Method processThreadLocalChanges

src/Common/ThreadProfileEvents.cpp:355–457

}

bool PerfEventsCounters::processThreadLocalChanges(const std::string & needed_events_list)
{
    const auto valid_event_indices = eventIndicesFromString(needed_events_list);

    // find state changes (if there are any)
    bool old_state[NUMBER_OF_RAW_EVENTS];
    for (size_t i = 0; i < NUMBER_OF_RAW_EVENTS; ++i)
        old_state[i] = thread_events_descriptors_holder.descriptors[i] != -1;

    bool new_state[NUMBER_OF_RAW_EVENTS];
    std::fill_n(new_state, NUMBER_OF_RAW_EVENTS, false);
    for (size_t opened_index : valid_event_indices)
        new_state[opened_index] = true;

    std::vector<size_t> events_to_open;
    std::vector<size_t> events_to_release;
    for (size_t i = 0; i < NUMBER_OF_RAW_EVENTS; ++i)
    {
        bool old_one = old_state[i];
        bool new_one = new_state[i];

        if (old_one == new_one)
        {
            if (old_one
                && !validatePerfEventDescriptor(
                    thread_events_descriptors_holder.descriptors[i]))
            {
                events_to_open.push_back(i);
            }
            continue;
        }

        if (new_one)
            events_to_open.push_back(i);
        else
            events_to_release.push_back(i);
    }

    // release unused descriptors
    for (size_t i : events_to_release)
    {
        int & fd = thread_events_descriptors_holder.descriptors[i];
        disablePerfEvent(fd);
        releasePerfEvent(fd);
        fd = -1;
    }

    if (events_to_open.empty())
    {
        return true;
    }

    // check permissions
    // cat /proc/sys/kernel/perf_event_paranoid
    // -1: Allow use of (almost) all events by all users
    // >=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
    // >=1: Disallow CPU event access by users without CAP_SYS_ADMIN
    // >=2: Disallow kernel profiling by users without CAP_SYS_ADMIN