 		_swift_dispatch_group_async(group, self, workItem._block)
 	}
 
+	///
+	/// Submits a work item to a dispatch queue and optionally associates it with a
+	/// dispatch group. The dispatch group may be used to wait for the completion
+	/// of the work items it references.
+	///
+	/// - parameter group: the dispatch group to associate with the submitted
+	/// work item. If this is `nil`, the work item is not associated with a group.
+	/// - parameter flags: flags that control the execution environment of the
+	/// - parameter qos: the QoS at which the work item should be executed.
+	///	Defaults to `DispatchQoS.unspecified`.
+	/// - parameter flags: flags that control the execution environment of the
+	/// work item.
+	/// - parameter execute: The work item to be invoked on the queue.
+	/// - SeeAlso: `sync(execute:)`
+	/// - SeeAlso: `DispatchQoS`
+	/// - SeeAlso: `DispatchWorkItemFlags`
+	///
 	public func async(
 		group: DispatchGroup? = nil,
 		qos: DispatchQoS = .unspecified,

		}
	}

	@available(macOS 10.10, iOS 8.0, *)
	public func asyncAfter(deadline: DispatchTime, execute: DispatchWorkItem) {
		_swift_dispatch_after(deadline.rawValue, self, execute._block)
	}

	@available(macOS 10.10, iOS 8.0, *)
	public func asyncAfter(wallDeadline: DispatchWallTime, execute: DispatchWorkItem) {
		_swift_dispatch_after(wallDeadline.rawValue, self, execute._block)

		_swift_dispatch_sync(self, workItem._block)
	}

	///
	/// Submits a work item for asynchronous execution on a dispatch queue.
	///
	/// `async(execute:)` is the fundamental mechanism for submitting
	/// work items to a dispatch queue.
	///
	/// Calls to `async(execute:)` always return immediately after the work item has
	/// been submitted, and never wait for the work item to be invoked.
	///
	/// The target queue determines whether the work item will be invoked serially or
	/// concurrently with respect to other work items submitted to that same queue.
	/// Serial queues are processed concurrently with respect to each other.
	///
	/// - parameter execute: The work item to be invoked on the queue.
	/// - SeeAlso: `sync(execute:)`
	///
	///
	@available(macOS 10.10, iOS 8.0, *)
	public func async(execute workItem: DispatchWorkItem) {
		// _swift_dispatch_async preserves the @convention(block)
