alien_worker.cc

/*
 * Copyright (C) 2024-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
 */

#include "utils/alien_worker.hh"
#include <seastar/util/log.hh>

using namespace seastar;

namespace utils {

std::thread alien_worker::spawn(seastar::logger& log, int niceness) {
    sigset_t newset;
    sigset_t oldset;
    sigfillset(&newset);
    auto r = ::pthread_sigmask(SIG_SETMASK, &newset, &oldset);
    assert(r == 0);
    auto thread = std::thread([this, &log, niceness] () noexcept {
        errno = 0;
        int nice_value = nice(niceness);
        if (nice_value == -1 && errno != 0) {
            log.warn("Unable to renice worker thread (system error number {}); the thread will compete with reactor, which can cause latency spikes. Try adding CAP_SYS_NICE", errno);
        }

        while (true) {
            std::unique_lock lk(_mut);
            _cv.wait(lk, [this] { return !_pending.empty() || !_running; });
            if (!_running) {
                return;
            }
            auto f = std::move(_pending.front());
            _pending.pop();
            lk.unlock();
            f();
        }
    });
    r = ::pthread_sigmask(SIG_SETMASK, &oldset, nullptr);
    assert(r == 0);
    return thread;
}

alien_worker::alien_worker(seastar::logger& log, int niceness)
    : _thread(spawn(log, niceness))
{}

alien_worker::~alien_worker() {
    {
        std::unique_lock lk(_mut);
        _running = false;
    }
    _cv.notify_one();
    _thread.join();
}

} // namespace utils