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// SPDX-License-Identifier: MIT
// Copyright © 2018-2021 WireGuard LLC. All Rights Reserved.
import Foundation
extension Array {
/// Returns an array containing the results of mapping the given closure over the sequence’s
/// elements concurrently.
///
/// - Parameters:
/// - queue: The queue for performing concurrent computations.
/// If the given queue is serial, the values are mapped in a serial fashion.
/// Pass `nil` to perform computations on the current queue.
/// - transform: the block to perform concurrent computations over the given element.
/// - Returns: an array of concurrently computed values.
func concurrentMap<U>(queue: DispatchQueue?, _ transform: (Element) -> U) -> [U] {
var result = [U?](repeating: nil, count: self.count)
let resultQueue = DispatchQueue(label: "ConcurrentMapQueue")
let execute = queue?.sync ?? { $0() }
execute {
DispatchQueue.concurrentPerform(iterations: self.count) { index in
let value = transform(self[index])
resultQueue.sync {
result[index] = value
}
}
}
return result.map { $0! }
}
}
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