isa

在arm64 之前,isa就是一個(gè)普通的指針,它指向classormeta-class
在arm64之后,對(duì)isa進(jìn)行了優(yōu)化,變成了一個(gè)共同體(union)結(jié)構(gòu),還使用位域來存儲(chǔ)更多信息.
先來看一個(gè)例子:新建person類

@interface Person : NSObject

- (void)setTall:(BOOL)tall;
- (void)setRich:(BOOL)rich;
- (void)setHandSome:(BOOL)handSome;

- (BOOL)getTall;
- (BOOL)getRich;
- (BOOL)getHandSome;

@end

再來.m文件

//掩碼 進(jìn)行位運(yùn)算
//#define ISTallMASK  1
//#define ISRichMASK  2
//#define ISHandSomeMASK  4

#define ISTallMASK  (1<<0)
#define ISRichMASK  (1<<1)
#define ISHandSomeMASK  (1<<2)

@interface Person()
{
    char _tallRichHandsome;
}

@end

@implementation Person

- (instancetype)init
{
    self = [super init];
    if (self) {
        //從右至左tall rich handsome
        _tallRichHandsome = 0b00000000;
    }
    return self;
}

- (void)setTall:(BOOL)tall{
    if (tall) {
        // | 或運(yùn)算 有1則為1
        /*
            0000 0001
            0000 0001
         */
        _tallRichHandsome = _tallRichHandsome | ISTallMASK;
    }else{
        /*
            0000 0101
            1111 1110
            先取反 在進(jìn)行&運(yùn)算 保證其他為不變 標(biāo)志位必為0
         */
        _tallRichHandsome = _tallRichHandsome & ~ISTallMASK;
    }
}

- (void)setRich:(BOOL)rich{
    if (rich) {
        _tallRichHandsome = _tallRichHandsome | ISRichMASK;
    }else{
        _tallRichHandsome = _tallRichHandsome & ~ISRichMASK;
    }
}

- (void)setHandSome:(BOOL)handSome{
    if (handSome) {
        _tallRichHandsome = _tallRichHandsome | ISHandSomeMASK;
    }else{
        _tallRichHandsome = _tallRichHandsome & ~ISHandSomeMASK;
    }
}

- (BOOL)getTall{
    //&運(yùn)算  同為1則為1
    /*
     0000 0000
     0000 0001  // 十進(jìn)制1*2^0 = 1
     */
    return !!(_tallRichHandsome & ISTallMASK);
}

- (BOOL)getRich{
    /*
        0000 0000
        0000 0010  // 十進(jìn)制1*2^1 = 2
     */
    return !!(_tallRichHandsome & ISRichMASK);
}

- (BOOL)getHandSome{
    /*
     0000 0000
     0000 0100  // 十進(jìn)制1*2^2 = 4
     */
    return !!(_tallRichHandsome & ISHandSomeMASK);
}

這樣我們就實(shí)現(xiàn)了一個(gè)字節(jié)存儲(chǔ)3個(gè)BOOL變量.如果以后要增加到4個(gè)BOOL變量,不免有些麻煩,接下來優(yōu)化一下.

@interface Person()
{
//    char _tallRichHandsome;
    //位域
    struct {
        char tall :1;//表示只占一位
        char rich :1;
        char handsome :1;
        
    }_tallRichHandsome;
}

@implementation Person

- (void)setTall:(BOOL)tall{
    _tallRichHandsome.tall = tall;
}

- (void)setRich:(BOOL)rich{
  _tallRichHandsome.rich = rich;
}

- (void)setHandSome:(BOOL)handSome{
    _tallRichHandsome.handsome = handSome;
}

- (BOOL)getTall{
//    BOOL isRet = _tallRichHandsome.tall
    //這里強(qiáng)制轉(zhuǎn)換 一個(gè)BOOL 類型是占一個(gè)字節(jié) tall這里是0x01 強(qiáng)轉(zhuǎn)后變 1111 1111 = 255,所以這里需要2次取反拿到正確的值.
    return !!(_tallRichHandsome.tall);
}

- (BOOL)getRich{
    return !!(_tallRichHandsome.rich);
}

- (BOOL)getHandSome{
   return !!(_tallRichHandsome.handsome);

@end

        Person *persn = [[Person alloc]init];
        [persn setTall:YES];
        [persn setRich:NO];
        [persn setHandSome:NO];
        NSLog(@"%d-- %d ---%d",persn.getRich,persn.getTall,persn.getHandSome);
        
(lldb) p/x &(persn->_tallRichHandsome)
((anonymous struct) *) $0 = 0x000000010281f2a8
(lldb) x 0x000000010281f2a8
0x10281f2a8: 01 00 00 00 00 00 00 00 63 46 1b 41 ff 7f 00 00  ........cF.A....
0x10281f2b8: 4a 97 fb 42 ff 7f 00 00 b9 be 52 45 ff 7f 00 00  J..B......RE....

看01 00 00 00 00 00 00 00 第2個(gè)十六進(jìn)制位,轉(zhuǎn)換成二進(jìn)制是0000 0001說明tall被放在最右邊.
接下來看看蘋果的做法

@interface Person()
{
//    位域
    union{

        char bits;
        struct {
            char tall :1;
            char rich :1;
            char handsome :1;
            
        };
        
    }_tallRichHandsome;
}

@end

union是一個(gè)共同體,bits占一個(gè)字節(jié),struct也占一個(gè)字節(jié).
.m文件


- (void)setTall:(BOOL)tall{
    if (tall) {
        _tallRichHandsome.bits = _tallRichHandsome.bits | ISTallMASK;
    }else{
        _tallRichHandsome.bits = _tallRichHandsome.bits & ~ISTallMASK;
    }
}

再來看isa的結(jié)構(gòu)

union isa_t 
{

    Class cls;
    uintptr_t bits;
#   define ISA_MASK        0x0000000ffffffff8ULL
#   define ISA_MAGIC_MASK  0x000003f000000001ULL
#   define ISA_MAGIC_VALUE 0x000001a000000001ULL
    struct {
        uintptr_t nonpointer        : 1;
        uintptr_t has_assoc         : 1;
        uintptr_t has_cxx_dtor      : 1;
        uintptr_t shiftcls          : 33; // MACH_VM_MAX_ADDRESS 0x1000000000
        uintptr_t magic             : 6;
        uintptr_t weakly_referenced : 1;
        uintptr_t deallocating      : 1;
        uintptr_t has_sidetable_rc  : 1;
        uintptr_t extra_rc          : 19;
    };
}

nonpointer
0，代表普通的指針，存儲(chǔ)著Class、Meta-Class對(duì)象的內(nèi)存地址
1，代表優(yōu)化過，使用位域存儲(chǔ)更多的信息
has_assoc
是否有設(shè)置過關(guān)聯(lián)對(duì)象，如果沒有，釋放時(shí)會(huì)更快
has_cxx_dtor
是否有C++的析構(gòu)函數(shù)（.cxx_destruct），如果沒有，釋放時(shí)會(huì)更快
shiftcls
存儲(chǔ)著Class、Meta-Class對(duì)象的內(nèi)存地址信息
magic
用于在調(diào)試時(shí)分辨對(duì)象是否未完成初始化
weakly_referenced
是否有被弱引用指向過，如果沒有，釋放時(shí)會(huì)更快
deallocating
對(duì)象是否正在釋放
extra_rc
里面存儲(chǔ)的值是引用計(jì)數(shù)器減1
has_sidetable_rc
引用計(jì)數(shù)器是否過大無法存儲(chǔ)在isa中
如果為1，那么引用計(jì)數(shù)會(huì)存儲(chǔ)在一個(gè)叫SideTable的類的屬性中

Class結(jié)構(gòu)

struct objc_class  {
    Class ISA;
    Class superclass;
    cache_t cache;             // formerly cache pointer and vtable
    class_data_bits_t bits;    // class_rw_t * plus custom rr/alloc flags
}

bits & FAST_DATA_MASK 得到


//類的初始信息
struct class_ro_t {
    uint32_t flags;
    uint32_t instanceStart;
    uint32_t instanceSize;
#ifdef __LP64__
    uint32_t reserved;
#endif

    const uint8_t * ivarLayout;
    
    const char * name;
    method_list_t * baseMethodList;
    protocol_list_t * baseProtocols;
    const ivar_list_t * ivars;

    const uint8_t * weakIvarLayout;
    property_list_t *baseProperties;

    method_list_t *baseMethods() const {
        return baseMethodList;
    }
};

struct class_rw_t {
    // Be warned that Symbolication knows the layout of this structure.
    uint32_t flags;
    uint32_t version;

    const class_ro_t *ro;

    method_array_t methods;//方法列表
    property_array_t properties;//屬性列表
    protocol_array_t protocols;//協(xié)議列表

    Class firstSubclass;
    Class nextSiblingClass;

    char *demangledName;
{

method_array_t是一個(gè)二維數(shù)組里面最終存放的是method_t

struct method_t {
    SEL name;
    const char *types;
    IMP imp;
}

name; 函數(shù)名
types; 編碼(函數(shù)返回值類型,參數(shù)類型)
imp; 函數(shù)地址(指向函數(shù)的指針)

SEL代表方法\函數(shù)名，一般叫做選擇器，底層結(jié)構(gòu)跟char *類似
可以通過@selector()和sel_registerName()獲得
可以通過sel_getName()和NSStringFromSelector()轉(zhuǎn)成字符串
不同類中相同名字的方法，所對(duì)應(yīng)的方法選擇器是相同的

iOS中提供了一個(gè)叫做@encode的指令，可以將具體的類型表示成字符串編碼

image.png

接下來看看cache_t結(jié)構(gòu)

struct bucket_t {
    cache_key_t _key;// SEL作為key
    IMP _imp;//函數(shù)的內(nèi)存地址
};

struct cache_t {
    struct bucket_t *_buckets;//哈希表
    mask_t _mask;//哈希表長度 - 1
    mask_t _occupied;//已經(jīng)緩存的方法數(shù)量
}

哈希表相關(guān)資料鏈接

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Runtime(一)

Runtime(一)

isa

Class結(jié)構(gòu)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

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Runtime(一)

isa

Class結(jié)構(gòu)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av