Method SelectServer

src/brpc/policy/weighted_randomized_load_balancer.cpp:120–172

}

int WeightedRandomizedLoadBalancer::SelectServer(const SelectIn& in, SelectOut* out) {
    butil::DoublyBufferedData<Servers>::ScopedPtr s;
    if (_db_servers.Read(&s) != 0) {
        return ENOMEM;
    }
    size_t n = s->server_list.size();
    if (n == 0) {
        return ENODATA;
    }

    butil::FlatSet<SocketId> random_traversed;
    uint64_t weight_sum = s->weight_sum;
    for (size_t i = 0; i < n; ++i) {
        uint64_t random_weight = butil::fast_rand_less_than(weight_sum);
        const Server random_server(0, 0, random_weight);
        const auto& server =
            std::lower_bound(s->server_list.begin(), s->server_list.end(),
                             random_server, server_compare);
        const SocketId id = server->id;
        if (ExcludedServers::IsExcluded(in.excluded, id)) {
            continue;
        }
        random_traversed.insert(id);
        if (IsServerAvailable(id, out->ptr)) {
            // An available server is found.
            return 0;
        }
    }

    if (random_traversed.size() < n) {
        // Try to traverse the remaining servers to find an available server.
        uint32_t offset = butil::fast_rand_less_than(n);
        uint32_t stride = bthread::prime_offset();
        for (size_t i = 0; i < n; ++i) {
            offset = (offset + stride) % n;
            SocketId id = s->server_list[offset].id;
            if (NULL != random_traversed.seek(id)) {
                continue;
            }
            if (IsServerAvailable(id, out->ptr)) {
                if (!ExcludedServers::IsExcluded(in.excluded, id)) {
                    // Prioritize servers that are not excluded.
                    return 0;
                }
            }
        }
    }

    // Returns EHOSTDOWN, if no available server is found
    // after traversing the whole server list.
    // Otherwise, returns 0 with a available excluded server.
    return NULL == out->ptr ? EHOSTDOWN : 0;
}

LoadBalancer* WeightedRandomizedLoadBalancer::New(
    const butil::StringPiece&) const {