Exemplo n.º 1
0
bool RefBase::weakref_type::attemptIncStrong(const void* id)
{
    incWeak(id);
    
    weakref_impl* const impl = static_cast<weakref_impl*>(this);
    int32_t curCount = impl->mStrong.load(std::memory_order_relaxed);

    ALOG_ASSERT(curCount >= 0,
            "attemptIncStrong called on %p after underflow", this);

    while (curCount > 0 && curCount != INITIAL_STRONG_VALUE) {
        // we're in the easy/common case of promoting a weak-reference
        // from an existing strong reference.
        if (impl->mStrong.compare_exchange_weak(curCount, curCount+1,
                std::memory_order_relaxed)) {
            break;
        }
        // the strong count has changed on us, we need to re-assert our
        // situation. curCount was updated by compare_exchange_weak.
    }
    
    if (curCount <= 0 || curCount == INITIAL_STRONG_VALUE) {
        // we're now in the harder case of either:
        // - there never was a strong reference on us
        // - or, all strong references have been released
        int32_t flags = impl->mFlags.load(std::memory_order_relaxed);
        if ((flags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
            // this object has a "normal" life-time, i.e.: it gets destroyed
            // when the last strong reference goes away
            if (curCount <= 0) {
                // the last strong-reference got released, the object cannot
                // be revived.
                decWeak(id);
                return false;
            }

            // here, curCount == INITIAL_STRONG_VALUE, which means
            // there never was a strong-reference, so we can try to
            // promote this object; we need to do that atomically.
            while (curCount > 0) {
                if (impl->mStrong.compare_exchange_weak(curCount, curCount+1,
                        std::memory_order_relaxed)) {
                    break;
                }
                // the strong count has changed on us, we need to re-assert our
                // situation (e.g.: another thread has inc/decStrong'ed us)
                // curCount has been updated.
            }

            if (curCount <= 0) {
                // promote() failed, some other thread destroyed us in the
                // meantime (i.e.: strong count reached zero).
                decWeak(id);
                return false;
            }
        } else {
            // this object has an "extended" life-time, i.e.: it can be
            // revived from a weak-reference only.
            // Ask the object's implementation if it agrees to be revived
            if (!impl->mBase->onIncStrongAttempted(FIRST_INC_STRONG, id)) {
                // it didn't so give-up.
                decWeak(id);
                return false;
            }
            // grab a strong-reference, which is always safe due to the
            // extended life-time.
            curCount = impl->mStrong.fetch_add(1, std::memory_order_relaxed);
            // If the strong reference count has already been incremented by
            // someone else, the implementor of onIncStrongAttempted() is holding
            // an unneeded reference.  So call onLastStrongRef() here to remove it.
            // (No, this is not pretty.)  Note that we MUST NOT do this if we
            // are in fact acquiring the first reference.
            if (curCount != 0 && curCount != INITIAL_STRONG_VALUE) {
                impl->mBase->onLastStrongRef(id);
            }
        }
    }
    
    impl->addStrongRef(id);

#if PRINT_REFS
    ALOGD("attemptIncStrong of %p from %p: cnt=%d\n", this, id, curCount);
#endif

    // curCount is the value of mStrong before we incremented it.
    // Now we need to fix-up the count if it was INITIAL_STRONG_VALUE.
    // This must be done safely, i.e.: handle the case where several threads
    // were here in attemptIncStrong().
    // curCount > INITIAL_STRONG_VALUE is OK, and can happen if we're doing
    // this in the middle of another incStrong.  The subtraction is handled
    // by the thread that started with INITIAL_STRONG_VALUE.
    if (curCount == INITIAL_STRONG_VALUE) {
        impl->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
                std::memory_order_relaxed);
    }

    return true;
}
Exemplo n.º 2
0
bool RefBase::weakref_type::attemptIncStrong(const void* id)
{
    incWeak(id);
    
    weakref_impl* const impl = static_cast<weakref_impl*>(this);
    int32_t curCount = impl->mStrong;

    ALOG_ASSERT(curCount >= 0,
            "attemptIncStrong called on %p after underflow", this);

    while (curCount > 0 && curCount != INITIAL_STRONG_VALUE) {
        // we're in the easy/common case of promoting a weak-reference
        // from an existing strong reference.
        if (android_atomic_cmpxchg(curCount, curCount+1, &impl->mStrong) == 0) {
            break;
        }
        // the strong count has changed on us, we need to re-assert our
        // situation.
        curCount = impl->mStrong;
    }
    
    if (curCount <= 0 || curCount == INITIAL_STRONG_VALUE) {
        // we're now in the harder case of either:
        // - there never was a strong reference on us
        // - or, all strong references have been released
        if ((impl->mFlags&OBJECT_LIFETIME_WEAK) == OBJECT_LIFETIME_STRONG) {
            // this object has a "normal" life-time, i.e.: it gets destroyed
            // when the last strong reference goes away
            if (curCount <= 0) {
                // the last strong-reference got released, the object cannot
                // be revived.
                decWeak(id);
                return false;
            }

            // here, curCount == INITIAL_STRONG_VALUE, which means
            // there never was a strong-reference, so we can try to
            // promote this object; we need to do that atomically.
            while (curCount > 0) {
                if (android_atomic_cmpxchg(curCount, curCount + 1,
                        &impl->mStrong) == 0) {
                    break;
                }
                // the strong count has changed on us, we need to re-assert our
                // situation (e.g.: another thread has inc/decStrong'ed us)
                curCount = impl->mStrong;
            }

            if (curCount <= 0) {
                // promote() failed, some other thread destroyed us in the
                // meantime (i.e.: strong count reached zero).
                decWeak(id);
                return false;
            }
        } else {
            // this object has an "extended" life-time, i.e.: it can be
            // revived from a weak-reference only.
            // Ask the object's implementation if it agrees to be revived
            if (!impl->mBase->onIncStrongAttempted(FIRST_INC_STRONG, id)) {
                // it didn't so give-up.
                decWeak(id);
                return false;
            }
            // grab a strong-reference, which is always safe due to the
            // extended life-time.
            curCount = android_atomic_inc(&impl->mStrong);
        }

        // If the strong reference count has already been incremented by
        // someone else, the implementor of onIncStrongAttempted() is holding
        // an unneeded reference.  So call onLastStrongRef() here to remove it.
        // (No, this is not pretty.)  Note that we MUST NOT do this if we
        // are in fact acquiring the first reference.
        if (curCount > 0 && curCount < INITIAL_STRONG_VALUE) {
            impl->mBase->onLastStrongRef(id);
        }
    }
    
    impl->addStrongRef(id);

#if PRINT_REFS
    ALOGD("attemptIncStrong of %p from %p: cnt=%d\n", this, id, curCount);
#endif

    // now we need to fix-up the count if it was INITIAL_STRONG_VALUE
    // this must be done safely, i.e.: handle the case where several threads
    // were here in attemptIncStrong().
    curCount = impl->mStrong;
    while (curCount >= INITIAL_STRONG_VALUE) {
        ALOG_ASSERT(curCount > INITIAL_STRONG_VALUE,
                "attemptIncStrong in %p underflowed to INITIAL_STRONG_VALUE",
                this);
        if (android_atomic_cmpxchg(curCount, curCount-INITIAL_STRONG_VALUE,
                &impl->mStrong) == 0) {
            break;
        }
        // the strong-count changed on us, we need to re-assert the situation,
        // for e.g.: it's possible the fix-up happened in another thread.
        curCount = impl->mStrong;
    }

    return true;
}
Exemplo n.º 3
0
bool RefBase::weakref_type::attemptIncStrong(const void* id)
{
    incWeak(id);
    
    weakref_impl* const impl = static_cast<weakref_impl*>(this);
    
    int32_t curCount = impl->mStrong;
    ALOG_ASSERT(curCount >= 0, "attemptIncStrong called on %p after underflow",
               this);
    while (curCount > 0 && curCount != INITIAL_STRONG_VALUE) {
        if (android_atomic_cmpxchg(curCount, curCount+1, &impl->mStrong) == 0) {
            break;
        }
        curCount = impl->mStrong;
    }
    
    if (curCount <= 0 || curCount == INITIAL_STRONG_VALUE) {
        bool allow;
        if (curCount == INITIAL_STRONG_VALUE) {
            // Attempting to acquire first strong reference...  this is allowed
            // if the object does NOT have a longer lifetime (meaning the
            // implementation doesn't need to see this), or if the implementation
            // allows it to happen.
            allow = (impl->mFlags&OBJECT_LIFETIME_WEAK) != OBJECT_LIFETIME_WEAK
                  || impl->mBase->onIncStrongAttempted(FIRST_INC_STRONG, id);
        } else {
            // Attempting to revive the object...  this is allowed
            // if the object DOES have a longer lifetime (so we can safely
            // call the object with only a weak ref) and the implementation
            // allows it to happen.
            allow = (impl->mFlags&OBJECT_LIFETIME_WEAK) == OBJECT_LIFETIME_WEAK
                  && impl->mBase->onIncStrongAttempted(FIRST_INC_STRONG, id);
        }
        if (!allow) {
            decWeak(id);
            return false;
        }
        curCount = android_atomic_inc(&impl->mStrong);

        // If the strong reference count has already been incremented by
        // someone else, the implementor of onIncStrongAttempted() is holding
        // an unneeded reference.  So call onLastStrongRef() here to remove it.
        // (No, this is not pretty.)  Note that we MUST NOT do this if we
        // are in fact acquiring the first reference.
        if (curCount > 0 && curCount < INITIAL_STRONG_VALUE) {
            impl->mBase->onLastStrongRef(id);
        }
    }
    
    impl->addStrongRef(id);

#if PRINT_REFS
    ALOGD("attemptIncStrong of %p from %p: cnt=%d\n", this, id, curCount);
#endif

    if (curCount == INITIAL_STRONG_VALUE) {
        android_atomic_add(-INITIAL_STRONG_VALUE, &impl->mStrong);
        impl->mBase->onFirstRef();
    }
    
    return true;
}