```
bitcoind -par=1
```

Excerpt from the `debug.log`:

```
Using 0 threads for script verification
```

Zero? I guess not ;)
{
    if (initialSync || !pBlockIndex)
        return;
    std::string strCmd = gArgs.GetArg("-blocknotify", "");
    if (!strCmd.empty()) {
        boost::replace_all(strCmd, "%s", pBlockIndex->GetBlockHash().GetHex());
        std::thread t(runCommand, strCmd);
        t.detach(); 
    }
}
#endif
static bool fHaveGenesis = false;
static Mutex g_genesis_wait_mutex;
static std::condition_variable g_genesis_wait_cv;
static void BlockNotifyGenesisWait(bool, const CBlockIndex *pBlockIndex)
{
    if (pBlockIndex != nullptr) {
        {
            LOCK(g_genesis_wait_mutex);
            fHaveGenesis = true;
        }
        g_genesis_wait_cv.notify_all();
    }
}
struct CImportingNow
{
    CImportingNow() {