void SurfaceComposerClient::Transaction::setReleaseBufferCallback(layer_state_t* s,
                                                                  const ReleaseCallbackId& id,
                                                                  ReleaseBufferCallback callback) {
    if (!callback) {
        return;
    }

    if (!s->buffer) {
        ALOGW("Transaction::setReleaseBufferCallback"
              "ignored trying to set a callback on a null buffer.");
        return;
    }

    s->what |= layer_state_t::eReleaseBufferListenerChanged;
    s->releaseBufferListener = TransactionCompletedListener::getIInstance();
    s->releaseCallbackId = id;
    auto listener = TransactionCompletedListener::getInstance();
    listener->setReleaseBufferCallback(id, callback);
}

• 给 layer_state_t 设置 eReleaseBufferListenerChanged、releaseBufferListener 和 releaseCallbackId。
• 调用 TransactionCompletedListener::setReleaseBufferCallback() 把 callback 保存到 mReleaseBufferCallbacks。