nats_Open and nats_Close can't run simultaneously about nats.c HOT 2 CLOSED

client A      A--------->|
client B            B----------->|
opened?       |<---------------->|
              ^                  ^
              |                  |
              nats_Open          nats_Close

client A      A--------->|
client B                      B----------->|
opened?       |<-------->|    |<---------->|
              ^          ^    ^            ^
              |          |    |            |
              nats_Open  |    nats_Open    |
                         nats_Close        nats_Close

client A      A--------->|
client B                 B----------->|
opened?       |<-------->|<---------->|
              ^          ^
              |          |
              nats_Open  !!race condition!!
                         nats_Close and nats_Open are called concurrently

class Nats {
public:
    Nats() {
        std::lock_guard<std::mutex> lock(m);
        nats_Open(-1);
        ++c;
    }

    ~Nats() {
        std::lock_guard<std::mutex> lock(m);
        if (c == 1) {
            nats_Close();
        }
        --c;
    }

private:
    static int c = 0;
    static std::mutex m;
};