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83b8be8ad0
We need this function anyway to escalate process priorities when we set `nice`ness values for them. It also simplifies the task scheduler and I’m hoping that it fixes a non-deterministic failure that causes task priority elevation to not work properly.
61 lines
2.3 KiB
Swift
61 lines
2.3 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) 2014 - 2024 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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/// Runs `operation`. If the task's priority changes while the operation is running, calls `taskPriorityChanged`.
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///
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/// Since Swift Concurrency doesn't support direct observation of a task's priority, this polls the task's priority at
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/// `pollingInterval`.
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/// The function assumes that the original priority of the task is `initialPriority`. If the task priority changed
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/// compared to `initialPriority`, the `taskPriorityChanged` will be called.
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public func withTaskPriorityChangedHandler(
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initialPriority: TaskPriority = Task.currentPriority,
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pollingInterval: Duration = .seconds(0.1),
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@_inheritActorContext operation: @escaping @Sendable () async -> Void,
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taskPriorityChanged: @escaping @Sendable () -> Void
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) async {
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let lastPriority = ThreadSafeBox(initialValue: initialPriority)
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await withTaskGroup(of: Void.self) { taskGroup in
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taskGroup.addTask {
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while true {
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if Task.isCancelled {
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return
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}
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let newPriority = Task.currentPriority
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let didChange = lastPriority.withLock { lastPriority in
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if newPriority != lastPriority {
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lastPriority = newPriority
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return true
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}
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return false
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}
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if didChange {
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taskPriorityChanged()
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}
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do {
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try await Task.sleep(for: pollingInterval)
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} catch {
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break
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}
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}
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}
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taskGroup.addTask {
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await operation()
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}
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// The first task that watches the priority never finishes, so we are effectively await the `operation` task here
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// and cancelling the priority observation task once the operation task is done.
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// We do need to await the observation task as well so that priority escalation also affects the observation task.
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for await _ in taskGroup {
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taskGroup.cancelAll()
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}
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}
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}
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