Merge fences when needed for accurate timestamps.

        return OK;

    }

    auto status = mSlots[slot].mFence->getStatus();

    if (status == Fence::Status::Invalid) {

        CB_LOGE("fence has invalid state");

    // Check status of fences first because merging is expensive.

    // Merging an invalid fence with any other fence results in an

    // invalid fence.

    auto currentStatus = mSlots[slot].mFence->getStatus();

    if (currentStatus == Fence::Status::Invalid) {

        CB_LOGE("Existing fence has invalid state");

        return BAD_VALUE;

    }

    if (status == Fence::Status::Signaled) {

    auto incomingStatus = fence->getStatus();

    if (incomingStatus == Fence::Status::Invalid) {

        CB_LOGE("New fence has invalid state");

        mSlots[slot].mFence = fence;

    } else {  // status == Fence::Status::Unsignaled

        return BAD_VALUE;

    }

    // If both fences are signaled or both are unsignaled, we need to merge

    // them to get an accurate timestamp.

    if (currentStatus == incomingStatus) {

        char fenceName[32] = {};

        snprintf(fenceName, 32, "%.28s:%d", mName.string(), slot);

        sp<Fence> mergedFence = Fence::merge(

            return BAD_VALUE;

        }

        mSlots[slot].mFence = mergedFence;

    } else if (incomingStatus == Fence::Status::Unsignaled) {

        // If one fence has signaled and the other hasn't, the unsignaled

        // fence will approximately correspond with the correct timestamp.

        // There's a small race if both fences signal at about the same time

        // and their statuses are retrieved with unfortunate timing. However,

        // by this point, they will have both signaled and only the timestamp

        // will be slightly off; any dependencies after this point will

        // already have been met.

        mSlots[slot].mFence = fence;

    }

    // else if (currentStatus == Fence::Status::Unsignaled) is a no-op.

    return OK;

}