Qt原始碼解析-QFileSystemWatcher原始碼剖析(Linux).md
公眾號:Qt那些事兒
簡介
QFileSystemWatcher的作用是監視本地資料夾的變化以及檔案的變化。
概述
QFileSystemWatcher的實現類是QFileSystemWatcherPrivate。 其中QFileSystemWatcherPrivate中的關鍵成員變數QFileSystemWatcherEngine用於監視目錄以及檔案的變化,傳送訊號給QFileystemWatcher。其中QFileSystemWatcherEngine派生了三個類。
class QFileSystemWatcherEngine : public QThread
其派生的子類三種類型分別為
// 這個用於監控Dir的變化
class QDnotifyFileSystemWatcherEngine : public QFileSystemWatcherEngine
// 這個外部沒有暴露對應的變化介面,但是檢測其它型別的目錄變化時我們會用到
class QPollingFileSystemWatcherEngine : public QFileSystemWatcherEngine
// 這個用於檢測檔案型別的變化
class QInotifyFileSystemWatcherEngine : public QFileSystemWatcherEngine
QInotifyFileSystemWatcherEngine
QInotifyFileSystemWatcherEngine用於監視檔案的變化。
// 太長可以忽略,這是詳細實現
//media/zhangpf/workspace1/Qt4.8.7/qt-everywhere-opensource-src-4.8.7/src/corelib/io/qfilesystemwatcher_inotify_p.h #include "qfilesystemwatcher_p.h" #ifndef QT_NO_FILESYSTEMWATCHER #include <qhash.h> #include <qmutex.h> QT_BEGIN_NAMESPACE class QInotifyFileSystemWatcherEngine : public QFileSystemWatcherEngine { Q_OBJECT public: ~QInotifyFileSystemWatcherEngine(); static QInotifyFileSystemWatcherEngine *create(); //單例模式 void run(); QStringList addPaths(const QStringList &paths, QStringList *files, QStringList *directories); QStringList removePaths(const QStringList &paths, QStringList *files, QStringList *directories); void stop(); private Q_SLOTS: void readFromInotify(); private: QInotifyFileSystemWatcherEngine(int fd); int inotifyFd; QMutex mutex; QHash<QString, int> pathToID; QHash<int, QString> idToPath; }; QT_END_NAMESPACE #endif // QT_NO_FILESYSTEMWATCHER #endif // QFILESYSTEMWATCHER_INOTIFY_P_H // cpp #include <sys/inotify.h> #endif QT_BEGIN_NAMESPACE QInotifyFileSystemWatcherEngine *QInotifyFileSystemWatcherEngine::create() { int fd = -1; #ifdef IN_CLOEXEC fd = inotify_init1(IN_CLOEXEC); #endif if (fd == -1) { fd = inotify_init(); if (fd == -1) return 0; ::fcntl(fd, F_SETFD, FD_CLOEXEC); } return new QInotifyFileSystemWatcherEngine(fd); } QInotifyFileSystemWatcherEngine::QInotifyFileSystemWatcherEngine(int fd) : inotifyFd(fd) { fcntl(inotifyFd, F_SETFD, FD_CLOEXEC); moveToThread(this); } QInotifyFileSystemWatcherEngine::~QInotifyFileSystemWatcherEngine() { foreach (int id, pathToID) inotify_rm_watch(inotifyFd, id < 0 ? -id : id); ::close(inotifyFd); } void QInotifyFileSystemWatcherEngine::run() { QSocketNotifier sn(inotifyFd, QSocketNotifier::Read, this); //通過socket來監視檔案的變化,替代thread一個很好的方式 connect(&sn, SIGNAL(activated(int)), SLOT(readFromInotify())); (void) exec(); } QStringList QInotifyFileSystemWatcherEngine::addPaths(const QStringList &paths, QStringList *files, QStringList *directories) { QMutexLocker locker(&mutex); QStringList p = paths; QMutableListIterator<QString> it(p); while (it.hasNext()) { QString path = it.next(); QFileInfo fi(path); bool isDir = fi.isDir(); if (isDir) { if (directories->contains(path)) continue; } else { if (files->contains(path)) continue; } int wd = inotify_add_watch(inotifyFd, QFile::encodeName(path), (isDir ? (0 | IN_ATTRIB | IN_MOVE | IN_CREATE | IN_DELETE | IN_DELETE_SELF ) : (0 | IN_ATTRIB | IN_MODIFY | IN_MOVE | IN_MOVE_SELF | IN_DELETE_SELF ))); if (wd <= 0) { perror("QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed"); continue; } it.remove(); int id = isDir ? -wd : wd; if (id < 0) { directories->append(path); } else { files->append(path); } pathToID.insert(path, id); idToPath.insert(id, path); } start(); return p; } QStringList QInotifyFileSystemWatcherEngine::removePaths(const QStringList &paths, QStringList *files, QStringList *directories) { QMutexLocker locker(&mutex); QStringList p = paths; QMutableListIterator<QString> it(p); while (it.hasNext()) { QString path = it.next(); int id = pathToID.take(path); QString x = idToPath.take(id); if (x.isEmpty() || x != path) continue; int wd = id < 0 ? -id : id; // qDebug() << "removing watch for path" << path << "wd" << wd; inotify_rm_watch(inotifyFd, wd); it.remove(); if (id < 0) { directories->removeAll(path); } else { files->removeAll(path); } } return p; } void QInotifyFileSystemWatcherEngine::stop() { quit(); } void QInotifyFileSystemWatcherEngine::readFromInotify() { //主要是通過unix庫函式來獲取檔案對應的詳細資訊。再跟addpath實現中快取下來的資訊做對比,來檢測檔案的變化。 QMutexLocker locker(&mutex); // qDebug() << "QInotifyFileSystemWatcherEngine::readFromInotify"; int buffSize = 0; ioctl(inotifyFd, FIONREAD, (char *) &buffSize); QVarLengthArray<char, 4096> buffer(buffSize); buffSize = read(inotifyFd, buffer.data(), buffSize); char *at = buffer.data(); char * const end = at + buffSize; QHash<int, inotify_event *> eventForId; while (at < end) { inotify_event *event = reinterpret_cast<inotify_event *>(at); if (eventForId.contains(event->wd)) eventForId[event->wd]->mask |= event->mask; else eventForId.insert(event->wd, event); at += sizeof(inotify_event) + event->len; } QHash<int, inotify_event *>::const_iterator it = eventForId.constBegin(); while (it != eventForId.constEnd()) { const inotify_event &event = **it; ++it; // qDebug() << "inotify event, wd" << event.wd << "mask" << hex << event.mask; int id = event.wd; QString path = idToPath.value(id); if (path.isEmpty()) { // perhaps a directory? id = -id; path = idToPath.value(id); if (path.isEmpty()) continue; } // qDebug() << "event for path" << path; if ((event.mask & (IN_DELETE_SELF | IN_MOVE_SELF | IN_UNMOUNT)) != 0) { pathToID.remove(path); idToPath.remove(id); inotify_rm_watch(inotifyFd, event.wd); if (id < 0) emit directoryChanged(path, true); else emit fileChanged(path, true); } else { if (id < 0) emit directoryChanged(path, false); else emit fileChanged(path, false); } } } QT_END_NAMESPACE #endif // QT_NO_FILESYSTEMWATCHER
這是一個單例模式,裡邊的核心程式碼其實就是講的是Inotify相關的函式。其中的關鍵的點,我已經打上備註。這個類中的主要實現是Linux下的Inotify的使用相關。
Inotify
Inotify簡單的來講是在Linux下監視檔案與資料夾的相關機制,本來想自己寫這一部分教程的,可是有一篇文章寫的太好了,忍不住給大家分享了。
https://www.ibm.com/developerworks/cn/linux/l-inotify/ 看完這一篇文章之後我覺得你對Linux下如何監視檔案應該有了解了,甚至可以自己封裝一個類給大家用。
資料夾的檢測變化實現類 QDnotifyFileSystemWatcherEngine
class QDnotifyFileSystemWatcherEngine : public QFileSystemWatcherEngine
{
Q_OBJECT
public:
virtual ~QDnotifyFileSystemWatcherEngine();
static QDnotifyFileSystemWatcherEngine *create();
void run();
QStringList addPaths(const QStringList &paths, QStringList *files, QStringList *directories);
QStringList removePaths(const QStringList &paths, QStringList *files, QStringList *directories);
void stop();
private Q_SLOTS:
void refresh(int);
private:
//這個結構體比較關鍵
struct Directory {
Directory() : fd(0), parentFd(0), isMonitored(false) {}
Directory(const Directory &o) : path(o.path),
fd(o.fd),
parentFd(o.parentFd),
isMonitored(o.isMonitored),
files(o.files) {}
QString path;
int fd;
int parentFd;
bool isMonitored;
//這個結構體也比較關鍵
struct File {
File() : ownerId(0u), groupId(0u), permissions(0u) { }
File(const File &o) : path(o.path),
ownerId(o.ownerId),
groupId(o.groupId),
permissions(o.permissions),
lastWrite(o.lastWrite) {}
QString path;
bool updateInfo();
uint ownerId;
uint groupId;
QFile::Permissions permissions;
QDateTime lastWrite;
};
QList<File> files;
};
QDnotifyFileSystemWatcherEngine();
QMutex mutex;
QHash<QString, int> pathToFD;
QHash<int, Directory> fdToDirectory;
QHash<int, int> parentToFD;
};
//cpp
QDnotifySignalThread::QDnotifySignalThread()
: isExecing(false)
{
moveToThread(this);
qt_safe_pipe(qfswd_fileChanged_pipe, O_NONBLOCK);
struct sigaction oldAction;
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_sigaction = qfswd_sigio_monitor;
action.sa_flags = SA_SIGINFO;
::sigaction(SIGIO, &action, &oldAction);
if (!(oldAction.sa_flags & SA_SIGINFO))
qfswd_old_sigio_handler = oldAction.sa_handler;
else
qfswd_old_sigio_action = oldAction.sa_sigaction;
}
QDnotifySignalThread::~QDnotifySignalThread()
{
if(isRunning()) {
quit();
QThread::wait();
}
}
bool QDnotifySignalThread::event(QEvent *e)
{
if(e->type() == QEvent::User) {
QMutexLocker locker(&mutex);
isExecing = true;
wait.wakeAll();
return true;
} else {
return QThread::event(e);
}
}
void QDnotifySignalThread::startNotify()
{
// Note: All this fancy waiting for the thread to enter its event
// loop is to avoid nasty messages at app shutdown when the
// QDnotifySignalThread singleton is deleted
start();
mutex.lock();
while(!isExecing)
wait.wait(&mutex);
mutex.unlock();
}
void QDnotifySignalThread::run()
{
QSocketNotifier sn(qfswd_fileChanged_pipe[0], QSocketNotifier::Read, this);
connect(&sn, SIGNAL(activated(int)), SLOT(readFromDnotify()));
QCoreApplication::instance()->postEvent(this, new QEvent(QEvent::User));
(void) exec();
}
void QDnotifySignalThread::readFromDnotify()
{
int fd;
int readrv = qt_safe_read(qfswd_fileChanged_pipe[0], reinterpret_cast<char*>(&fd), sizeof(int));
// Only expect EAGAIN or EINTR. Other errors are assumed to be impossible.
if(readrv != -1) {
Q_ASSERT(readrv == sizeof(int));
Q_UNUSED(readrv);
if(0 == fd)
quit();
else
emit fdChanged(fd);
}
}
QDnotifyFileSystemWatcherEngine::QDnotifyFileSystemWatcherEngine()
{
QObject::connect(dnotifySignal(), SIGNAL(fdChanged(int)),
this, SLOT(refresh(int)), Qt::DirectConnection);
}
QDnotifyFileSystemWatcherEngine::~QDnotifyFileSystemWatcherEngine()
{
QMutexLocker locker(&mutex);
for(QHash<int, Directory>::ConstIterator iter = fdToDirectory.constBegin();
iter != fdToDirectory.constEnd();
++iter) {
qt_safe_close(iter->fd);
if(iter->parentFd)
qt_safe_close(iter->parentFd);
}
}
QDnotifyFileSystemWatcherEngine *QDnotifyFileSystemWatcherEngine::create()
{
return new QDnotifyFileSystemWatcherEngine();
}
void QDnotifyFileSystemWatcherEngine::run()
{
qFatal("QDnotifyFileSystemWatcherEngine thread should not be run");
}
QStringList QDnotifyFileSystemWatcherEngine::addPaths(const QStringList &paths, QStringList *files, QStringList *directories)
{
QMutexLocker locker(&mutex);
QStringList p = paths;
QMutableListIterator<QString> it(p);
while (it.hasNext()) {
QString path = it.next();
QFileInfo fi(path);
if(!fi.exists()) {
continue;
}
bool isDir = fi.isDir();
if (isDir && directories->contains(path)) {
continue; // Skip monitored directories
} else if(!isDir && files->contains(path)) {
continue; // Skip monitored files
}
if(!isDir)
path = fi.canonicalPath();
// Locate the directory entry (creating if needed)
int fd = pathToFD[path];
if(fd == 0) {
QT_DIR *d = QT_OPENDIR(path.toUtf8().constData());
if(!d) continue; // Could not open directory
QT_DIR *parent = 0;
QDir parentDir(path);
if(!parentDir.isRoot()) {
parentDir.cdUp();
parent = QT_OPENDIR(parentDir.path().toUtf8().constData());
if(!parent) {
QT_CLOSEDIR(d);
continue;
}
}
fd = qt_safe_dup(::dirfd(d));
int parentFd = parent ? qt_safe_dup(::dirfd(parent)) : 0;
QT_CLOSEDIR(d);
if(parent) QT_CLOSEDIR(parent);
Q_ASSERT(fd);
if(::fcntl(fd, F_SETSIG, SIGIO) ||
::fcntl(fd, F_NOTIFY, DN_MODIFY | DN_CREATE | DN_DELETE |
DN_RENAME | DN_ATTRIB | DN_MULTISHOT) ||
(parent && ::fcntl(parentFd, F_SETSIG, SIGIO)) ||
(parent && ::fcntl(parentFd, F_NOTIFY, DN_DELETE | DN_RENAME |
DN_MULTISHOT))) {
continue; // Could not set appropriate flags
}
Directory dir;
dir.path = path;
dir.fd = fd;
dir.parentFd = parentFd;
fdToDirectory.insert(fd, dir);
pathToFD.insert(path, fd);
if(parentFd)
parentToFD.insert(parentFd, fd);
}
Directory &directory = fdToDirectory[fd];
if(isDir) {
directory.isMonitored = true;
} else {
Directory::File file;
file.path = fi.filePath();
file.lastWrite = fi.lastModified();
directory.files.append(file);
pathToFD.insert(fi.filePath(), fd);
}
it.remove();
if(isDir) {
directories->append(path);
} else {
files->append(fi.filePath());
}
}
dnotifySignal()->startNotify();
return p;
}
QStringList QDnotifyFileSystemWatcherEngine::removePaths(const QStringList &paths, QStringList *files, QStringList *directories)
{
QMutexLocker locker(&mutex);
QStringList p = paths;
QMutableListIterator<QString> it(p);
while (it.hasNext()) {
QString path = it.next();
int fd = pathToFD.take(path);
if(!fd)
continue;
Directory &directory = fdToDirectory[fd];
bool isDir = false;
if(directory.path == path) {
isDir = true;
directory.isMonitored = false;
} else {
for(int ii = 0; ii < directory.files.count(); ++ii) {
if(directory.files.at(ii).path == path) {
directory.files.removeAt(ii);
break;
}
}
}
if(!directory.isMonitored && directory.files.isEmpty()) {
// No longer needed
qt_safe_close(directory.fd);
pathToFD.remove(directory.path);
fdToDirectory.remove(fd);
}
if(isDir) {
directories->removeAll(path);
} else {
files->removeAll(path);
}
it.remove();
}
return p;
}
void QDnotifyFileSystemWatcherEngine::refresh(int fd)
{
QMutexLocker locker(&mutex);
bool wasParent = false;
QHash<int, Directory>::Iterator iter = fdToDirectory.find(fd);
if(iter == fdToDirectory.end()) {
QHash<int, int>::Iterator pIter = parentToFD.find(fd);
if(pIter == parentToFD.end())
return;
iter = fdToDirectory.find(*pIter);
if (iter == fdToDirectory.end())
return;
wasParent = true;
}
Directory &directory = *iter;
if(!wasParent) {
for(int ii = 0; ii < directory.files.count(); ++ii) {
Directory::File &file = directory.files[ii];
if(file.updateInfo()) {
// Emit signal
QString filePath = file.path;
bool removed = !QFileInfo(filePath).exists();
if(removed) {
directory.files.removeAt(ii);
--ii;
}
emit fileChanged(filePath, removed);
}
}
}
if(directory.isMonitored) {
// Emit signal
bool removed = !QFileInfo(directory.path).exists();
QString path = directory.path;
if(removed)
directory.isMonitored = false;
emit directoryChanged(path, removed);
}
if(!directory.isMonitored && directory.files.isEmpty()) {
qt_safe_close(directory.fd);
if(directory.parentFd) {
qt_safe_close(directory.parentFd);
parentToFD.remove(directory.parentFd);
}
fdToDirectory.erase(iter);
}
}
void QDnotifyFileSystemWatcherEngine::stop()
{
}
bool QDnotifyFileSystemWatcherEngine::Directory::File::updateInfo()
{
QFileInfo fi(path);
QDateTime nLastWrite = fi.lastModified();
uint nOwnerId = fi.ownerId();
uint nGroupId = fi.groupId();
QFile::Permissions nPermissions = fi.permissions();
if(nLastWrite != lastWrite ||
nOwnerId != ownerId ||
nGroupId != groupId ||
nPermissions != permissions) {
ownerId = nOwnerId;
groupId = nGroupId;
permissions = nPermissions;
lastWrite = nLastWrite;
return true;
} else {
return false;
}
}
Dnotify
Dnotify同理,也是使用的Linux的系統函式 /usr/include/unistd.h 主要是這個標頭檔案中的函式。有一些關於檔案描述符相關的函式
裡邊主要監控的是其內部類的相關的資訊
struct Directory {
Directory() : fd(0), parentFd(0), isMonitored(false) {}
Directory(const Directory &o) : path(o.path),
fd(o.fd),
parentFd(o.parentFd),
isMonitored(o.isMonitored),
files(o.files) {}
QString path;
int fd;
int parentFd;
bool isMonitored;
struct File {
File() : ownerId(0u), groupId(0u), permissions(0u) { }
File(const File &o) : path(o.path),
ownerId(o.ownerId),
groupId(o.groupId),
permissions(o.permissions),
lastWrite(o.lastWrite) {}
QString path;
bool updateInfo();
uint ownerId;
uint groupId;
QFile::Permissions permissions;
QDateTime lastWrite;
可以直接看這個結構D需要這四個描述資訊
QString path; //路徑
int fd; //檔案的描述符
int parentFd; //父親的描述符號
bool isMonitored; //是否正在監控
其中這四個資訊都是通過Linux的庫函式與結構體來獲取的。 其中遍歷資料夾則是使用Qt的QFileInfo來遍歷新增paths的資訊,儲存到其類的成員變數中。
// Directory iteration
#define QT_DIR DIR
#define QT_OPENDIR ::opendir
#define QT_CLOSEDIR ::closedir
Dir下的file需要這些資訊
QString path;
uint ownerId;
uint groupId;
QFile::Permissions permissions;
QDateTime lastWrite;
現在說一下關鍵程式碼
ret = ::pipe(pipefd);
if (ret == -1)
return -1;
::fcntl(pipefd[0], F_SETFD, FD_CLOEXEC);
::fcntl(pipefd[1], F_SETFD, FD_CLOEXEC);
// set non-block too?
if (flags & O_NONBLOCK) {
::fcntl(pipefd[0], F_SETFL, ::fcntl(pipefd[0], F_GETFL) | O_NONBLOCK);
::fcntl(pipefd[1], F_SETFL, ::fcntl(pipefd[1], F_GETFL) | O_NONBLOCK);
}
其中 pipefd[0]表示讀,pipefd[1]表示寫,實際上
關鍵程式碼在這裡。
void QDnotifySignalThread::run()
{
QSocketNotifier sn(qfswd_fileChanged_pipe[0], QSocketNotifier::Read, this);
connect(&sn, SIGNAL(activated(int)), SLOT(readFromDnotify()));
QCoreApplication::instance()->postEvent(this, new QEvent(QEvent::User));
(void) exec();
}
這段程式碼實際上是使用QSocketNotifier實時檢測出從pip管道中讀取有關於檔案資訊的變化,加到了Qt在Linux下的事件迴圈中(還記上以前有個老哥寫的那個u盤檢測工具麼?實際上原理跟這個一樣,都是通過socket來讀取檔案描述符的狀態來檢測其變化)。然後等待其訊息通知變化。這樣來實時監控資料夾與檔案的變化。其中QDnotify大量使用了Unix的庫函式,建議有興趣的可以多讀讀Unix高階環境程式設計這本書,可以當個字典來看。我也不一個個解釋了。實際上這個類,我讀起來也是有點吃力,因為大部分都是Linux的庫函式,還是得補補課去看看《Unix環境高階程式設計》了
總結
這兩個類的主要原理是先快取當前addpath的檔案or資料夾的資訊,然後再通過socket來實時檢測其變化。獲取當前的資訊與快取的資訊做對比,如果有變化,就傳送對應的訊號。這樣我們就可以檢測到檔案or資料夾的變化了。
公眾號:Qt那些事兒