status_t BufferStateLayer::addReleaseFence(const sp<CallbackHandle>& ch,
                                           const sp<Fence>& fence) {
    if (ch == nullptr) {
        return OK;
    }
    ch->previousReleaseCallbackId = mPreviousReleaseCallbackId;
    if (!ch->previousReleaseFence.get()) {
        ch->previousReleaseFence = fence;
        return OK;
    }

    // Below logic is lifted from ConsumerBase.cpp:
    // Check status of fences first because merging is expensive.
    // Merging an invalid fence with any other fence results in an
    // invalid fence.
    auto currentStatus = ch->previousReleaseFence->getStatus();
    if (currentStatus == Fence::Status::Invalid) {
        ALOGE("Existing fence has invalid state, layer: %s", mName.c_str());
        return BAD_VALUE;
    }

    auto incomingStatus = fence->getStatus();
    if (incomingStatus == Fence::Status::Invalid) {
        ALOGE("New fence has invalid state, layer: %s", mName.c_str());
        ch->previousReleaseFence = fence;
        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", mName.c_str());
        sp<Fence> mergedFence = Fence::merge(
                fenceName, ch->previousReleaseFence, fence);
        if (!mergedFence.get()) {
            ALOGE("failed to merge release fences, layer: %s", mName.c_str());
            // synchronization is broken, the best we can do is hope fences
            // signal in order so the new fence will act like a union
            ch->previousReleaseFence = fence;
            return BAD_VALUE;
        }
        ch->previousReleaseFence = 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.
        ch->previousReleaseFence = fence;
    }
    // else if (currentStatus == Fence::Status::Unsignaled) is a no-op.

    return OK;
}