关于GCD时，
QOS_CLASS_BACKGROUND
感觉是属于QOS＝＝quality of service系列的
和
DISPATCH_QUEUE_PRIORITY_BACKGROUND
不知道是什么关系
后来通过点击
let backgroundQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0) |
中的dispatch_get_global_queue看到源码：
/*! * @function dispatch_get_global_queue * * @abstract * Returns a well-known global concurrent queue of a given quality of service * class. * * @discussion * The well-known global concurrent queues may not be modified. Calls to * dispatch_suspend(), dispatch_resume(), dispatch_set_context(), etc., will * have no effect when used with queues returned by this function. * * @param identifier * A quality of service class defined in qos_class_t or a priority defined in * dispatch_queue_priority_t. * * It is recommended to use quality of service class values to identify the * well-known global concurrent queues: * – QOS_CLASS_USER_INTERACTIVE * – QOS_CLASS_USER_INITIATED * – QOS_CLASS_DEFAULT * – QOS_CLASS_UTILITY * – QOS_CLASS_BACKGROUND * * The global concurrent queues may still be identified by their priority, * which map to the following QOS classes: * – DISPATCH_QUEUE_PRIORITY_HIGH: QOS_CLASS_USER_INITIATED * – DISPATCH_QUEUE_PRIORITY_DEFAULT: QOS_CLASS_DEFAULT * – DISPATCH_QUEUE_PRIORITY_LOW: QOS_CLASS_UTILITY * – DISPATCH_QUEUE_PRIORITY_BACKGROUND: QOS_CLASS_BACKGROUND * * @param flags * Reserved for future use. Passing any value other than zero may result in * a NULL return value. * * @result * Returns the requested global queue or NULL if the requested global queue * does not exist. */ @available(iOS 4.0, *) @warn_unused_result public func dispatch_get_global_queue(identifier: Int, _ flags: UInt) -> dispatch_queue_t! |
可以看出来是：
DISPATCH_QUEUE_PRIORITY_HIGH＝＝QOS_CLASS_USER_INITIATED
DISPATCH_QUEUE_PRIORITY_DEFAULT＝＝ QOS_CLASS_DEFAULT
DISPATCH_QUEUE_PRIORITY_LOW＝＝ QOS_CLASS_UTILITY
DISPATCH_QUEUE_PRIORITY_BACKGROUND＝＝QOS_CLASS_BACKGROUND
的。
建议使用QOS系列的。
所以建议使用：
let backgroundQueue = dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0) |
而不是：
let backgroundQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0) |
转载请注明：在路上 » 【整理】swift中QOS_CLASS_BACKGROUND vs DISPATCH_QUEUE_PRIORITY_BACKGROUND