status_t BufferLayerConsumer::acquireBufferLocked(BufferItem* item, nsecs_t presentWhen,
                                                  uint64_t maxFrameNumber) {
    status_t err = ConsumerBase::acquireBufferLocked(item, presentWhen, maxFrameNumber);
    if (err != NO_ERROR) {
        return err;
    }

    // If item->mGraphicBuffer is not null, this buffer has not been acquired
    // before, so we need to clean up old references.
    if (item->mGraphicBuffer != nullptr) {
        std::lock_guard<std::mutex> lock(mImagesMutex);
        if (mImages[item->mSlot] == nullptr || mImages[item->mSlot]->graphicBuffer() == nullptr ||
            mImages[item->mSlot]->graphicBuffer()->getId() != item->mGraphicBuffer->getId()) {
            mImages[item->mSlot] = std::make_shared<Image>(item->mGraphicBuffer, mRE);
        }
    }

    return NO_ERROR;
}

• 实际上调用的是 ConsumerBase::acquireBufferLocked()。
• 如果 mGraphicBuffer 不空，说明该 buffer 需要更新，更新 mImages 中的引用。
• 在 BufferQueueConsumer::acquireBuffer() 中如果 BufferSlot 的 mAcquireCalled 是 true，则说明消费者已经缓存了 GraphicBuffer，所以 BufferItem::mGraphicBuffer 设置为空指针。