Method ProcessTracer

src/pystack/_pystack/process.cpp:136–191

}

ProcessTracer::ProcessTracer(pid_t pid)
{
    std::unordered_map<int, int> error_by_tid;

    bool found_new_tid = true;
    while (found_new_tid) {
        found_new_tid = false;

        auto tids = getProcessTids(pid);
        for (auto& tid : tids) {
            if (d_tids.count(tid)) {
                continue;  // already stopped
            }

            auto err_it = error_by_tid.find(tid);
            if (err_it != error_by_tid.end()) {
                // We got an error for this TID on the last iteration.
                // Since we found the TID again this iteration, it still
                // belongs to us and should have been stoppable.
                detachFromProcess();

                int error = err_it->second;
                if (error == EPERM) {
                    throw std::runtime_error(PERM_MESSAGE);
                }
                throw std::system_error(error, std::generic_category());
            }

            found_new_tid = true;

            LOG(INFO) << "Trying to stop thread " << tid;
            long ret = ptrace(PTRACE_ATTACH, tid, nullptr, nullptr);
            if (ret < 0) {
                int error = errno;
                LOG(WARNING) << "Failed to attach to thread " << tid << ": " << strerror(error);
                error_by_tid.emplace(tid, error);
                continue;
            }

            // Add each tid as we attach: these are the tids we detach from.
            d_tids.insert(tid);

            LOG(INFO) << "Waiting for thread " << tid << " to be stopped";
            ret = waitpid(tid, nullptr, WUNTRACED);
            if (ret < 0) {
                // In some old kernels is not possible to use WUNTRACED with
                // threads (only the main thread will return a non zero value).
                if (tid == pid || errno != ECHILD) {
                    detachFromProcess();
                }
            }
            LOG(INFO) << "Thread " << tid << " stopped";
        }
    }
    LOG(INFO) << "All " << d_tids.size() << " threads stopped";
}

void