Function RandAddSeedPerfmon

src/randomenv.cpp:65–102

namespace {

void RandAddSeedPerfmon(CSHA512& hasher)
{
#ifdef WIN32
    // Seed with the entire set of perfmon data

    // This can take up to 2 seconds, so only do it every 10 minutes.
    // Initialize last_perfmon to 0 seconds, we don't skip the first call.
    static std::atomic<std::chrono::seconds> last_perfmon{0s};
    auto last_time = last_perfmon.load();
    auto current_time = GetTime<std::chrono::seconds>();
    if (current_time < last_time + std::chrono::minutes{10}) return;
    last_perfmon = current_time;

    std::vector<unsigned char> vData(250000, 0);
    long ret = 0;
    unsigned long nSize = 0;
    const size_t nMaxSize = 10000000; // Bail out at more than 10MB of performance data
    while (true) {
        nSize = vData.size();
        ret = RegQueryValueExA(HKEY_PERFORMANCE_DATA, "Global", nullptr, nullptr, vData.data(), &nSize);
        if (ret != ERROR_MORE_DATA || vData.size() >= nMaxSize)
            break;
        vData.resize(std::min((vData.size() * 3) / 2, nMaxSize)); // Grow size of buffer exponentially
    }
    RegCloseKey(HKEY_PERFORMANCE_DATA);
    if (ret == ERROR_SUCCESS) {
        hasher.Write(vData.data(), nSize);
        memory_cleanse(vData.data(), nSize);
    } else {
        // Performance data is only a best-effort attempt at improving the
        // situation when the OS randomness (and other sources) aren't
        // adequate. As a result, failure to read it is isn't considered critical,
        // so we don't call RandFailure().
        // TODO: Add logging when the logger is made functional before global
        // constructors have been invoked.
    }
#endif
}

/** Helper to easily feed data into a CSHA512.
 *