Kingfisher/Sources/ThreadHelper.swift

//
//  ThreadHelper.swift
//  Kingfisher
//
//  Created by Wei Wang on 15/10/9.
//
//  Copyright (c) 2016 Wei Wang <onevcat@gmail.com>
//
//  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.
//
//  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

func dispatch_async_safely_to_main_queue(block: ()->()) {
    dispatch_async_safely_to_queue(dispatch_get_main_queue(), block)
}

// This method will dispatch the `block` to a specified `queue`.
// If the `queue` is the main queue, and current thread is main thread, the block 
// will be invoked immediately instead of being dispatched.
func dispatch_async_safely_to_queue(queue: dispatch_queue_t, _ block: ()->()) {
    if queue === dispatch_get_main_queue() && NSThread.isMainThread() {
        block()
    } else {
        dispatch_async(queue) {
            block()
        }
    }
}