NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// ...
[pool release];

@autoreleasepool {
    NSMutableArray *channelItemsJSONArray = [NSMutableArray arrayWithContentsOfFile:[self cachedChannelItemsFile]];
    NSArray *items = [self channelItemsJSONArray];
    if (![items writeToFile:[self cachedChannelItemsFile] atomically:YES]) {
        [channelItemsJSONArray writeToFile:[self cachedChannelItemsFile] atomically:YES];
    }
    items = nil;
}

+ (NSArray *)parseString:(NSString *)originalM3U8Str m3u8Host:(NSString *)m3u8url error:(NSError *__autoreleasing *)errorPtr;

struct __AtAutoreleasePool {
    __AtAutoreleasePool() {
        atautoreleasepoolobj = objc_autoreleasePoolPush();
    }
    ~__AtAutoreleasePool() {
        objc_autoreleasePoolPop(atautoreleasepoolobj);
    }
    void * atautoreleasepoolobj;
};

void *
objc_autoreleasePoolPush(void)
{
    return AutoreleasePoolPage::push();
}
void
objc_autoreleasePoolPop(void *ctxt)
{
    AutoreleasePoolPage::pop(ctxt);
}

class AutoreleasePoolPage 
{
    magic_t const magic;                // 校驗page的結(jié)構(gòu)是否完整
    id *next;                           // 指向下一個可以存放autorelease對象的地址
    pthread_t const thread;             // 當(dāng)前所在的線程
    AutoreleasePoolPage * const parent; // 當(dāng)前page的父節(jié)點
    AutoreleasePoolPage *child;         // 當(dāng)前page的子節(jié)點
    uint32_t const depth;               // page的深度
    uint32_t hiwat;
}

@autoreleasepool {
    NSObject *p1 = [[NSObject alloc] init];
    NSObject *p2 = [[NSObject alloc] init];
    @autoreleasepool {
        NSObject *p3 = [[NSObject alloc] init];
        @autoreleasepool {
            NSObject *p4 = [[NSObject alloc] init];
        }
    }
}

static inline void *push() 
{
    id *dest;
    if (DebugPoolAllocation) {
        dest = autoreleaseNewPage(POOL_BOUNDARY);
    } else {
        dest = autoreleaseFast(POOL_BOUNDARY);
    }
    return dest;
}

static inline id *autoreleaseFast(id obj)
{
    AutoreleasePoolPage *page = hotPage();
    if (page && !page->full()) {
        return page->add(obj);
    } else if (page) {
        return autoreleaseFullPage(obj, page);
    } else {
        return autoreleaseNoPage(obj);
    }
}

static __attribute__((noinline))
id *autoreleaseFullPage(id obj, AutoreleasePoolPage *page)
{
    do {
        if (page->child) page = page->child;
        else page = new AutoreleasePoolPage(page);
    } while (page->full());
    setHotPage(page);
    return page->add(obj);
}

static __attribute__((noinline))
id *autoreleaseNoPage(id obj)
{
    AutoreleasePoolPage *page = new AutoreleasePoolPage(nil);
    setHotPage(page);
    if (pushExtraBoundary) {
        page->add(POOL_BOUNDARY);
    }
    return page->add(obj);
}

id *add(id obj)
{
    ASSERT(!full());
    unprotect();
    id *ret = next;  
    *next++ = obj;
    protect();
    return ret;
}

static inline void
pop(void *token)
{
    AutoreleasePoolPage *page;
    id *stop;
    // 1.
    if (token == (void*)EMPTY_POOL_PLACEHOLDER) {
        page = hotPage();
        if (!page) {
            return setHotPage(nil);
        }
        page = coldPage();
        token = page->begin();
    } else {
        page = pageForPointer(token);
    }
    // 2.
    stop = (id *)token;
    if (*stop != POOL_BOUNDARY) {
        if (stop == page->begin()  &&  !page->parent) {
        } else {
            return badPop(token);
        }
    }
    // 3.
    return popPage<false>(token, page, stop);
}

static void
popPage(void *token, AutoreleasePoolPage *page, id *stop)
{
    page->releaseUntil(stop);
    if (page->child) {
        if (page->lessThanHalfFull()) {
            page->child->kill();
        }
        else if (page->child->child) {
            page->child->child->kill();
        }
    }
}

void releaseUntil(id *stop) 
{
    while (this->next != stop) {
        AutoreleasePoolPage *page = hotPage();
        while (page->empty()) {
            page = page->parent;
            setHotPage(page);
        }
        page->unprotect();
        id obj = *--page->next;
        memset((void*)page->next, SCRIBBLE, sizeof(*page->next));
        page->protect();
        if (obj != POOL_BOUNDARY) {
            objc_release(obj);
        }
    }
    setHotPage(this);
}

static inline id autorelease(id obj)
{
    assert(!obj->isTaggedPointer());
    id *dest __unused = autoreleaseFast(obj);
    return obj;
}

static inline AutoreleasePoolPage *hotPage() 
{
    AutoreleasePoolPage *result = (AutoreleasePoolPage *)
        tls_get_direct(key);
    if ((id *)result == EMPTY_POOL_PLACEHOLDER) return nil;
    if (result) result->fastcheck();
    return result;
}

# define EMPTY_POOL_PLACEHOLDER ((id*)1)

static inline AutoreleasePoolPage *coldPage() 
{
    AutoreleasePoolPage *result = hotPage();
    if (result) {
        while (result->parent) {
            result = result->parent;
            result->fastcheck();
        }
    }
    return result;
}

int main(int argc, const char * argv[]) {
    _objc_autoreleasePoolPrint();     // print1
    @autoreleasepool {
        _objc_autoreleasePoolPrint(); // print2
        Person *p1 = [[[Person alloc] init] autorelease];
        Person *p2 = [[[Person alloc] init] autorelease];
        _objc_autoreleasePoolPrint(); // print3
    }
    _objc_autoreleasePoolPrint();     // print4
    return 0;
}

objc[68122]: ############## (print1)
objc[68122]: AUTORELEASE POOLS for thread 0x1000aa5c0
objc[68122]: 0 releases pending. // 當(dāng)前自動釋放池中沒有任何對象
objc[68122]: [0x102802000]  ................  PAGE  (hot) (cold)
objc[68122]: ##############
objc[68122]: ############## (print2)
objc[68122]: AUTORELEASE POOLS for thread 0x1000aa5c0
objc[68122]: 1 releases pending. // 當(dāng)前自動釋放池中有1個對象，這個對象為POOL_BOUNDARY
objc[68122]: [0x102802000]  ................  PAGE  (hot) (cold)
objc[68122]: [0x102802038]  ################  POOL 0x102802038  //POOL_BOUNDARY
objc[68122]: ##############
objc[68122]: ############## (print3)
objc[68122]: AUTORELEASE POOLS for thread 0x1000aa5c0
objc[68122]: 3 releases pending. // 當(dāng)前自動釋放池中有3個對象
objc[68122]: [0x102802000]  ................  PAGE  (hot) (cold)
objc[68122]: [0x102802038]  ################  POOL 0x102802038  //POOL_BOUNDARY
objc[68122]: [0x102802040]       0x100704a10  HTPerson          //p1
objc[68122]: [0x102802048]       0x10075cc30  HTPerson          //p2
objc[68122]: ##############
objc[68156]: ############## (print4)
objc[68156]: AUTORELEASE POOLS for thread 0x1000aa5c0
objc[68156]: 0 releases pending. // 當(dāng)前自動釋放池中沒有任何對象，因為@autoreleasepool作用域結(jié)束，調(diào)用pop方法釋放了對象
objc[68156]: [0x100810000]  ................  PAGE  (hot) (cold)
objc[68156]: ##############

int main(int argc, char * argv[]) {
    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

// activities = 0x1，kCFRunLoopEntry
<CFRunLoopObserver 0x60000012f000 [0x1135c2bb0]>{valid = Yes, activities = 0x1, repeats = Yes, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x10eee6276)}
// activities = 0xa0，kCFRunLoopBeforeWaiting | kCFRunLoopExit
<CFRunLoopObserver 0x60000012ef60 [0x1135c2bb0]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x10eee6276)}