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# Motivation For AsyncStream we created a custom internal Deque implementation to use for the buffering. This implementation was relatively bare-bones compared to the one in swift-collections. Furthermore, it lacked some methods that we need to implement the new `AsyncStream` APIs that support producer backpressure. # Modification This PR copies over the Deque implementation of swift-collections and makes it internal and non-inlinable. # Result We now have a fully functional Deque.
50 lines
1.7 KiB
Swift
50 lines
1.7 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) 2021 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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//
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//===----------------------------------------------------------------------===//
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/// This file is copied from swift-collections and should not be modified here.
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/// Rather all changes should be made to swift-collections and copied back.
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import Swift
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internal class _DequeBuffer<Element>: ManagedBuffer<_DequeBufferHeader, Element> {
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deinit {
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self.withUnsafeMutablePointers { header, elements in
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header.pointee._checkInvariants()
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let capacity = header.pointee.capacity
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let count = header.pointee.count
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let startSlot = header.pointee.startSlot
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if startSlot.position + count <= capacity {
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(elements + startSlot.position).deinitialize(count: count)
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} else {
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let firstRegion = capacity - startSlot.position
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(elements + startSlot.position).deinitialize(count: firstRegion)
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elements.deinitialize(count: count - firstRegion)
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}
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}
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}
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}
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extension _DequeBuffer: CustomStringConvertible {
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internal var description: String {
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withUnsafeMutablePointerToHeader { "_DequeStorage<\(Element.self)>\($0.pointee)" }
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}
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}
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/// The type-punned empty singleton storage instance.
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internal let _emptyDequeStorage = _DequeBuffer<Void>.create(
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minimumCapacity: 0,
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makingHeaderWith: { _ in
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_DequeBufferHeader(capacity: 0, count: 0, startSlot: .init(at: 0))
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})
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