android C++ weakref_impl对象标志位的作用

当mFlags 为OBJECT_LIFETIME_STRONG 时，强引用计数为0时，销毁对象

当mFlags为OBJECT_LIFETIME_WEAK时，强引用计数为0时，不销毁对象，弱引用减为0时，才销毁对象，由于弱引用计数 >= 强引用计数，所以OBJECT_LIFETIME_WEAK延长了对象的存在时间，下面的代码说明了这种情况。当mWeak == 0 且 mFlags == OBJECT_LIFETIME_WEAK时，释放目标对象。

void RefBase::weakref_type::decWeak(const void* id)

{

const int32_t c = android_atomic_dec(&impl->mWeak);

if (c != 1) return;

 

         if ((impl->mFlags&OBJECT_LIFETIME_WEAK) == OBJECT_LIFETIME_STRONG) {

        …

    } else {

        // less common case: lifetime is OBJECT_LIFETIME_{WEAK|FOREVER}

        impl->mBase->onLastWeakRef(id);

        if ((impl->mFlags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_WEAK) {

            // this is the OBJECT_LIFETIME_WEAK case. The last weak-reference

            // is gone, we can destroy the object.

            delete impl->mBase;

        }

    }

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