内存管理:自动释放池

自动释放池的主要底层数据结构是:__AtAutoreleasePool、AutoreleasePoolPage

调用了autorelease的对象最终都是通过AutoreleasePoolPage对象来管理的

源码分析
clang重写@autoreleasepool
objc4源码:NSObject.mm

autoreleasepool

开始调用objc_autoreleasePoolPush
结束调用objc_autoreleasePoolPop

int main(int argc, const char * argv[]) {
    @autoreleasepool {
//        atautoreleasepoolobj = objc_autoreleasePoolPush();
        

        
//        objc_autoreleasePoolPop(atautoreleasepoolobj);
    }
    return 0;
}

AutoreleasePoolPage

每个AutoreleasePoolPage对象占用4096字节内存,除了用来存放它内部的成员变量,剩下的空间用来存放autorelease对象的地址
所有的AutoreleasePoolPage对象通过双向链表的形式连接在一起

image.png

AutoreleasePoolPage的结构

调用push方法会将一个POOL_BOUNDARY入栈,并且返回其存放的内存地址

调用pop方法时传入一个POOL_BOUNDARY的内存地址,会从最后一个入栈的对象开始发送release消息,直到遇到这个POOL_BOUNDARY

id *next指向了下一个能存放autorelease对象地址的区域

/*
 typedef CF_OPTIONS(CFOptionFlags, CFRunLoopActivity) {
 kCFRunLoopEntry = (1UL << 0),  1
 kCFRunLoopBeforeTimers = (1UL << 1), 2
 kCFRunLoopBeforeSources = (1UL << 2), 4
 kCFRunLoopBeforeWaiting = (1UL << 5), 32
 kCFRunLoopAfterWaiting = (1UL << 6), 64
 kCFRunLoopExit = (1UL << 7), 128
 kCFRunLoopAllActivities = 0x0FFFFFFFU
 };
 */

/*
 kCFRunLoopEntry  push
 
 {valid = Yes, activities = 0x1, repeats = Yes, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x103376df2), context = {type = mutable-small, count = 1, values = (\n\t0 : <0x7fd0bf802048>\n)}}
 
 
 kCFRunLoopBeforeWaiting | kCFRunLoopExit
 kCFRunLoopBeforeWaiting pop、push
 kCFRunLoopExit pop
 
 {valid = Yes, activities = 0xa0, repeats = Yes, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x103376df2), context = {type = mutable-small, count = 1, values = (\n\t0 : <0x7fd0bf802048>\n)}}
 */

Runloop和Autorelease

iOS在主线程的Runloop中注册了2个Observer
第1个Observer监听了kCFRunLoopEntry事件,会调用objc_autoreleasePoolPush()
第2个Observer
监听了kCFRunLoopBeforeWaiting事件,会调用objc_autoreleasePoolPop()、objc_autoreleasePoolPush()
监听了kCFRunLoopBeforeExit事件,会调用objc_autoreleasePoolPop()

你可能感兴趣的:(内存管理:自动释放池)