ARC是否支持调度队列? [英] Does ARC support dispatch queues?

问题描述

我正在阅读Apple的有关调度队列的内存管理"的文档:

I'm reading apple's documentation about "Memory Management for Dispatch Queues":

即使实现垃圾收集应用程序，也必须仍然保留和释放调度队列和其他调度对象. Grand Central Dispatch不支持垃圾回收模型来回收内存.

Even if you implement a garbage-collected application, you must still retain and release your dispatch queues and other dispatch objects. Grand Central Dispatch does not support the garbage collection model for reclaiming memory.

我知道ARC不是垃圾收集器，但是我想确定我不需要dispatch_retain和dispatch_release我的dispatch_queue_t

I know that ARC is not a garbage collector but I'd like to be sure that I don't need to dispatch_retain and dispatch_release my dispatch_queue_t

推荐答案

简短的答案:是的，ARC保留并释放了调度队列.

而现在，答案很长……

The short answer: YES, ARC retains and releases dispatch queues.

And now for the long answer…

您需要在队列上使用dispatch_retain和dispatch_release. ARC不管理它们.

You need to use dispatch_retain and dispatch_release on your queue. ARC does not manage them.

ARC将为您管理队列.如果启用了ARC，则不需要(也不能)使用dispatch_retain或dispatch_release.

ARC will manage your queue for you. You do not need to (and cannot) use dispatch_retain or dispatch_release if ARC is enabled.

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. <os/object.h>头文件中对此进行了记录:

Starting in the iOS 6.0 SDK and the Mac OS X 10.8 SDK, every dispatch object (including a dispatch_queue_t) is also an Objective-C object. This is documented in the <os/object.h> header file:

 * 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.

这意味着您可以将队列存储在NSArray或NSDictionary中，或存储在具有strong，weak，unsafe_unretained，assign或retain属性之一的属性中.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.

This means you can store your queue in an NSArray or NSDictionary, or in a property with one of the strong, weak, unsafe_unretained, assign, or retain attributes. It also means that if you refer to your queue from a block, the block will retain the queue automatically.

因此如果您的部署目标至少是iOS 6.0 或Mac OS X 10.8，并且您已启用ARC ，则ARC将保留并释放您的队列，并且编译器会将使用dispatch_retain或dispatch_release的任何尝试标记为错误.

So if your deployment target is at least iOS 6.0 or Mac OS X 10.8, and you have ARC enabled, ARC will retain and release your queue, and the compiler will flag any attempt to use dispatch_retain or dispatch_release as an error.

如果您的部署目标至少是iOS 6.0 或Mac OS X 10.8，并且您已禁用ARC ，则必须手动保留和释放队列， 通过调用dispatch_retain和dispatch_release，或发送队列retain和release消息(例如[queue retain]和[queue release]).

If your deployment target is at least iOS 6.0 or Mac OS X 10.8, and you have ARC disabled, you must manually retain and release your queue, either by calling dispatch_retain and dispatch_release, or by sending the queue retain and release messages (like [queue retain] and [queue release]).

为了与旧代码库兼容，可以通过定义OS_OBJECT_USE_OBJC至0来防止编译器将队列视为Objective-C对象.例如，您可以将其放在.pch文件中(在任何#import语句之前):

For compatibility with old codebases, you can prevent the compiler from seeing your queue as an Objective-C object by defining OS_OBJECT_USE_OBJC to 0. For example, you can put this in your .pch file (before any #import statements):

#define OS_OBJECT_USE_OBJC 0

，或者您可以在构建设置中将OS_OBJECT_USE_OBJC=0添加为预处理器宏.如果将OS_OBJECT_USE_OBJC设置为0，则ARC将不为您保留或释放您的队列，并且您必须自己使用dispatch_retain和dispatch_release来完成.

or you can add OS_OBJECT_USE_OBJC=0 as a preprocessor macro in your build settings. If you set OS_OBJECT_USE_OBJC to 0, ARC will not retain or release your queue for you, and you will have to do it yourself using dispatch_retain and dispatch_release.

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