♻️ Rework FSNotifier and test it

PHP Monitor.xcodeproj/project.pbxproj

@@ -74,6 +74,7 @@
 		0379C4A52ED720220035D7EA /* App+DetectApps.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0379C4A32ED7201D0035D7EA /* App+DetectApps.swift */; };
 		0379C4A62ED720220035D7EA /* App+DetectApps.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0379C4A32ED7201D0035D7EA /* App+DetectApps.swift */; };
 		0379C4A72ED720220035D7EA /* App+DetectApps.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0379C4A32ED7201D0035D7EA /* App+DetectApps.swift */; };
+		037F44162EDB0AAA002EBF75 /* FSNotifierTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 037F44152EDB0AA8002EBF75 /* FSNotifierTest.swift */; };
 		0386B0B42ED36C3D00CA6795 /* Locked.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0386B0B32ED36C3D00CA6795 /* Locked.swift */; };
 		0386B0B52ED36C3D00CA6795 /* Locked.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0386B0B32ED36C3D00CA6795 /* Locked.swift */; };
 		0386B0B62ED36C3D00CA6795 /* Locked.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0386B0B32ED36C3D00CA6795 /* Locked.swift */; };
@@ -1050,6 +1051,7 @@
 		036C39132E5CB820008DAEDF /* TestBundle.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TestBundle.swift; sourceTree = "<group>"; };
 		0379C49E2ED71CFC0035D7EA /* Startup+Launch.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Startup+Launch.swift"; sourceTree = "<group>"; };
 		0379C4A32ED7201D0035D7EA /* App+DetectApps.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "App+DetectApps.swift"; sourceTree = "<group>"; };
+		037F44152EDB0AA8002EBF75 /* FSNotifierTest.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FSNotifierTest.swift; sourceTree = "<group>"; };
 		0386B0B32ED36C3D00CA6795 /* Locked.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Locked.swift; sourceTree = "<group>"; };
 		0386B0B82ED36DF800CA6795 /* LockedTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LockedTests.swift; sourceTree = "<group>"; };
 		0392CDE52EB23B8F009176DA /* CertificateValidator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CertificateValidator.swift; sourceTree = "<group>"; };
@@ -1457,6 +1459,14 @@
 			path = Parsers;
 			sourceTree = "<group>";
 		};
+		037F44142EDB0A9F002EBF75 /* Watchers */ = {
+			isa = PBXGroup;
+			children = (
+				037F44152EDB0AA8002EBF75 /* FSNotifierTest.swift */,
+			);
+			path = Watchers;
+			sourceTree = "<group>";
+		};
 		0386B0BD2ED36E2500CA6795 /* Helpers */ = {
 			isa = PBXGroup;
 			children = (
@@ -2435,6 +2445,7 @@
 				03D53E902E8AE089001B1671 /* Testables */,
 				036575C62EA12E2200BA41BF /* Versions */,
 				0386B0BD2ED36E2500CA6795 /* Helpers */,
+				037F44142EDB0A9F002EBF75 /* Watchers */,
 			);
 			path = unit;
 			sourceTree = "<group>";
@@ -3523,6 +3534,7 @@
 				C485707A28BF457800539B36 /* PhpDoctorView.swift in Sources */,
 				C4C0E8E827F88B41002D32A9 /* DomainScanner.swift in Sources */,
 				C449B4F027EE7FB800C47E8A /* DomainListTLSCell.swift in Sources */,
+				037F44162EDB0AAA002EBF75 /* FSNotifierTest.swift in Sources */,
 				C4FBFC532616485F00CDB8E1 /* PhpVersionDetectionTest.swift in Sources */,
 				C43A8A2425D9D20D00591B77 /* HomebrewPackageTest.swift in Sources */,
 				C485707928BF456C00539B36 /* ArrayExtension.swift in Sources */,

phpmon/Common/Helpers/Locked.swift

@@ -34,7 +34,7 @@ import Foundation
  situations where adopting structured concurrency would otherwise be
  too challenging or a huge refactor.
  */
-final class Locked<T> {
+final class Locked<T>: @unchecked Sendable {
     private var _value: T
     private let lock = NSLock()
 

phpmon/Domain/Watcher/FSNotifier.swift

@@ -42,18 +42,27 @@ class FSNotifier {
         )
 
         dispatchSource?.setEventHandler(handler: {
-            let distance = self.lastUpdate?.distance(to: Date().timeIntervalSince1970)
+            self.queue.async {
+                // See how long ago our last handled event was
+                let distance = self.lastUpdate?
+                    .distance(to: Date().timeIntervalSince1970)
 
-            if distance == nil || distance != nil && distance! > 1.00 {
-                // FS event fired, checking in 1s, no duplicate FS events will be acted upon
+                // Add a debounce of 1 second
+                if let distance, distance <= 1.00 {
+                    Log.perf("FSNotifier debounce active for \(url.path).")
+                    return
+                }
+
+                // Synchronize the last update property
                 self.lastUpdate = Date().timeIntervalSince1970
 
+                // Dispatch the async task we set for when the filesystem event occurs
                 Task {
-                    await delay(seconds: 1)
                     onChange()
                 }
             }
         })
+
         dispatchSource?.setCancelHandler(handler: { [weak self] in
             guard let self = self else { return }
 
@@ -61,6 +70,7 @@ class FSNotifier {
             self.fileDescriptor = -1
             self.dispatchSource = nil
         })
+
         dispatchSource?.resume()
     }
 

tests/unit/Watchers/FSNotifierTest.swift

@@ -0,0 +1,58 @@
+//
+//  FSNotifierTest.swift
+//  PHP Monitor
+//
+//  Created by Nico Verbruggen on 29/11/2025.
+//  Copyright © 2025 Nico Verbruggen. All rights reserved.
+//
+
+import Testing
+import Foundation
+
+@Suite(.serialized)
+struct FSNotifierTest {
+    /**
+     This test verifies that FSNotifier fires the onChange callback when a file is modified.
+     */
+    @Test func notifier_fires_when_file_is_modified_and_debounces_correctly() async throws {
+        // Create a temporary file to monitor
+        let tempDir = FileManager.default.temporaryDirectory
+        let testFile = tempDir.appendingPathComponent("fs_notifier_test_\(UUID().uuidString).txt")
+        FileManager.default.createFile(atPath: testFile.path, contents: nil)
+
+        defer {
+            try? FileManager.default.removeItem(at: testFile)
+        }
+
+        let eventFired = Locked<Int>(0)
+
+        // Create notifier
+        let notifier = FSNotifier(
+            for: testFile,
+            eventMask: .write,
+            onChange: {
+                eventFired.value += 1
+            }
+        )
+
+        defer {
+            notifier.terminate()
+        }
+
+        // Modify the file, twice
+        try "hello".write(to: testFile, atomically: false, encoding: .utf8)
+        try "hello".write(to: testFile, atomically: false, encoding: .utf8)
+
+        // Wait for the event to fire, verify it fired ONCE (not TWICE)
+        try await Task.sleep(nanoseconds: 200_000_000) // 0.2 seconds
+        #expect(eventFired.value == 1)
+
+        // Try to write again (after debounce timing)
+        try await Task.sleep(nanoseconds: 2_000_000_000)
+        try "hello".write(to: testFile, atomically: false, encoding: .utf8)
+
+        // Verify our event fired AGAIN after 0.2 seconds
+        try await Task.sleep(nanoseconds: 200_000_000) // 0.2 seconds
+        #expect(eventFired.value == 2)
+    }
+}