inotify 配置重载

Inotify Config Reload

专题: Systems & Architecture / 系统与架构
难度: L2
来源: MyntBit

个人笔记

题目详情

高频交易系统需要动态风险管理，日内调整持仓限制和订单大小而不承担系统重启的延迟。配置文件热重载允许交易引擎原子更新风控参数。

任务：实现 ConfigWatcher 类，使用 inotify 监控配置文件变更。文件修改时读取新配置、校验合法性、原子替换当前配置。支持多个配置文件同时监控。

英文原题

High-frequency trading systems require dynamic risk management to adjust position limits and order sizes intra-day without incurring the latency of a system restart. Hot-reloading configuration files allows trading engines to atomically update risk parameters in response to market volatility or strategy performance. This mechanism ensures continuous operation while maintaining strict compliance with evolving risk constraints.
Task
Implement a RiskEngine class that manages dynamic risk limits th

解析

问题分析

inotify 监控文件系统事件（修改、删除、创建）。当配置文件变更时，应用接收 IN_MODIFY 事件并自动热加载配置，无需手动重启。

实现

class ConfigWatcher {
    int fd_, wd_;
public:
    ConfigWatcher(const char* path) {
        fd_ = ::inotify_init1(IN_NONBLOCK);
        wd_ = ::inotify_add_watch(fd_, path, IN_MODIFY | IN_CLOSE_WRITE);
    }
    bool changed() {
        char buf[4096];
        ssize_t n = ::read(fd_, buf, sizeof(buf));
        if (n <= 0) return false;
        for (char* p = buf; p < buf + n; ) {
            auto* ev = (inotify_event*)p;
            if (ev->mask & (IN_MODIFY | IN_CLOSE_WRITE)) return true;
            p += sizeof(inotify_event) + ev->len;
        }
        return false;
    }
    ~ConfigWatcher() { ::inotify_rm_watch(fd_, wd_); ::close(fd_); }
};

复杂度与边界

时间复杂度：changed O(事件数)
空间复杂度：O(1)
边界条件：(1) 编辑器保存可能触发多次事件（需防抖）(2) 符号链接变化需单独监控 (3) inotify 队列满会丢失事件

英文解析

Analysis

inotify monitors filesystem events (modify, delete, create). When a configuration file changes, the application receives IN_MODIFY events and automatically hot-reloads the configuration without manual restart.

Solution

class ConfigWatcher {
    int fd_, wd_;
public:
    ConfigWatcher(const char* path) {
        fd_ = ::inotify_init1(IN_NONBLOCK);
        wd_ = ::inotify_add_watch(fd_, path, IN_MODIFY | IN_CLOSE_WRITE);
    }
    bool changed() {
        char buf[4096];
        ssize_t n = ::read(fd_, buf, sizeof(buf));
        if (n <= 0) return false;
        for (char* p = buf; p < buf + n; ) {
            auto* ev = (inotify_event*)p;
            if (ev->mask & (IN_MODIFY | IN_CLOSE_WRITE)) return true;
            p += sizeof(inotify_event) + ev->len;
        }
        return false;
    }
    ~ConfigWatcher() { ::inotify_rm_watch(fd_, wd_); ::close(fd_); }
};

Complexity & Edge Cases

Time complexity: changed O(event count)
Space complexity: O(1)
Edge cases: (1) Editor saves may trigger multiple events (need debounce) (2) Symlink changes require separate monitoring (3) inotify queue overflow drops events

Verification

Modify watched config file, verify changed() returns true. Test debounce logic for multiple rapid saves. Confirm inotify overflow detection.

Key Considerations

Hot-reload via inotify eliminates restart downtime for configuration changes. In production trading systems, risk limits and trading parameters change during the day - inotify-based reload applies new limits within milliseconds without interrupting order flow.