core/desktopentry: add file system watcher for desktop entry directories #114

bbedward · 2025-07-14T15:13:03Z

DesktopEntries only scans one time~~, and doesnt expose scanning functions to QML. This adds a rescan function, a signal for applications changed. It just allows a nicer launcher that doesn't get stale.~~

This adds:

DesktopUtils which had a common function for locating .desktop files
DesktopEntryMonitor which implements QFileSystemWatcher
- Watches the desktop entry target directories
Connect monitor to DesktopEntryManager and add a new signal applicationsChanged
- On directory updated, it re-fetches the entries and emits the signal

outfoxxed · 2025-07-14T23:36:19Z

I'm generally conflicted on this one because I prefer state change notifications to manually triggered scanning, which often leads to polling.

As I'm aware, similar GTK based tools usually listen to a signal provided by glib/gio for this. I've been planning to check what that does and implement it here if feasible, as an alternative to re-scanning. If you're interested in figuring it out, https://github.com/GNOME/glib/blob/6e2a31f97a345e0a6b57a0c5c9f9b7514d61b755/gio/gappinfo.c#L2010 is probably a good place to start.

Looks like its just a simple directory watch, but it likely has to be recursive on every potential desktop entry dir, otherwise it's unlikely to handle nix generation switches and such.

This is the general direction I'd like to take it in. No pressure on you to implement it if you don't want to.

outfoxxed

I see you've marked it as WIP. Partial review

src/core/desktopentrymonitor.cpp

outfoxxed · 2025-07-15T03:13:23Z

src/core/desktopentrymonitor.cpp

+void DesktopEntryMonitor::addDirectoryHierarchy(const QString& dirPath) {
+	this->scanAndWatch(dirPath);
+}


outfoxxed · 2025-07-15T03:13:58Z

src/core/desktopentrymonitor.cpp

+	this->watcher = new QFileSystemWatcher(this);
+	this->debounceTimer = new QTimer(this);
+	this->debounceTimer->setSingleShot(true);
+	this->debounceTimer->setInterval(500); // 500ms debounce


500ms is unreasonably long for a debounce

outfoxxed · 2025-07-15T03:14:18Z

src/core/desktopentrymonitor.cpp

+	connect(
+	    this->watcher,
+	    &QFileSystemWatcher::directoryChanged,
+	    this,
+	    &DesktopEntryMonitor::onDirectoryChanged
+	);
+	connect(
+	    this->watcher,
+	    &QFileSystemWatcher::fileChanged,
+	    this,
+	    &DesktopEntryMonitor::onFileChanged
+	);
+	connect(this->debounceTimer, &QTimer::timeout, this, &DesktopEntryMonitor::processChanges);


QObject::connect

outfoxxed · 2025-07-15T03:14:39Z

src/core/desktopentrymonitor.cpp

+}
+
+void DesktopEntryMonitor::scanAndWatch(const QString& dirPath) {
+	QDir dir(dirPath);


disallowed style, use auto

outfoxxed · 2025-07-15T03:16:16Z

src/core/desktopentrymonitor.cpp

+	this->scanAndWatch(dirPath);
+}
+
+void DesktopEntryMonitor::scanAndWatch(const QString& dirPath) {


scanAndWatch + all the various change handlers share a lot of the code. consider initialization to be a diff from an empty set of entries and share the code.

outfoxxed · 2025-07-15T03:17:51Z

src/core/desktopentrymonitor.cpp

+			if (watchedFile.startsWith(path + "/") || watchedFile == path) {
+				this->watcher->removePath(watchedFile);
+				this->fileTimestamps.remove(watchedFile);
+				this->queueChange(ChangeEvent::Removed, watchedFile);


The debounce is not used in a logical way. If you are going to debounce, it should guard re-scanning directories, not model updates.

outfoxxed · 2025-07-15T03:18:39Z

src/core/desktopentrymonitor.cpp

+		for (auto it = this->watchedFiles.begin(); it != this->watchedFiles.end();) {
+			const QString& watchedFile = *it;


Why are we tracking watched files, the fs watcher already does that

outfoxxed · 2025-07-15T03:18:51Z

src/core/desktopentrymonitor.cpp

+		return;
+	}
+
+	QList<QString> currentFiles = dir.entryList({"*.desktop"}, QDir::Files);


bbedward · 2025-07-15T03:41:42Z

@outfoxxed I addressed the comments, I had it initially watching .desktop files and then decided against it, to just watch the directories and rescan when there's a change instead.

Sorry for the confusion, not wip anymore - ready for review

De-dupe code paths to scanAndWatch function, Optimize lookups by using a QSet, remove paths from watcher if deleted

- Create less fs watchers - Just re-scan when a directory containing .desktop files changes

Purian23 · 2025-07-19T04:30:55Z

Would there be anything holding this one up for primetime? It will be quite useful.

outfoxxed

Additional notes:

Please don't add useless comments
Please do scanning triggered by a change in another thread via QRunnable. The desktop entry scanner takes long enough to run that it may have a noticeable stutter on some systems without it.

outfoxxed · 2025-07-19T21:10:53Z

src/core/desktopentrymonitor.cpp

+void DesktopEntryMonitor::onDirectoryChanged(const QString& path) {
+	qCDebug(logDesktopMonitor) << "Directory changed:" << path;
+	auto dir = QDir(path);
+
+	// Check if directory still exists - handle removal/unmounting
+	if (!dir.exists()) {
+		qCDebug(logDesktopMonitor) << "Directory no longer exists, cleaning up:" << path;
+		this->watcher->removePath(path);
+		// Directory removal will be handled by full rescan
+		this->queueChange(ChangeEvent::Modified, path); // Trigger full rescan
+		return;
+	}
+
+	// Check for new subdirectories
+	auto subdirs = dir.entryList(QDir::Dirs | QDir::NoDotAndDotDot);
+	for (const QString& subdir: subdirs) {
+		auto subdirPath = dir.absoluteFilePath(subdir);
+		if (!this->watcher->directories().contains(subdirPath)) {
+			this->scanAndWatch(subdirPath);
+		}
+	}
+
+	// Queue a change to trigger full rescan of all desktop paths
+	this->queueChange(ChangeEvent::Modified, path);
+}
+
+void DesktopEntryMonitor::queueChange(ChangeEvent event, const QString& path) {
+	this->pendingChanges.insert(path, event);
+	this->debounceTimer->start();
+}


Instead of pending changes or tracking, if we're going to do a full rescan anyway then this should do nothing more than set a flag, and potentially bump the debounce timer for a rescan. The timer should be no more than 100ms

outfoxxed · 2025-07-19T21:21:01Z

src/core/desktopentry.cpp

+void DesktopEntryManager::handleFileChanges(
+    const QHash<QString, DesktopEntryMonitor::ChangeEvent>&
+) {
+	qCDebug(logDesktopEntry) << "Directory change detected, performing full rescan";
+
+	auto oldEntries = this->desktopEntries;
+
+	this->desktopEntries.clear();
+	this->lowercaseDesktopEntries.clear();
+
+	this->scanDesktopEntries();
+
+	QVector<DesktopEntry*> newApplications;
+	for (auto& entry: this->desktopEntries.values()) {
+		if (!entry->noDisplay()) {
+			newApplications.append(entry);
+		}
+	}
+
+	this->mApplications.diffUpdate(newApplications);
+
+	for (auto* e: oldEntries) {
+		if (!this->desktopEntries.contains(e->mId)) {
+			e->deleteLater();
+		}
+	}
+
+	emit applicationsChanged();
+}


Same comment as directory changed

outfoxxed · 2025-07-19T21:22:00Z

src/core/desktoputils.hpp

+#include <qstringlist.h>
+
+namespace DesktopUtils {
+QList<QString> getDesktopDirectories();


I am not sure why this was extracted into a new file

bbedward changed the title ~~core: add rescan method to DesktopEntryManager~~ core: add file system watcher for desktop entries Jul 15, 2025

bbedward changed the title ~~core: add file system watcher for desktop entries~~ (wip) core: add file system watcher for desktop entries Jul 15, 2025

bbedward changed the title ~~(wip) core: add file system watcher for desktop entries~~ (wip/donotmerge) core/desktopentry: add file system watcher for desktop entry directories Jul 15, 2025

bbedward changed the title ~~(wip/donotmerge) core/desktopentry: add file system watcher for desktop entry directories~~ core/desktopentry: add file system watcher for desktop entry directories Jul 15, 2025

outfoxxed requested changes Jul 15, 2025

View reviewed changes

bbedward requested a review from outfoxxed July 15, 2025 14:29

bbedward added 7 commits July 16, 2025 12:02

Add rescan option for DesktopEntryManager

e6ea6b6

More comprehensive DesktopEntry monitoring with QFileSystemWatcher

ab1e455

Cleanup and optimizations

537d415

De-dupe code paths to scanAndWatch function, Optimize lookups by using a QSet, remove paths from watcher if deleted

Use extractIdFromPath helper in scanPath

d6ab231

Only watch the desktop folders

0bbce67

- Create less fs watchers - Just re-scan when a directory containing .desktop files changes

consistency cleanups

daa7f93

use auto everywhere

b9cbcd2

bbedward force-pushed the master branch from dcffeec to b9cbcd2 Compare July 16, 2025 16:02

outfoxxed requested changes Jul 19, 2025

View reviewed changes

		for (auto it = this->watchedFiles.begin(); it != this->watchedFiles.end();) {
		const QString& watchedFile = *it;

core/desktopentry: add file system watcher for desktop entry directories #114

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core/desktopentry: add file system watcher for desktop entry directories #114

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bbedward commented Jul 15, 2025

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Purian23 commented Jul 19, 2025

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bbedward commented Jul 14, 2025 •

edited

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outfoxxed commented Jul 14, 2025 •

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