Answers:
现在长答案...
您需要在队列上使用dispatch_retain和dispatch_release。ARC不管理它们。
ARC将为您管理队列。您不需要（也不能）使用，dispatch_retain或者dispatch_release是否启用了ARC。
从iOS 6.0 SDK和Mac OS X 10.8 SDK开始，每个调度对象（包括dispatch_queue_t）也是一个Objective-C对象。记录在<os/object.h>头文件中：
* By default, libSystem objects such as GCD and XPC objects are declared as
* Objective-C types when building with an Objective-C compiler. This allows
* them to participate in ARC, in RR management by the Blocks runtime and in
* leaks checking by the static analyzer, and enables them to be added to Cocoa
* collections.
*
* NOTE: this requires explicit cancellation of dispatch sources and xpc
* connections whose handler blocks capture the source/connection object,
* resp. ensuring that such captures do not form retain cycles (e.g. by
* declaring the source as __weak).
*
* To opt-out of this default behavior, add -DOS_OBJECT_USE_OBJC=0 to your
* compiler flags.
*
* This mode requires a platform with the modern Objective-C runtime, the
* Objective-C GC compiler option to be disabled, and at least a Mac OS X 10.8
* or iOS 6.0 deployment target.
这意味着你可以把你的队列中的NSArray或NSDictionary，或与一个属性strong，weak，unsafe_unretained，assign，或retain属性。这也意味着，如果您从某个块中引用队列，该块将自动保留该队列。
因此，如果您的部署目标至少是iOS 6.0或Mac OS X 10.8，并且已启用 ARC，则ARC将保留并释放您的队列，并且编译器将标记任何尝试使用dispatch_retain或dispatch_release作为错误。
如果您的部署目标是至少6.0的iOS或Mac OS X 10.8，和你有ARC禁用，您必须手动保留和释放你的队列或者通过调用dispatch_retain和dispatch_release，或通过发送队列retain和release消息（像[queue retain]和[queue release]）。
为了与旧代码库兼容，可以通过定义OS_OBJECT_USE_OBJC为，防止编译器将队列视为Objective-C对象0。例如，您可以将其放在.pch文件中（在任何#import语句之前）：
#define OS_OBJECT_USE_OBJC 0或者您可以OS_OBJECT_USE_OBJC=0在构建设置中添加为预处理器宏。如果设置OS_OBJECT_USE_OBJC为0，ARC将不会为您保留或释放您的队列，您必须使用dispatch_retain和自己进行dispatch_release。
dispatch_release 和 NULL你的5.1的目标dealloc代码。否则，某些东西（由编译器生成的代码？运行时本身？）将尝试第二次释放该对象。