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//
// ResultOperation.swift
// Operations
//
// Created by pronebird on 23/03/2022.
// Copyright © 2022 Mullvad VPN AB. All rights reserved.
//
import Foundation
/// Base class for operations producing result.
open class ResultOperation<Success, Failure: Error>: AsyncOperation {
public typealias Completion = OperationCompletion<Success, Failure>
public typealias CompletionHandler = (Completion) -> Void
private let nslock = NSLock()
private var completionValue: Completion?
private var _completionQueue: DispatchQueue?
private var _completionHandler: CompletionHandler?
private var pendingFinish = false
public var completion: Completion? {
nslock.lock()
defer { nslock.unlock() }
return completionValue
}
public var completionQueue: DispatchQueue? {
get {
nslock.lock()
defer { nslock.unlock() }
return _completionQueue
}
set {
nslock.lock()
_completionQueue = newValue
nslock.unlock()
}
}
public var completionHandler: CompletionHandler? {
get {
nslock.lock()
defer { nslock.unlock() }
return _completionHandler
}
set {
nslock.lock()
defer { nslock.unlock() }
if !pendingFinish {
_completionHandler = newValue
}
}
}
override public init(dispatchQueue: DispatchQueue?) {
super.init(dispatchQueue: dispatchQueue)
}
public init(
dispatchQueue: DispatchQueue?,
completionQueue: DispatchQueue?,
completionHandler: CompletionHandler?
) {
_completionQueue = completionQueue
_completionHandler = completionHandler
super.init(dispatchQueue: dispatchQueue)
}
@available(*, unavailable)
override public func finish() {
_finish(error: nil)
}
@available(*, unavailable)
override public func finish(error: Error?) {
_finish(error: error)
}
open func finish(completion: Completion) {
nslock.lock()
if completionValue == nil {
completionValue = completion
}
nslock.unlock()
_finish(error: completion.error)
}
private func _finish(error: Error?) {
nslock.lock()
// Bail if operation is already finishing.
guard !pendingFinish else {
nslock.unlock()
return
}
// Mark that operation is pending finish.
pendingFinish = true
// Copy completion handler.
let completionHandler = _completionHandler
// Unset completion handler.
_completionHandler = nil
// Copy completion value.
let completion = completionValue ?? .cancelled
// Copy completion queue.
let completionQueue = _completionQueue
nslock.unlock()
let block = {
// Call completion handler.
completionHandler?(completion)
// Finish operation.
super.finish(error: error)
}
if let completionQueue = completionQueue {
completionQueue.async(execute: block)
} else {
block()
}
}
}
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