This template class make a value can be safe thread

SynchronizedValue.swift

/**
 * Copyright (c) 2017 Razeware LLC
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * Notwithstanding the foregoing, you may not use, copy, modify, merge, publish,
 * distribute, sublicense, create a derivative work, and/or sell copies of the
 * Software in any work that is designed, intended, or marketed for pedagogical or
 * instructional purposes related to programming, coding, application development,
 * or information technology.  Permission for such use, copying, modification,
 * merger, publication, distribution, sublicensing, creation of derivative works,
 * or sale is expressly withheld.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

import Foundation

public class SynchronizedValue<ValueType: Any> {
  
  // MARK: - Properties
  private let queue = DispatchQueue(
    label: "SynchronizedValue(\(type(of: ValueType.self))",
    attributes: .concurrent)
  
  private var backingValue: ValueType
  
  // MARK: - Object Lifecycle
  public init(_ value: ValueType) {
    self.backingValue = value
  }
  
  // MARK: - Safe Accessors
  public func get() -> ValueType {
    var value: ValueType!
    queue.sync { value = backingValue }
    return value
  }
  
  public func set(_ closure: (inout ValueType) -> ()) {
    queue.sync(flags: .barrier) { closure(&backingValue) }
  }
  
  // MARK: - Unsafe Accessors
  public var unsafeValue: ValueType {
    get { return backingValue }
    set { backingValue = newValue }
  }
  
  public func setUnsafeValue(_ closure: (inout ValueType) -> ()) {
    closure(&backingValue)
  }
}