文件系统事件监听

文件系统事件和网络IO事件一样，也可以通过epoll或者IOCP 事件管理器统一调度，当所监控的文件或文件夹发生了增删改的事件时，就会触发事件回调，进行事件处理。很常见的应用，如配置文件立即生效功能，就可以通过这种方式触发软件内部进行配置更新。也可以用来监控日志文件的更新，拉取最新日志(类似notepad++打开日志文件，如果日志文件更新了，就会提示reload)。

下面分别给出了linux和windows系统下文件系统事件监听的示意代码，仅供参考。

//file: FileMonitor.h#ifndef INOTIFY_FILEMONITOR_H
#define INOTIFY_FILEMONITOR_H#include <string>
#include <map>/*** 文件监视器。* 用于监控文件系统中文件相关的事件，如创建、删除等操作。*/
class FileMonitor {public:FileMonitor() = default;~FileMonitor() = default;void startWatch(const std::string &path);void stopWatch();bool addWatch(const std::string &path);private:// inotify 句柄int inotify_fd{0};// inotify_add_watch返回值 -> 要监控的文件名 的映射std::map<int, std::string> watchDesc2Name;// 是否停止监控bool isStopped{false};
};#endif //INOTIFY_FILEMONITOR_H// file: FileMonitor.cpp#include <sys/inotify.h>
#include <sys/epoll.h>
#include <unistd.h>
#include <thread>
#include <chrono>
#include <cstdio>
#include <iostream>
#include "FileMonitor.h"#define log(format, ...) { \auto now = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());   \char buf[64];                                                                        \strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", std::localtime(&now));               \printf("%s | %llu | ", buf, std::this_thread::get_id());                             \printf(format, ##__VA_ARGS__);                                                       \printf("\n"); }#define EVENT_SIZE  ( sizeof (struct inotify_event) )
#define BUF_LEN     ( 1024 * ( EVENT_SIZE + 16 ) )void FileMonitor::startWatch(const std::string &path) {log("Ready to watch...");// inotify 初始化inotify_fd = inotify_init();if (!addWatch(path)) {return;}// 创建一个 epoll 句柄log("epoll_create");int epfd = epoll_create(256);struct epoll_event ev;ev.data.fd = inotify_fd;        // 设置要处理的事件相关的文件描述符ev.events = EPOLLIN | EPOLLET;  // 设置要处理的事件类型// 注册 epoll 事件log("epoll_ctl");epoll_ctl(epfd, EPOLL_CTL_ADD, inotify_fd, &ev);// 循环监听事件char buffer[BUF_LEN];struct epoll_event events[20];  // 存储从内核得到的事件集合while (!isStopped) {log("epoll_wait...");// 等待事件发生。返回需要处理的事件数目int nfds = epoll_wait(epfd, events, 20, 500);log("Event count: %d", nfds);for (int i = 0; i < nfds; ++i) {/*** epoll_wait 会一直阻塞直到下面2种情况：*   1. 一个文件描述符触发了事件。*   2. 被一个信号处理函数打断，或者 timeout 超时。* 所以下面需要对 fd 进行过滤，判断是否是我们需要的 fd 产生了事件*/if (events[i].data.fd != inotify_fd) {log("Other event, fd=%d", events[i].data.fd);continue;}long length = read(inotify_fd, buffer, BUF_LEN);if (length < 0) {perror("Read failed");}log("Read length: %ld", length);int pos = 0;int count = 0;while (pos < length) {struct inotify_event *event = (struct inotify_event *) &buffer[pos];log("[%d]event->len=%u, event->mask=%#X, EVENT_SIZE=%lu", ++count, event->len, event->mask, EVENT_SIZE);if (event->len) {if (event->mask & IN_CREATE) {log("CREATE: %s", event->name);} else if (event->mask & IN_DELETE) {log("DELETE: %s", event->name);} else if (event->mask & IN_MODIFY) {log("MODIFY: %s", event->name);} else if (event->mask & IN_OPEN) {log("OPEN: %s", event->name);} else if (event->mask & IN_CLOSE) {log("CLOSE: %s", event->name);} else {log("Unknown event, mask=%u", event->mask);}}pos += EVENT_SIZE + event->len;}}}log("Stop inotify");for (auto &ele: watchDesc2Name) {inotify_rm_watch(inotify_fd, ele.first);}close(epfd);close(inotify_fd);
}void FileMonitor::stopWatch() {isStopped = true;
}bool FileMonitor::addWatch(const std::string &path) {// TODO 需要对文件（夹）是否存在进行判断// 监听指定目录下的修改、创建、删除事件int wd = inotify_add_watch(inotify_fd, path.c_str(), IN_MODIFY | IN_CREATE | IN_DELETE);
//    int wd = inotify_add_watch(inotify_fd, path.c_str(), IN_ALL_EVENTS);if (wd < 0) {log("inotify_add_watch failed: %s", path.c_str());return false;}log("Add watch: %s", path.c_str());watchDesc2Name[wd] = path;return true;
}// main: main.cpp
#include <iostream>
#include "FileMonitor.h"int main() {std::string dirPath = "/home/nvidia/logs";FileMonitor fileMonitor;fileMonitor.startWatch(dirPath);return 0;
}// https://github.com/BornToDeath/cpp/blob/main/test/case11_inotify/main.cpp

#include <iostream>
#include <map>
#include <windows.h>
#define DIRECTORY_PATH      L"C://TestFolder"#define CONTAINING_RECORD(address, type, field) ((type *)( \(PCHAR)(address) - \(ULONG_PTR)(&((type *)0)->field)))typedef struct directory_info
{HANDLE    hDir;CHAR          szDirName[MAX_PATH];CHAR          szBuffer[4096];DWORD      dwBufLength;OVERLAPPED Overlapped;  // 此处需要定义overlapp结构
}DIRECTORY_INFO, * LPDIRECTORY_INFO;class cFileUpdateChecker
{
public:cFileUpdateChecker(const wchar_t* root) :hThread(NULL), dwThread(0), hComp(NULL), pdir(NULL) { wsprintf(dirPath,L"%s",root); }~cFileUpdateChecker(){if (hComp) {PostQueuedCompletionStatus(hComp, 0, NULL, NULL);CloseHandle(hComp);}if (hThread)        CloseHandle(hThread);if (pdir){CloseHandle(pdir->hDir);HeapFree(GetProcessHeap(), 0, pdir);}for(auto it = opened_files.begin();it!=opened_files.end();it++){if(it->second != NULL)CloseHandle(it->second);}}// 定义IOCP的工作线程static DWORD WINAPI  ThreadFunc(void* p){cFileUpdateChecker* pHost = (cFileUpdateChecker*)p;LPDIRECTORY_INFO lpdir = NULL;DWORD nbytes, errCode;LPOVERLAPPED lpOverlapped = NULL;PFILE_NOTIFY_INFORMATION fni = NULL;ULONG_PTR completion_key;DWORD wait = 1000;while (true){BOOL bRet = GetQueuedCompletionStatus(pHost->hComp, &nbytes, &completion_key, &lpOverlapped, wait);if (FALSE == bRet ){ errCode = GetLastError();if (errCode == WAIT_TIMEOUT){wait = INFINITE;continue;}elsebreak;}if (lpOverlapped == NULL){break;}else{lpdir = CONTAINING_RECORD(lpOverlapped, DIRECTORY_INFO, Overlapped);if (lpdir){fni = (PFILE_NOTIFY_INFORMATION)lpdir->szBuffer;int filename_length =fni->FileNameLength;wchar_t* root_dir = (wchar_t*)lpdir->szDirName;wchar_t* filename = &fni->FileName[0];switch (fni->Action){case FILE_ACTION_ADDED:wprintf(L"The file %s/%s was added to the directory.\r\n", root_dir, filename);break;case FILE_ACTION_REMOVED:wprintf(L"The file  %s/%s  was removed from the directory.\r\n", root_dir, filename);break;case FILE_ACTION_MODIFIED:{wchar_t file_path_buffer[MAX_PATH]={};wsprintf(file_path_buffer,L"%s\\%s",root_dir, filename);wprintf(L"The file %s was modified. This can be a change in the time stamp or attributes.\r\n", file_path_buffer);auto it = pHost->opened_files.find(file_path_buffer);if(it == pHost->opened_files.end()){HANDLE hFile = CreateFile(file_path_buffer,GENERIC_READ,FILE_SHARE_READ|FILE_SHARE_WRITE,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,NULL);if(hFile != NULL){DWORD dwFilePointer = SetFilePointer(hFile,0,NULL,FILE_END);if(dwFilePointer != INVALID_SET_FILE_POINTER)pHost->opened_files[file_path_buffer]=hFile;elseCloseHandle(hFile);}}else{CHAR szReadText[50] = {};DWORD dwRead = 0;//需要注意的是,FILE_ACTION_MODIFIED信号仅表示文件系统中的该文件节点对象的写状态更新了,至于是否完成落盘,还需要看修改文件的进程是否完成了刷盘。由于实时性问题，刷盘动作可能存在一定的滞后,如果每次进入Modify事件都要增量读取更新的文件内容。可以增加30~50ms的延时bRet = ReadFile(it->second,szReadText,32,&dwRead,NULL);if(bRet == FALSE){CloseHandle(it->second);pHost->opened_files.erase(it);}else{printf("Additional file content: %s.\r\n",szReadText);SetFilePointer(it->second,0,NULL,FILE_END);}}}break;case FILE_ACTION_RENAMED_OLD_NAME:{const wchar_t* new_filename = L"";int new_filename_length = 0;if (fni->NextEntryOffset);{PFILE_NOTIFY_INFORMATION new_fni = (PFILE_NOTIFY_INFORMATION)(lpdir->szBuffer + fni->NextEntryOffset);new_filename = &new_fni->FileName[0];new_filename_length = new_fni->FileNameLength;}wprintf(L"The file  %s/%s  was renamed, and this is the new name %s.\r\n", root_dir, filename, new_filename);}break;case FILE_ACTION_RENAMED_NEW_NAME:wprintf(L"The file  %s/%s  was renamed and this is the new name.\r\n", root_dir,  filename);break;default:break;}// re post eventZeroMemory(&(pHost->pdir->Overlapped), sizeof(OVERLAPPED));ZeroMemory(pHost->pdir->szBuffer, 4096);ReadDirectoryChangesW(pHost->pdir->hDir,pHost->pdir->szBuffer,sizeof(pHost->pdir->szBuffer),TRUE,FILE_NOTIFY_CHANGE_FILE_NAME |FILE_NOTIFY_CHANGE_DIR_NAME |FILE_NOTIFY_CHANGE_ATTRIBUTES |FILE_NOTIFY_CHANGE_SIZE |FILE_NOTIFY_CHANGE_LAST_ACCESS |FILE_NOTIFY_CHANGE_CREATION |FILE_NOTIFY_CHANGE_SECURITY |FILE_NOTIFY_CHANGE_LAST_WRITE,&(pHost->pdir->dwBufLength),(OVERLAPPED*)(&(pHost->pdir->Overlapped)),NULL);}}}return 0;}bool StartChecker(){hComp = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);pdir = (LPDIRECTORY_INFO)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(DIRECTORY_INFO));if (NULL == pdir){return false;}pdir->hDir = CreateFile(dirPath,FILE_LIST_DIRECTORY,FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,NULL,OPEN_EXISTING,FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,NULL);if (pdir->hDir == INVALID_HANDLE_VALUE){return false;}// 启动工作线程hThread = CreateThread(NULL, 0, ThreadFunc, this, 0, &dwThread);if (NULL == hThread){return false;}ZeroMemory(&(pdir->Overlapped), sizeof(OVERLAPPED));ZeroMemory(pdir->szBuffer, 4096);ZeroMemory(pdir->szDirName, MAX_PATH);wsprintf((wchar_t*)pdir->szDirName,L"%s", dirPath);// 投递I/O请求到完成端口HANDLE hRet = CreateIoCompletionPort(pdir->hDir, hComp,NULL, 0);if (NULL == hComp){return false;}BOOL bRet = ReadDirectoryChangesW(pdir->hDir,pdir->szBuffer,4096,TRUE,FILE_NOTIFY_CHANGE_FILE_NAME |FILE_NOTIFY_CHANGE_DIR_NAME |FILE_NOTIFY_CHANGE_ATTRIBUTES |FILE_NOTIFY_CHANGE_SIZE |FILE_NOTIFY_CHANGE_LAST_ACCESS |FILE_NOTIFY_CHANGE_CREATION |FILE_NOTIFY_CHANGE_SECURITY |FILE_NOTIFY_CHANGE_LAST_WRITE,&pdir->dwBufLength,&(pdir->Overlapped),NULL);if (FALSE == bRet){return false;}return true;}
private:HANDLE hThread;DWORD dwThread;HANDLE  hComp;LPDIRECTORY_INFO pdir;WCHAR dirPath[MAX_PATH];std::map<std::wstring,HANDLE> opened_files;
};int main()
{cFileUpdateChecker* ckr = new cFileUpdateChecker(DIRECTORY_PATH);std::cout << "Supervise "; std::wcout << DIRECTORY_PATH << " Begin..." << std::endl;ckr->StartChecker();getchar();delete ckr;getchar();
}// https://blog.csdn.net/nhn_devlab/article/details/6034055