我看了下NSQualityOfServic这个枚举，在iOS8及以上的版本才能用啊

typedef NS_ENUM(NSInteger, NSQualityOfService) {
    /* UserInteractive QoS is used for work directly involved in providing an interactive UI such as processing events or drawing to the screen. */
    NSQualityOfServiceUserInteractive = 0x21,

    /* UserInitiated QoS is used for performing work that has been explicitly requested by the user and for which results must be immediately presented in order to allow for further user interaction.  For example, loading an email after a user has selected it in a message list. */
    NSQualityOfServiceUserInitiated = 0x19,

    /* Utility QoS is used for performing work which the user is unlikely to be immediately waiting for the results.  This work may have been requested by the user or initiated automatically, does not prevent the user from further interaction, often operates at user-visible timescales and may have its progress indicated to the user by a non-modal progress indicator.  This work will run in an energy-efficient manner, in deference to higher QoS work when resources are constrained.  For example, periodic content updates or bulk file operations such as media import. */
    NSQualityOfServiceUtility = 0x11,

    /* Background QoS is used for work that is not user initiated or visible.  In general, a user is unaware that this work is even happening and it will run in the most efficient manner while giving the most deference to higher QoS work.  For example, pre-fetching content, search indexing, backups, and syncing of data with external systems. */
    NSQualityOfServiceBackground = 0x09,

    /* Default QoS indicates the absence of QoS information.  Whenever possible QoS information will be inferred from other sources.  If such inference is not possible, a QoS between UserInitiated and Utility will be used. */
    NSQualityOfServiceDefault = -1
} NS_ENUM_AVAILABLE(10_10, 8_0);

#define MAX_QUEUE_COUNT 32

int count = (int)[NSProcessInfo processInfo].activeProcessorCount; count = count < 1 ? 1 : count > MAX_QUEUE_COUNT ? MAX_QUEUE_COUNT : count;

iPhone在代码上获取处理器个数count为2，而且这个count应该不会超过32吧？

项目是Objective-C++，有很多.mm文件。手动引入后报这个错误，手动把.h.m拖到工程里面的。

Undefined symbols for architecture arm64: "YYDispatchQueueGetForQOS(NSQualityOfService)", referenced from: -[CameraManager queue] in CameraManager.o ld: symbol(s) not found for architecture arm64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

你好，请问 dispatch_async(self.mainQueue, ^{ dispatch_sync(self.subQueue, ^{ NSLog(@"%@", [NSThread currentThread]); 这种，chatMainQueue使用YYDispatchQueuePool的queue，或者使用一个SERIAL的queue，是有创建新的NSThread，这种好像系统控制了资源分配，可是当处理比较长，创建的NSThread越多，内存问题就越大。不知是否有可行办法。 实现非主线程的串行队列，也是想控制其在一个或者固定几个NSThread执行，然后再回到主线程更新UI。