iOS～AutoRelease 理解
- 官方文档
1、About Memory Management
2、Using Autorelease Pool Blocks
3、Transitioning to ARC Release Notes - Clang 8 documentation 编译器官方文档
4、Objective-C Automatic Reference Counting (ARC)--Clang 8 documentation - 大V的Blog
5、黑幕背后的Autorelease--sunnyxx
6、深入理解 Autorelease--掘金
AutoRelease相关链接的读后感：通过调用[obj autorelease]来延迟obj内存的释放，但是通过嵌套的Autorelease Pool来提前大量局部变量的内存的释放。
1、常见的问题
- Autorelease对象什么时候释放？
- ARC和MRC的差别？
- Autorelease的常见用法？
// NSObject 声明文件
@protocol NSObject
- (instancetype)retain OBJC_ARC_UNAVAILABLE;
- (oneway void)release OBJC_ARC_UNAVAILABLE;
- (instancetype)autorelease OBJC_ARC_UNAVAILABLE;
- (NSUInteger)retainCount OBJC_ARC_UNAVAILABLE;
@end
2、[obj autorelease] 的方法调用 和 Autorelease Pool Blocks 的 区别和联系？
这两者本来是没什么可以混淆的地方，但是提到"自动释放池"的时候,下意识的就会搞混，切记区分"方法调用"和"Block"。
首先，在MRC中，调用[obj autorelease]来延迟内存的释放是一件简单自然的事, 对象调用 [obj autorelease] 才会入池。
而"自动释放池块"提供了一种机制，在这种机制中，您可以放弃对象的所有权，但避免立即释放它(例如当您从方法返回对象时)。通常，您不需要创建自己的自动释放池块，但是在某些情况下，您必须这样做，或者这样做是有益的。
Autorelease pool blocks provide a mechanism whereby you can relinquish ownership of an object, but avoid the possibility of it being deallocated immediately (such as when you return an object from a method). Typically, you don’t need to create your own autorelease pool blocks, but there are some situations in which either you must or it is beneficial to do so.
3、@autoreleasepool{}的原理
AutoreleasePoolPage
void *context = objc_autoreleasePoolPush();
// {}中的代码
objc_autoreleasePoolPop(context);
嵌套的AutoreleasePool：嵌套的栈
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4、Ownership Policy Is Implemented Using Retain Counts
The ownership policy is implemented through reference counting—typically called “retain count” after the [retain] method. Each object has a retain count.
-
When you create an object, it has a retain count of 1.
-
When you send an object a
[retain]message, its retain count is incremented by 1. -
When you send an object a
[release]message, its retain count is decremented by 1. -
When you send an object a
[autorelease]message, its retain count is decremented by 1 at the end of the current autorelease pool block. -
If an object’s retain count is reduced to zero, it is deallocated.
5、 autorelease
- (id)
autorelease
Adds the receiver to the current autorelease pool and returns self. You add an object to an autorelease pool so that it will receive a release message-and thus might be deallocated-when the pool is destroyed.
6、three occasions when you might use your own autorelease pool blocks:
-
If you are writing a program that is not based on a UI framework, such as a command-line tool.
-
If you write a loop that creates many temporary objects.
You may use an autorelease pool block inside the loop to dispose of those objects before the next iteration. Using an autorelease pool block in the loop helps to reduce the maximum memory footprint of the application.
-
If you spawn a secondary thread.
You must create your own autorelease pool block as soon as the thread begins executing; otherwise, your application will leak objects.
(See Autorelease Pool Blocks and Threads for details.)
译： 什么时候用 AutoreleasePool
- 写基于命令行的程序时，就是没有 UI 框架时，如 AppKit 等 Cocoa 框架。
- 写循环，循环里面包含了大量临时创建的对象。
- 创建了新的线程。
- 长时间在后台运行的任务。
7、什么对象会自动加入 autoreleasepool ：
- MRC 下需要对象调用 autorelease 才会入池, ARC 下可以通过 __autoreleasing 修饰符，否则的话看方法名，通过调用 alloc/new/copy/mutablecopy
以外的方法取得的对象，编译器帮我们自动加入 autoreleasepool。 (使用 alloc/new/copy/mutablecopy 方法进行初始化时，由系统管理对象，在适当的位置 release，不加入 autoreleasepool )。 - 使用 array 会自动将返回对象注册到 autoreleasepool。
- __weak 修饰的对象，为了保证在引用时不被废弃，会注册到 autoreleasepool 中。
- id 的指针或对象的指针，在没有显式指定时会被注册到 autoreleasepool 中。
