Unfair lock swift wrapper

UnfairLock.swift

/// Low-level lock that allows waiters to block efficiently on contention.
///
/// Based on `os_unfair_lock_s`
public class UnfairLock {
  // MARK: - Instance variables

  private var unfairLock = os_unfair_lock_s()

  // MARK: - Public

  public init() {
  }

  public func lock() {
    os_unfair_lock_lock(&unfairLock)
  }

  public func unlock() {
    os_unfair_lock_unlock(&unfairLock)
  }

  public func lock<T>(block: () throws -> T) rethrows -> T {
    lock()
    defer {
      unlock()
    }
    return try block()
  }
}