android C++ weakref_impl對象標誌位的作用

當mFlags 為OBJECT_LIFETIME_STRONG 時，強引用計數為0時，銷毀對象

當mFlags為OBJECT_LIFETIME_WEAK時，強引用計數為0時，不銷毀對象，弱引用減為0時，才銷毀對象，由於弱引用計數 >= 強引用計數，所以OBJECT_LIFETIME_WEAK延長了對象的存在時間，下面的代碼說明了這種情況。當mWeak == 0 且 mFlags == OBJECT_LIFETIME_WEAK時，釋放目標對象。

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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