wehub-resource-sync
60 lines
2.2 KiB
Swift
60 lines
2.2 KiB
Swift
//===----------------------------------------------------------------------===//
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// Copyright © 2025-2026 Apple Inc. and the Containerization project authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//===----------------------------------------------------------------------===//
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/// `AsyncMutex` provides a mutex that protects a piece of data, with the main benefit being that it
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/// is safe to call async methods while holding the lock. This is primarily used in spots
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/// where an actor makes sense, but we may need to ensure we don't fall victim to actor
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/// reentrancy issues.
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public actor AsyncMutex<T: Sendable> {
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private final class Box: @unchecked Sendable {
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var value: T
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init(_ value: T) {
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self.value = value
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}
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}
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private var busy = false
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private var queue: ArraySlice<CheckedContinuation<(), Never>> = []
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private let box: Box
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public init(_ initialValue: T) {
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self.box = Box(initialValue)
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}
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/// withLock provides a scoped locking API to run a function while holding the lock.
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/// The protected value is passed to the closure for safe access.
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public func withLock<R: Sendable>(_ body: @Sendable @escaping (inout T) async throws -> R) async rethrows -> R {
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while self.busy {
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await withCheckedContinuation { cc in
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self.queue.append(cc)
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}
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}
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self.busy = true
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defer {
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self.busy = false
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if let next = self.queue.popFirst() {
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next.resume(returning: ())
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} else {
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self.queue = []
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}
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}
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return try await body(&self.box.value)
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}
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}
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