该函数在 BLASTBufferQueue::acquireNextBufferLocked() 中调用 BufferStateLayer::setBuffer() 时作为参数 releaseBufferCallback 传入。

// Unlike transactionCallbackThunk the release buffer callback does not extend the life of the
// BBQ. This is because if the BBQ is destroyed, then the buffers will be released by the client.
// So we pass in a weak pointer to the BBQ and if it still alive, then we release the buffer.
// Otherwise, this is a no-op.
static void releaseBufferCallbackThunk(wp<BLASTBufferQueue> context, const ReleaseCallbackId& id,
                                       const sp<Fence>& releaseFence, uint32_t transformHint,
                                       uint32_t currentMaxAcquiredBufferCount) {
    sp<BLASTBufferQueue> blastBufferQueue = context.promote();
    if (blastBufferQueue) {
        blastBufferQueue->releaseBufferCallback(id, releaseFence, transformHint,
                                                currentMaxAcquiredBufferCount);
    } else {
        ALOGV("releaseBufferCallbackThunk %s blastBufferQueue is dead", id.to_string().c_str());
    }
}

• 调用 BLASTBufferQueue::releaseBufferCallback()。