | + var continuations: [Int: Continuation] = [:] |
| 64 | + var dirty = false |
| 65 | + |
| 66 | + // create a generation id for the unique identification of the continuations |
| 67 | + // this allows the shared awaiting of the willSets. |
| 68 | + // Most likely, there wont be more than a handful of active iterations |
| 69 | + // so this only needs to be unique for those active iterations |
| 70 | + // that are in the process of calling next. |
| 71 | + static func generation(_ state: _ManagedCriticalState<State>) -> Int { |
| 72 | + state.withCriticalRegion { state in |
| 73 | + defer { state.id &+= 1 } |
| 74 | + return state.id |
| 75 | + } |
| 76 | + } |
| 77 | + |
| 78 | + // the cancellation of awaiting on willSet only ferries in resuming early |
| 79 | + // it is the responsability of the caller to check if the task is actually |
| 80 | + // cancelled after awaiting the willSet to act accordingly. |
| 81 | + static func cancel(_ state: _ManagedCriticalState<State>, id: Int) { |
| 82 | + state.withCriticalRegion { state in |
| 83 | + guard let continuation = state.continuations.removeValue(forKey: id) else { |
| 84 | + // if there was no continuation yet active (e.g. it was cancelled at |
| 85 | + // the start of the invocation, then put a tombstone in to gate that |
| 86 | + // resuming later |
| 87 | + state.continuations[id] = .cancelled |
| 88 | + return nil as Continuation? |
| 89 | + } |
| 90 | + return continuation |
| 91 | + }?.resume() |
| 92 | + } |
| 93 | + |
| 94 | + // fire off ALL awaiting willChange continuations such that they are no |
| 95 | + // longer pending. |
| 96 | + static func emitWillChange(_ state: _ManagedCriticalState<State>) { |
| 97 | + let continuations = state.withCriticalRegion { state in |
| 98 | + // if there are no continuations present then we have to set the state as dirty |
| 99 | + // else if this is uncondiitonally set the state might produce duplicate events |
| 100 | + // one for the dirty and one for the continuation. |
| 101 | + if state.continuations.count == 0 { |
| 102 | + state.dirty = true |
| 103 | + } |
| 104 | + defer { |
| 105 | + state.continuations.removeAll() |
| 106 | + } |
| 107 | + return state.continuations.values |
| 108 | + } |
| 109 | + for continuation in continuations { |
| 110 | + continuation.resume() |
| 111 | + } |
| 112 | + } |
| 113 | + |
| 114 | + // install a willChange continuation into the set of continuations |
| 115 | + // this must take a locally unique id (to the active calls of next) |
| 116 | + static func willChange(isolation iterationIsolation: isolated (any Actor)? = #isolation, state: _ManagedCriticalState<State>, id: Int) async { |
| 117 | + return await withUnsafeContinuation(isolation: iterationIsolation) { continuation in |
| 118 | + state.withCriticalRegion { state in |
| 119 | + defer { state.dirty = false } |
| 120 | + switch state.continuations[id] { |
| 121 | + case .cancelled: |
| 122 | + return continuation as UnsafeContinuation<Void, Never>? |
| 123 | + case .active: |
| 124 | + // the Iterator itself cannot be shared across isolations so any call to next that may share an id is a misbehavior |
| 125 | + // or an internal book-keeping failure |
| 126 | + fatalError("Iterator incorrectly shared across task isolations") |
| 127 | + case .none: |
| 128 | + if state.dirty { |
| 129 | + return continuation |
| 130 | + } else { |
| 131 | + state.continuations[id] = .active(continuation) |
| 132 | + return nil |
| 133 | + } |
| 134 | + } |
| 135 | + }?.resume() |
| 136 | + } |
| 137 | + } |
| 138 | + } |
| 139 | + |
| 140 | + // @isolated(any) closures cannot be composed and retain or forward their isolation |
| 141 | + // this basically would be replaced with `{ .next(elementProducer()) }` if that |
| 142 | + // were to become possible. |
| 143 | + enum Emit { |
| 144 | + case iteration(@isolated(any) @Sendable () throws(Failure) -> Iteration) |
| 145 | + case element(@isolated(any) @Sendable () throws(Failure) -> Element) |
| 146 | + |
| 147 | + var isolation: (any Actor)? { |
| 148 | + switch self { |
| 149 | + case .iteration(let closure): closure.isolation |
| 150 | + case .element(let closure): closure.isolation |
| 151 | + } |
| 152 | + } |
| 153 | + } |
| 154 | + |
| 155 | + let state: _ManagedCriticalState<State> |
| 156 | + let emit: Emit |
| 157 | + |
| 158 | + // internal funnel method for initialziation |
| 159 | + internal init(emit: Emit) { |
| 160 | + self.emit = emit |
| 161 | + self.state = _ManagedCriticalState(State()) |
| 162 | + } |
| 163 | + |
| 164 | + /// Constructs an asynchronous sequence for a given closure by tracking changes of `@Observable` types. |
| 165 | + /// |
| 166 | + /// The emit closure is responsible for extracting a value out of a single or many `@Observable` types. |
| 167 | + /// |
| 168 | + /// - Parameters: |
| 169 | + /// - isolation: The concurrency isolation domain of the caller. |
| 170 | + /// - emit: A closure to generate an element for the sequence. |
| 171 | + public init( |
| 172 | + @_inheritActorContext _ emit: @escaping @isolated(any) @Sendable () throws(Failure) -> Element |
| 173 | + ) { |
| 174 | + self.init(emit: .element(emit)) |
| 175 | + } |
| 176 | + |
| 177 | + /// Constructs an asynchronous sequence for a given closure by tracking changes of `@Observable` types. |
| 178 | + /// |
| 179 | + /// The emit closure is responsible for extracting a value out of a single or many `@Observable` types. This method |
| 180 | + /// continues to be invoked until the .finished option is returned or an error is thrown. |
| 181 | + /// |
| 182 | + /// - Parameters: |
| 183 | + /// - isolation: The concurrency isolation domain of the caller. |
| 184 | + /// - emit: A closure to generate an element for the sequence. |
| 185 | + public static func untilFinished( |
| 186 | + @_inheritActorContext _ emit: @escaping @isolated(any) @Sendable () throws(Failure) -> Iteration |
| 187 | + ) -> Observations<Element, Failure> { |
| 188 | + .init(emit: .iteration(emit)) |
| 189 | + } |
| 190 | + |
| 191 | + public struct Iterator: AsyncIteratorProtocol { |
| 192 | + // the state ivar serves two purposes: |
| 193 | + // 1) to store a critical region of state of the mutations |
| 194 | + // 2) to idenitify the termination of _this_ sequence |
| 195 | + var state: _ManagedCriticalState<State>? |
| 196 | + let emit: Emit |
| 197 | + var started = false |
| 198 | + |
| 199 | + // this is the primary implementation of the tracking |
| 200 | + // it is bound to be called on the specified isolation of the construction |
| 201 | + fileprivate static func trackEmission(isolation trackingIsolation: isolated (any Actor)?, state: _ManagedCriticalState<State>, emit: Emit) throws(Failure) -> Iteration { |
| 202 | + // this ferries in an intermediate form with Result to skip over `withObservationTracking` not handling errors being thrown |
| 203 | + // particularly this case is that the error is also an iteration state transition data point (it terminates the sequence) |
| 204 | + // so we need to hold that to get a chance to catch and clean-up |
| 205 | + let result = withObservationTracking { |
| 206 | + switch emit { |
| 207 | + case .element(let element): |
| 208 | + Result(catching: element).map { Iteration.next($0) } |
| 209 | + case .iteration(let iteration): |
| 210 | + Result(catching: iteration) |
| 211 | + } |
| 212 | + } onChange: { [state] in |
| 213 | + // resume all cases where the awaiting continuations are awaiting a willSet |
| 214 | + State.emitWillChange(state) |
| 215 | + } |
| 216 | + return try result.get() |
| 217 | + } |
| 218 | + |
| 219 | + fileprivate mutating func terminate(throwing failure: Failure? = nil, id: Int) throws(Failure) -> Element? { |
| 220 | + // this is purely defensive to any leaking out of iteration generation ids |
| 221 | + state?.withCriticalRegion { state in |
| 222 | + state.continuations.removeValue(forKey: id) |
| 223 | + }?.resume() |
| 224 | + // flag the sequence as terminal by nil'ing out the state |
| 225 | + state = nil |
| 226 | + if let failure { |
| 227 | + throw failure |
| 228 | + } else { |
| 229 | + return nil |
| 230 | + } |
| 231 | + } |
| 232 | + |
| 233 | + fileprivate mutating func trackEmission(isolation iterationIsolation: isolated (any Actor)?, state: _ManagedCriticalState<State>, id: Int) async throws(Failure) -> Element? { |
| 234 | + guard !Task.isCancelled else { |
| 235 | + // the task was cancelled while awaiting a willChange so ensure a proper termination |
| 236 | + return try terminate(id: id) |
| 237 | + } |
| 238 | + // start by directly tracking the emission via a withObservation tracking on the isolation specified fro mthe init |
| 239 | + switch try await Iterator.trackEmission(isolation: emit.isolation, state: state, emit: emit) { |
| 240 | + case .finish: return try terminate(id: id) |
| 241 | + case .next(let element): return element |
| 242 | + } |
| 243 | + } |
| 244 | + |
| 245 | + public mutating func next(isolation iterationIsolation: isolated (any Actor)? = #isolation) async throws(Failure) -> Element? { |
| 246 | + // early exit if the sequence is terminal already |
| 247 | + guard let state else { return nil } |
| 248 | + // set up an id for this generation |
| 249 | + let id = State.generation(state) |
| 250 | + do { |
| 251 | + // there are two versions; |
| 252 | + // either the tracking has never yet started at all and we need to prime the pump for this specific iterator |
| 253 | + // or the tracking has already started and we are going to await a change |
| 254 | + if !started { |
| 255 | + started = true |
| 256 | + return try await trackEmission(isolation: iterationIsolation, state: state, id: id) |
| 257 | + } else { |
| 258 | + // wait for the willChange (and NOT the value itself) |
| 259 | + // since this is going to be on the isolation of the object (e.g. the isolation specified in the initialization) |
| 260 | + // this will mean our next await for the emission will ensure the suspension return of the willChange context |
| 261 | + // back to the trailing edges of the mutations. In short, this enables the transactionality bounded by the |
| 262 | + // isolation of the mutation. |
| 263 | + await withIsolatedTaskCancellationHandler(operation: { |
| 264 | + await State.willChange(isolation: iterationIsolation, state: state, id: id) |
| 265 | + }, onCancel: { |
| 266 | + // ensure to clean out our continuation uon cancellation |
| 267 | + State.cancel(state, id: id) |
| 268 | + }, isolation: iterationIsolation) |
| 269 | + return try await trackEmission(isolation: iterationIsolation, state: state, id: id) |
| 270 | + } |
| 271 | + } catch { |
| 272 | + // the user threw a failure in the closure so propigate that outwards and terminate the sequence |
| 273 | + return try terminate(throwing: error, id: id) |
| 274 | + } |
| 275 | + } |
| 276 | + } |
| 277 | + |
| 278 | + public func makeAsyncIterator() -> Iterator { |
| 279 | + Iterator(state: state, emit: emit) |
| 280 | + } |
| 281 | +} |
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