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355 lines
12 KiB
Swift
355 lines
12 KiB
Swift
//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2020 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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import Swift
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#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
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@available(SwiftStdlib 5.1, *)
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@_unavailableInEmbedded
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extension Task where Success == Never, Failure == Never {
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@available(*, deprecated, renamed: "Task.sleep(nanoseconds:)")
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/// Suspends the current task for at least the given duration
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/// in nanoseconds.
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///
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/// This function doesn't block the underlying thread.
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public static func sleep(_ duration: UInt64) async {
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return await Builtin.withUnsafeContinuation {
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(continuation: Builtin.RawUnsafeContinuation) -> Void in
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let job = _taskCreateNullaryContinuationJob(
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priority: Int(Task.currentPriority.rawValue),
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continuation: continuation)
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if #available(SwiftStdlibCurrentOS 6.2, *) {
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#if !$Embedded
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if let executor = Task.currentSchedulableExecutor {
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executor.enqueue(ExecutorJob(context: job),
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after: .nanoseconds(duration),
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clock: .continuous)
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return
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}
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#endif
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}
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// If there is no current schedulable executor, fall back to
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// _enqueueJobGlobalWithDelay()
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_enqueueJobGlobalWithDelay(duration, job)
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}
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}
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/// The type of continuation used in the implementation of
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/// sleep(nanoseconds:).
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typealias SleepContinuation = UnsafeContinuation<(), Error>
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/// Describes the state of a sleep() operation.
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@unsafe enum SleepState {
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/// The sleep continuation has not yet begun.
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case notStarted
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// The sleep continuation has been created and is available here.
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case activeContinuation(SleepContinuation)
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/// The sleep has finished.
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case finished
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/// The sleep was canceled.
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case cancelled
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/// The sleep was canceled before it even got started.
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case cancelledBeforeStarted
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/// Decode sleep state from the word of storage.
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init(word: Builtin.Word) {
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switch UInt(word) & 0x03 {
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case 0:
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let continuationBits = UInt(word) & ~0x03
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if continuationBits == 0 {
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unsafe self = unsafe .notStarted
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} else {
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let continuation = unsafe unsafeBitCast(
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continuationBits, to: SleepContinuation.self)
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unsafe self = unsafe .activeContinuation(continuation)
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}
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case 1:
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unsafe self = unsafe .finished
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case 2:
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unsafe self = unsafe .cancelled
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case 3:
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unsafe self = unsafe .cancelledBeforeStarted
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default:
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fatalError("Bitmask failure")
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}
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}
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/// Decode sleep state by loading from the given pointer
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init(loading wordPtr: UnsafeMutablePointer<Builtin.Word>) {
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unsafe self.init(word: Builtin.atomicload_seqcst_Word(wordPtr._rawValue))
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}
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/// Encode sleep state into a word of storage.
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var word: UInt {
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switch unsafe self {
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case .notStarted:
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return 0
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case .activeContinuation(let continuation):
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let continuationBits = unsafe unsafeBitCast(continuation, to: UInt.self)
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return continuationBits
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case .finished:
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return 1
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case .cancelled:
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return 2
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case .cancelledBeforeStarted:
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return 3
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}
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}
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}
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/// A simple wrapper for a pointer to heap allocated storage of a `SleepState`
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/// value. This wrapper is `Sendable` because it facilitates atomic load and
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/// exchange operations on the underlying storage. However, this wrapper is also
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/// _unsafe_ because the owner must manually deallocate the token once it is no
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/// longer needed.
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@unsafe struct UnsafeSleepStateToken: @unchecked Sendable {
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let wordPtr: UnsafeMutablePointer<Builtin.Word>
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/// Allocates the underlying storage and sets the value to `.notStarted`.
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init() {
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unsafe wordPtr = .allocate(capacity: 1)
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unsafe Builtin.atomicstore_seqcst_Word(
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wordPtr._rawValue, SleepState.notStarted.word._builtinWordValue)
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}
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/// Atomically loads the current state.
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func load() -> SleepState {
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return unsafe SleepState(word: Builtin.atomicload_seqcst_Word(wordPtr._rawValue))
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}
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/// Attempts to atomically set the stored value to `desired` if the current
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/// value is equal to `expected`. Returns true if the exchange was successful.
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func exchange(expected: SleepState, desired: SleepState) -> Bool {
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let (_, won) = unsafe Builtin.cmpxchg_seqcst_seqcst_Word(
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wordPtr._rawValue,
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expected.word._builtinWordValue,
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desired.word._builtinWordValue)
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return Bool(_builtinBooleanLiteral: won)
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}
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/// Deallocates the underlying storage.
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func deallocate() {
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unsafe wordPtr.deallocate()
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}
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}
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/// Called when the sleep(nanoseconds:) operation woke up without being
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/// canceled.
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static func onSleepWake(_ token: UnsafeSleepStateToken) {
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while true {
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let state = unsafe token.load()
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switch unsafe state {
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case .notStarted:
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fatalError("Cannot wake before we even started")
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case .activeContinuation(let continuation):
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// We have an active continuation, so try to transition to the
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// "finished" state.
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if unsafe token.exchange(expected: state, desired: .finished) {
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// The sleep finished, so invoke the continuation: we're done.
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unsafe continuation.resume()
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return
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}
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// Try again!
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continue
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case .finished:
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fatalError("Already finished normally, can't do that again")
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case .cancelled:
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// The task was cancelled, which means the continuation was
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// called by the cancellation handler. We need to deallocate the token
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// because it was left over for this task to complete.
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unsafe token.deallocate()
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return
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case .cancelledBeforeStarted:
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// Nothing to do;
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return
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}
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}
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}
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/// Called when the sleep(nanoseconds:) operation has been canceled before
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/// the sleep completed.
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static func onSleepCancel(_ token: UnsafeSleepStateToken) {
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while true {
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let state = unsafe token.load()
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switch unsafe state {
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case .notStarted:
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// We haven't started yet, so try to transition to the cancelled-before
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// started state.
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if unsafe token.exchange(expected: state, desired: .cancelledBeforeStarted) {
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return
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}
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// Try again!
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continue
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case .activeContinuation(let continuation):
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// We have an active continuation, so try to transition to the
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// "cancelled" state.
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if unsafe token.exchange(expected: state, desired: .cancelled) {
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// We recorded the task cancellation before the sleep finished, so
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// invoke the continuation with the cancellation error.
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unsafe continuation.resume(throwing: _Concurrency.CancellationError())
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return
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}
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// Try again!
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continue
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case .finished, .cancelled, .cancelledBeforeStarted:
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// The operation already finished, so there is nothing more to do.
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return
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}
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}
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}
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/// Suspends the current task for at least the given duration
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/// in nanoseconds.
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///
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/// If the task is canceled before the time ends,
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/// this function throws `CancellationError`.
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///
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/// This function doesn't block the underlying thread.
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public static func sleep(nanoseconds duration: UInt64) async throws {
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// Create a token which will initially have the value "not started", which
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// means the continuation has neither been created nor completed.
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let token = unsafe UnsafeSleepStateToken()
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do {
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// Install a cancellation handler to resume the continuation by
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// throwing CancellationError.
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try await withTaskCancellationHandler {
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let _: () = try unsafe await withUnsafeThrowingContinuation { continuation in
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while true {
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let state = unsafe token.load()
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switch unsafe state {
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case .notStarted:
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// Try to swap in the continuation state.
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let newState = unsafe SleepState.activeContinuation(continuation)
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if unsafe !token.exchange(expected: state, desired: newState) {
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// Keep trying!
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continue
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}
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// Create a task that resumes the continuation normally if it
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// finishes first. Enqueue it directly with the delay, so it fires
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// when we're done sleeping.
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let sleepTaskFlags = taskCreateFlags(
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priority: nil, isChildTask: false, copyTaskLocals: false,
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inheritContext: false, enqueueJob: false,
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addPendingGroupTaskUnconditionally: false,
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isDiscardingTask: false, isSynchronousStart: false)
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let (sleepTask, _) = Builtin.createAsyncTask(sleepTaskFlags) {
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unsafe onSleepWake(token)
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}
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let job = Builtin.convertTaskToJob(sleepTask)
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if #available(SwiftStdlibCurrentOS 6.2, *) {
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#if !$Embedded
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if let executor = Task.currentSchedulableExecutor {
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executor.enqueue(ExecutorJob(context: job),
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after: .nanoseconds(duration),
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clock: .continuous)
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return
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}
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#endif
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}
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// If there is no current schedulable executor, fall back to
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// _enqueueJobGlobalWithDelay()
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_enqueueJobGlobalWithDelay(duration, job)
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return
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case .activeContinuation, .finished:
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fatalError("Impossible to have multiple active continuations")
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case .cancelled:
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fatalError("Impossible to have cancelled before we began")
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case .cancelledBeforeStarted:
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// Finish the continuation normally. We'll throw later, after
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// we clean up.
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unsafe continuation.resume()
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return
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}
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}
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}
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} onCancel: {
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unsafe onSleepCancel(token)
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}
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// Determine whether we got cancelled before we even started.
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let cancelledBeforeStarted: Bool
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switch unsafe token.load() {
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case .notStarted, .activeContinuation, .cancelled:
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fatalError("Invalid state for non-cancelled sleep task")
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case .cancelledBeforeStarted:
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cancelledBeforeStarted = true
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case .finished:
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cancelledBeforeStarted = false
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}
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// We got here without being cancelled, so deallocate the storage for
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// the flag word and continuation.
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unsafe token.deallocate()
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// If we got cancelled before we even started, through the cancellation
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// error now.
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if cancelledBeforeStarted {
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throw _Concurrency.CancellationError()
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}
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} catch {
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// The task was cancelled; propagate the error. The "on wake" task is
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// responsible for deallocating the flag word and continuation, if it's
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// still running.
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throw error
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}
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}
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}
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#else
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@available(SwiftStdlib 5.1, *)
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@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
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extension Task where Success == Never, Failure == Never {
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@available(SwiftStdlib 5.1, *)
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@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
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public static func sleep(_ duration: UInt64) async {
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fatalError("Unavailable in task-to-thread concurrency model")
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}
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@available(SwiftStdlib 5.1, *)
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@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
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public static func sleep(nanoseconds duration: UInt64) async throws {
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fatalError("Unavailable in task-to-thread concurrency model")
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}
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}
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#endif
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