1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394
|
//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2020-2021 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
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import Swift
@_implementationOnly import _SwiftConcurrencyShims
// Macros are disabled when Swift is built without swift-syntax.
#if $Macros && hasAttribute(attached)
/// Macro that introduces a ``TaskLocal-class`` binding.
///
/// For information about task-local bindings, see ``TaskLocal-class``.
///
/// - SeeAlso: ``TaskLocal-class``
@available(SwiftStdlib 5.1, *)
@attached(accessor)
@attached(peer, names: prefixed(`$`))
public macro TaskLocal() =
#externalMacro(module: "SwiftMacros", type: "TaskLocalMacro")
#endif
/// Wrapper type that defines a task-local value key.
///
/// A task-local value is a value that can be bound and read in the context of a
/// ``Task``. It is implicitly carried with the task, and is accessible by any
/// child tasks it creates (such as TaskGroup or `async let` created tasks).
///
/// ### Task-local declarations
///
/// Task locals must be declared as static properties or global properties, like this:
///
/// enum Example {
/// @TaskLocal
/// static let traceID: TraceID?
/// }
///
/// // Global task local properties are supported since Swift 6.0:
/// @TaskLocal
/// var contextualNumber: Int = 12
///
/// ### Default values
/// Reading a task local value when no value was bound to it results in returning
/// its default value. For a task local declared as optional (such as e.g. `TraceID?`),
/// this defaults to nil, however a different default value may be defined at declaration
/// site of the task local, like this:
///
/// enum Example {
/// @TaskLocal
/// static let traceID: TraceID = TraceID.default
/// }
///
/// The default value is returned whenever the task-local is read
/// from a context which either: has no task available to read the value from
/// (e.g. a synchronous function, called without any asynchronous function in its call stack),
/// or no value was bound within the scope of the current task or any of its parent tasks.
///
/// ### Reading task-local values
/// Reading task local values is simple and looks the same as-if reading a normal
/// static property:
///
/// guard let traceID = Example.traceID else {
/// print("no trace id")
/// return
/// }
/// print(traceID)
///
/// It is possible to perform task-local value reads from either asynchronous
/// or synchronous functions.
///
/// ### Binding task-local values
/// Task local values cannot be `set` directly and must instead be bound using
/// the scoped `$traceID.withValue() { ... }` operation. The value is only bound
/// for the duration of that scope, and is available to any child tasks which
/// are created within that scope.
///
/// Detached tasks do not inherit task-local values, however tasks created using
/// the `Task { ... }` initializer do inherit task-locals by copying them to the
/// new asynchronous task, even though it is an un-structured task.
///
/// ### Using task local values outside of tasks
/// It is possible to bind and read task local values outside of tasks.
///
/// This comes in handy within synchronous functions which are not guaranteed
/// to be called from within a task. When binding a task-local value from
/// outside of a task, the runtime will set a thread-local in which the same
/// storage mechanism as used within tasks will be used. This means that you
/// can reliably bind and read task local values without having to worry
/// about the specific calling context, e.g.:
///
/// func enter() {
/// Example.$traceID.withValue("1234") {
/// read() // always "1234", regardless if enter() was called from inside a task or not:
/// }
///
/// func read() -> String {
/// if let value = Self.traceID {
/// "\(value)"
/// } else {
/// "<no value>"
/// }
/// }
///
/// // 1) Call `enter` from non-Task code
/// // e.g. synchronous main() or non-Task thread (e.g. a plain pthread)
/// enter()
///
/// // 2) Call 'enter' from Task
/// Task {
/// enter()
/// }
///
/// In either cases listed above, the binding and reading of the task-local value works as expected.
///
/// ### Examples
///
///
/// enum Example {
/// @TaskLocal
/// static var traceID: TraceID?
/// }
///
/// func read() -> String {
/// if let value = Self.traceID {
/// "\(value)"
/// } else {
/// "<no value>"
/// }
/// }
///
/// await Example.$traceID.withValue(1234) { // bind the value
/// print("traceID: \(Example.traceID)") // traceID: 1234
/// read() // traceID: 1234
///
/// async let id = read() // async let child task, traceID: 1234
///
/// await withTaskGroup(of: String.self) { group in
/// group.addTask { read() } // task group child task, traceID: 1234
/// return await group.next()!
/// }
///
/// Task { // unstructured tasks do inherit task locals by copying
/// read() // traceID: 1234
/// }
///
/// Task.detached { // detached tasks do not inherit task-local values
/// read() // traceID: nil
/// }
/// }
///
/// - SeeAlso: ``TaskLocal-macro``
@available(SwiftStdlib 5.1, *)
public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible {
let defaultValue: Value
public init(wrappedValue defaultValue: Value) {
self.defaultValue = defaultValue
}
@_alwaysEmitIntoClient
var key: Builtin.RawPointer {
unsafeBitCast(self, to: Builtin.RawPointer.self)
}
/// Gets the value currently bound to this task-local from the current task.
///
/// If no current task is available in the context where this call is made,
/// or if the task-local has no value bound, this will return the `defaultValue`
/// of the task local.
public func get() -> Value {
guard let rawValue = _taskLocalValueGet(key: key) else {
return self.defaultValue
}
// Take the value; The type should be correct by construction
let storagePtr =
rawValue.bindMemory(to: Value.self, capacity: 1)
return UnsafeMutablePointer<Value>(mutating: storagePtr).pointee
}
/// Binds the task-local to the specific value for the duration of the asynchronous operation.
///
/// The value is available throughout the execution of the operation closure,
/// including any `get` operations performed by child-tasks created during the
/// execution of the operation closure.
///
/// If the same task-local is bound multiple times, be it in the same task, or
/// in specific child tasks, the more specific (i.e. "deeper") binding is
/// returned when the value is read.
///
/// If the value is a reference type, it will be retained for the duration of
/// the operation closure.
@inlinable
@discardableResult
@available(SwiftStdlib 5.1, *)
@backDeployed(before: SwiftStdlib 6.0)
public func withValue<R>(_ valueDuringOperation: Value,
operation: () async throws -> R,
isolation: isolated (any Actor)? = #isolation,
file: String = #fileID, line: UInt = #line) async rethrows -> R {
return try await withValueImpl(
valueDuringOperation,
operation: operation,
isolation: isolation,
file: file, line: line)
}
// Note: hack to stage out @_unsafeInheritExecutor forms of various functions
// in favor of #isolation. The _unsafeInheritExecutor_ prefix is meaningful
// to the type checker.
//
// This function also doubles as an ABI-compatibility shim predating the
// introduction of #isolation.
@discardableResult
@_unsafeInheritExecutor // ABI compatibility with Swift 5.1
@available(SwiftStdlib 5.1, *)
@_silgen_name("$ss9TaskLocalC9withValue_9operation4file4lineqd__x_qd__yYaKXESSSutYaKlF")
public func _unsafeInheritExecutor_withValue<R>(
_ valueDuringOperation: Value,
operation: () async throws -> R,
file: String = #fileID, line: UInt = #line
) async rethrows -> R {
return try await withValueImpl(valueDuringOperation, operation: operation, file: file, line: line)
}
/// Implementation for withValue that consumes valueDuringOperation.
///
/// Because _taskLocalValuePush and _taskLocalValuePop involve calls to
/// swift_task_alloc/swift_task_dealloc respectively unbeknownst to the
/// compiler, compiler-emitted calls to swift_task_de/alloc must be avoided
/// in a function that calls them.
///
/// A copy of valueDuringOperation is required because withValue borrows its
/// argument but _taskLocalValuePush consumes its. Because
/// valueDuringOperation is of generic type, its size is not generally known,
/// so such a copy entails a stack allocation and a copy to that allocation.
/// That stack traffic gets lowered to calls to
/// swift_task_alloc/swift_task_deallloc.
///
/// Split the calls _taskLocalValuePush/Pop from the compiler-emitted calls
/// to swift_task_de/alloc for the copy as follows:
/// - withValue contains the compiler-emitted calls swift_task_de/alloc.
/// - withValueImpl contains the calls to _taskLocalValuePush/Pop
@inlinable
@discardableResult
@available(SwiftStdlib 5.1, *)
@backDeployed(before: SwiftStdlib 6.0)
internal func withValueImpl<R>(_ valueDuringOperation: __owned Value,
operation: () async throws -> R,
isolation: isolated (any Actor)?,
file: String = #fileID, line: UInt = #line) async rethrows -> R {
_taskLocalValuePush(key: key, value: consume valueDuringOperation)
defer { _taskLocalValuePop() }
return try await operation()
}
@_silgen_name("$ss9TaskLocalC13withValueImpl_9operation4file4lineqd__xn_qd__yYaKXESSSutYaKlF")
@inlinable
@discardableResult
@_unsafeInheritExecutor // internal for backwards compatibility; though may be able to be removed safely?
@available(SwiftStdlib 5.1, *)
internal func _unsafeInheritExecutor_withValueImpl<R>(
_ valueDuringOperation: __owned Value,
operation: () async throws -> R,
file: String = #fileID, line: UInt = #line
) async rethrows -> R {
_taskLocalValuePush(key: key, value: consume valueDuringOperation)
defer { _taskLocalValuePop() }
return try await operation()
}
/// Binds the task-local to the specific value for the duration of the
/// synchronous operation.
///
/// The value is available throughout the execution of the operation closure,
/// including any `get` operations performed by child-tasks created during the
/// execution of the operation closure.
///
/// If the same task-local is bound multiple times, be it in the same task, or
/// in specific child tasks, the "more specific" binding is returned when the
/// value is read.
///
/// If the value is a reference type, it will be retained for the duration of
/// the operation closure.
@inlinable
@discardableResult
public func withValue<R>(_ valueDuringOperation: Value, operation: () throws -> R,
file: String = #fileID, line: UInt = #line) rethrows -> R {
_taskLocalValuePush(key: key, value: valueDuringOperation)
defer { _taskLocalValuePop() }
return try operation()
}
public var projectedValue: TaskLocal<Value> {
get {
self
}
@available(*, unavailable, message: "use '$myTaskLocal.withValue(_:do:)' instead")
set {
fatalError("Illegal attempt to set a \(Self.self) value, use `withValue(...) { ... }` instead.")
}
}
// This subscript is used to enforce that the property wrapper may only be used
// on static (or rather, "without enclosing instance") properties.
// This is done by marking the `_enclosingInstance` as `Never` which informs
// the type-checker that this property-wrapper never wants to have an enclosing
// instance (it is impossible to declare a property wrapper inside the `Never`
// type).
@available(*, unavailable, message: "property wrappers cannot be instance members")
public static subscript(
_enclosingInstance object: Never,
wrapped wrappedKeyPath: ReferenceWritableKeyPath<Never, Value>,
storage storageKeyPath: ReferenceWritableKeyPath<Never, TaskLocal<Value>>
) -> Value {
get {
}
}
public var wrappedValue: Value {
self.get()
}
public var description: String {
"\(Self.self)(defaultValue: \(self.defaultValue))"
}
}
// ==== ------------------------------------------------------------------------
@available(SwiftStdlib 5.1, *)
@usableFromInline
@_silgen_name("swift_task_localValuePush")
func _taskLocalValuePush<Value>(
key: Builtin.RawPointer/*: Key*/,
value: __owned Value
) // where Key: TaskLocal
@available(SwiftStdlib 5.1, *)
@usableFromInline
@_silgen_name("swift_task_localValuePop")
func _taskLocalValuePop()
@available(SwiftStdlib 5.1, *)
@_silgen_name("swift_task_localValueGet")
func _taskLocalValueGet(
key: Builtin.RawPointer/*Key*/
) -> UnsafeMutableRawPointer? // where Key: TaskLocal
@available(SwiftStdlib 5.1, *)
@_silgen_name("swift_task_localsCopyTo")
func _taskLocalsCopy(
to target: Builtin.NativeObject
)
// ==== Checks -----------------------------------------------------------------
@usableFromInline
@available(SwiftStdlib 5.1, *)
@available(*, deprecated, message: "The situation diagnosed by this is not handled gracefully rather than by crashing")
func _checkIllegalTaskLocalBindingWithinWithTaskGroup(file: String, line: UInt) {
if _taskHasTaskGroupStatusRecord() {
file.withCString { _fileStart in
_reportIllegalTaskLocalBindingWithinWithTaskGroup(
_fileStart, file.count, true, line)
}
}
}
@usableFromInline
@available(SwiftStdlib 5.1, *)
@available(*, deprecated, message: "The situation diagnosed by this is not handled gracefully rather than by crashing")
@_silgen_name("swift_task_reportIllegalTaskLocalBindingWithinWithTaskGroup")
func _reportIllegalTaskLocalBindingWithinWithTaskGroup(
_ _filenameStart: UnsafePointer<Int8>,
_ _filenameLength: Int,
_ _filenameIsASCII: Bool,
_ _line: UInt)
|