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alloc流程图

alloc流程图

作者: MrDemon_ | 来源:发表于2020-09-16 21:23 被阅读0次
    调用alloc流程图
    调用alloc流程图
    源码,关键方法

    源码在objc4-781源码 NSObject.mm类中

    + (id)alloc {
        return _objc_rootAlloc(self);
    }
    _objc_rootAlloc(Class cls)
    {
        return callAlloc(cls, false/*checkNil*/, true/*allocWithZone*/);
    }
    
    callAlloc(Class cls, bool checkNil, bool allocWithZone=false)
    {
    #if __OBJC2__
        if (slowpath(checkNil && !cls)) return nil;
        if (fastpath(!cls->ISA()->hasCustomAWZ())) {
            return _objc_rootAllocWithZone(cls, nil);
        }
    #endif
        // No shortcuts available.
        if (allocWithZone) {
            return ((id(*)(id, SEL, struct _NSZone *))objc_msgSend)(cls, @selector(allocWithZone:), nil);
        }
        return ((id(*)(id, SEL))objc_msgSend)(cls, @selector(alloc));
    }
    
    _objc_rootAllocWithZone(Class cls, malloc_zone_t *zone __unused)
    {
        // allocWithZone under __OBJC2__ ignores the zone parameter
        return _class_createInstanceFromZone(cls, 0, nil,
                                             OBJECT_CONSTRUCT_CALL_BADALLOC);
    }
    
    _class_createInstanceFromZone(Class cls, size_t extraBytes, void *zone,
                                  int construct_flags = OBJECT_CONSTRUCT_NONE,
                                  bool cxxConstruct = true,
                                  size_t *outAllocatedSize = nil)
    {
        ASSERT(cls->isRealized());
    
        // Read class's info bits all at once for performance
        bool hasCxxCtor = cxxConstruct && cls->hasCxxCtor();
        bool hasCxxDtor = cls->hasCxxDtor();
        bool fast = cls->canAllocNonpointer();
        size_t size;
        // 1:要开辟多少内存
        size = cls->instanceSize(extraBytes);
        if (outAllocatedSize) *outAllocatedSize = size;
    
        id obj;
        if (zone) {
            obj = (id)malloc_zone_calloc((malloc_zone_t *)zone, 1, size);
        } else {
            // 2;怎么去申请内存
            obj = (id)calloc(1, size);
        }
        if (slowpath(!obj)) {
            if (construct_flags & OBJECT_CONSTRUCT_CALL_BADALLOC) {
                return _objc_callBadAllocHandler(cls);
            }
            return nil;
        }
    
        // 3:  isa关联到对象
        if (!zone && fast) {
            obj->initInstanceIsa(cls, hasCxxDtor);
        } else {
            // Use raw pointer isa on the assumption that they might be
            // doing something weird with the zone or RR.
            obj->initIsa(cls);
        }
    
        if (fastpath(!hasCxxCtor)) {
            return obj;
        }
    
        construct_flags |= OBJECT_CONSTRUCT_FREE_ONFAILURE;
        return object_cxxConstructFromClass(obj, cls, construct_flags);
    }
    
    //内存对齐方法,16个字节对齐
        size_t instanceSize(size_t extraBytes) const {
            if (fastpath(cache.hasFastInstanceSize(extraBytes))) {
                return cache.fastInstanceSize(extraBytes);
            }
    
            size_t size = alignedInstanceSize() + extraBytes;
            // CF requires all objects be at least 16 bytes.
            if (size < 16) size = 16;
            return size;
        }
    static inline size_t align16(size_t x) {
        return (x + size_t(15)) & ~size_t(15);
    }
    
    init 构造方法 ,工厂设计模式
    + (id)init {
        return (id)self;
    }
    
    new
    + (id)new {
        return [callAlloc(self, false/*checkNil*/) init];
    }
    

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