閱讀objc4-706中的objc-accessors.mm文件祭椰，會(huì)發(fā)現(xiàn)屬性設(shè)置有以下幾個(gè)方法：
1讯泣、objc_setProperty
2阵漏、objc_setProperty_atomic
3预侯、objc_setProperty_nonatomic
4木羹、objc_setProperty_atomic_copy
5集索、objc_setProperty_nonatomic_copy
最終調(diào)用的都是 reallySetProperty(id self, SEL _cmd, id newValue, ptrdiff_t offset, bool atomic, bool copy, bool mutableCopy) :
spinlock_t & slotlock = PropertyLocks[slot];
slotlock.lock();
oldValue = *slot;
*slot = newValue;
slotlock.unlock();
