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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift open source project
//
// Copyright (c) 2025 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
/// Lock intended for use within an actor in order to prevent reentrancy in actor methods which themselves contain suspension points.
public actor ActorLock {
private var busy = false
private var queue: ArraySlice<CheckedContinuation<(), Never>> = []
public init() {
}
public func withLock<T: Sendable, E>(_ body: sending () async throws(E) -> T) async throws(E) -> T {
while busy {
await withCheckedContinuation { cc in
queue.append(cc)
}
}
busy = true
defer {
busy = false
if let next = queue.popFirst() {
next.resume(returning: ())
} else {
queue = [] // reallocate buffer if it's empty
}
}
return try await body()
}
}
/// Small concurrency-compatible wrapper to provide only locked, non-reentrant access to its value.
public final class AsyncLockedValue<Wrapped: Sendable> {
@usableFromInline let lock = ActorLock()
/// Don't use this from outside this class. Is internal to be inlinable.
@usableFromInline var value: Wrapped
public init(_ value: Wrapped) {
self.value = value
}
@discardableResult @inlinable
public func withLock<Result: Sendable, E>(_ block: sending (inout Wrapped) async throws(E) -> Result) async throws(E) -> Result {
return try await lock.withLock { () throws(E) -> Result in try await block(&value) }
}
}
extension AsyncLockedValue: @unchecked Sendable where Wrapped: Sendable {
}
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