C++ 写一个多线程，可以配置输出等级的日志类

以下是一个基本的多线程日志类，可以配置输出等级：

#include <iostream>
#include <fstream>
#include <ctime>
#include <mutex>
#include <thread>
#include <queue>
#include <condition_variable>

using namespace std;

enum class LogLevel {
    DEBUG,
    INFO,
    WARNING,
    ERROR
};

class Logger {
public:
    Logger(LogLevel level = LogLevel::DEBUG) : m_logLevel(level), m_stop(false) {
        m_thread = thread(&Logger::worker, this);
    }

    ~Logger() {
        m_stop = true;
        m_cv.notify_one();
        m_thread.join();
    }

    void log(LogLevel level, const string& message) {
        unique_lock<mutex> lock(m_mutex);
        if (level < m_logLevel) {
            return;
        }
        m_queue.push(make_pair(level, message));
        m_cv.notify_one();
    }

    void setLogLevel(LogLevel level) {
        m_logLevel = level;
    }

private:
    void worker() {
        ofstream file("log.txt");
        if (!file.is_open()) {
            cerr << "Failed to open log file!" << endl;
            return;
        }
        while (!m_stop) {
            unique_lock<mutex> lock(m_mutex);
            m_cv.wait(lock, [this] { return !m_queue.empty() || m_stop; });
            while (!m_queue.empty()) {
                auto log = m_queue.front();
                m_queue.pop();
                lock.unlock();
                file << getTimestamp() << " [" << getLevelString(log.first) << "] " << log.second << endl;
                lock.lock();
            }
        }
        file.close();
    }

    string getTimestamp() {
        time_t now = time(nullptr);
        char buffer[20];
        strftime(buffer, sizeof(buffer), "%Y-%m-%d %H:%M:%S", localtime(&now));
        return buffer;
    }

    string getLevelString(LogLevel level) {
        switch (level) {
        case LogLevel::DEBUG:
            return "DEBUG";
        case LogLevel::INFO:
            return "INFO";
        case LogLevel::WARNING:
            return "WARNING";
        case LogLevel::ERROR:
            return "ERROR";
        default:
            return "";
        }
    }

    LogLevel m_logLevel;
    queue<pair<LogLevel, string>> m_queue;
    mutex m_mutex;
    condition_variable m_cv;
    thread m_thread;
    bool m_stop;
};

int main() {
    Logger logger(LogLevel::INFO);
    logger.log(LogLevel::DEBUG, "Debug message"); // shouldn't be printed
    logger.log(LogLevel::INFO, "Info message"); // should be printed
    logger.log(LogLevel::WARNING, "Warning message"); // should be printed
    logger.log(LogLevel::ERROR, "Error message"); // should be printed
    logger.setLogLevel(LogLevel::WARNING);
    logger.log(LogLevel::DEBUG, "Debug message"); // shouldn't be printed
    logger.log(LogLevel::INFO, "Info message"); // shouldn't be printed
    logger.log(LogLevel::WARNING, "Warning message"); // should be printed
    logger.log(LogLevel::ERROR, "Error message"); // should be printed
    return 0;
}

该日志类使用一个队列来缓存日志信息，当队列中有日志时，工作线程会将其写入文件。日志的输出等级可以通过设置 `LogLevel` 来控制，低于该等级的日志将被忽略。同时，在程序结束前，需要调用 `Logger` 的析构函数来结束工作线程。