Reload TrackerList when hosts are automatically updated (#502)

* Initial plan

* Add TrackerList reload when hosts are updated

- Add reloadTrackerData() method to TrackerList to clear and reload tracker data
- Change trackingIps from HashSet to ConcurrentHashMap.newKeySet() for thread safety
- Call reloadTrackerData() from prepareHostsBlocked() after hosts are reloaded
- Invalidate tracker count cache when tracker data is reloaded
- Ensures TrackerList stays in sync with updated hosts from automatic downloads

Co-authored-by: kasnder <5175206+kasnder@users.noreply.github.com>

* Address code review feedback

- Use getInstance(c) in reloadTrackerData() to ensure instance is created
- Fix ActivitySettings to use reloadTrackerData() instead of loadTrackers()
  to properly clear old data when domain_based_blocked setting changes

Co-authored-by: kasnder <5175206+kasnder@users.noreply.github.com>

* Add synchronization to reloadTrackerData()

- Add reloadLock to synchronize tracker data reload operations
- Wrap entire reload operation in synchronized block to prevent race conditions
- Ensures atomic clear and reload of tracker data

Co-authored-by: kasnder <5175206+kasnder@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: kasnder <5175206+kasnder@users.noreply.github.com>

Author: Copilot

app/src/main/java/eu/faircode/netguard/ActivitySettings.java

@@ -715,8 +715,7 @@ else if ("loglevel".equals(name))
             ServiceSinkhole.reload("changed " + name, this, false);
 
         else if ("domain_based_blocked".equals(name)) {
-            TrackerList ts = TrackerList.getInstance(this);
-            ts.loadTrackers(this);
+            TrackerList.reloadTrackerData(this);
         }
 
     }

app/src/main/java/eu/faircode/netguard/ServiceSinkhole.java

@@ -1799,6 +1799,9 @@ public static void prepareHostsBlocked(Context c) {
         }
 
         lock.writeLock().unlock();
+        
+        // Reload TrackerList to ensure it stays in sync with updated hosts
+        TrackerList.reloadTrackerData(c);
     }
 
     private void prepareUidIPFilters(String dname) {

app/src/main/java/net/kollnig/missioncontrol/data/TrackerList.java

@@ -58,12 +58,15 @@ public class TrackerList {
     private static final String TAG = TrackerList.class.getSimpleName();
     private static final List<String> ignoreDomains = Collections.singletonList("cloudfront.net, fastly.net");
     private static final Map<String, Tracker> hostnameToTracker = new ConcurrentHashMap<>();
-    public static Set<String> trackingIps = new HashSet<>();
+    public static Set<String> trackingIps = ConcurrentHashMap.newKeySet();
     public static String TRACKER_HOSTLIST = "TRACKER_HOSTLIST";
     private static final Tracker hostlistTracker = new Tracker(TRACKER_HOSTLIST, UNCATEGORISED);
     private static TrackerList instance;
     private static boolean domainBasedBlocking;
     private final DatabaseHelper databaseHelper;
+    
+    // Lock for synchronizing tracker data reload operations
+    private static final Object reloadLock = new Object();
 
     // Performance: Cache tracker counts to avoid full DB scans on every refresh
     private Pair<Pair<Map<Integer, Integer>, Integer>, Pair<Map<Integer, Integer>, Integer>> cachedTrackerCounts;
@@ -130,6 +133,30 @@ public static Tracker findTracker(@NonNull String hostname) {
         return t;
     }
 
+    /**
+     * Reload tracker data by clearing all existing data and reloading from assets.
+     * This should be called when the hosts blocklist is updated to ensure TrackerList
+     * stays in sync with the updated hosts.
+     *
+     * @param c Context
+     */
+    public static void reloadTrackerData(Context c) {
+        Log.i(TAG, "Reloading tracker data");
+        
+        // Synchronize the entire reload operation to prevent race conditions
+        synchronized (reloadLock) {
+            // Clear existing data (both are thread-safe collections)
+            hostnameToTracker.clear();
+            trackingIps.clear();
+            
+            // Ensure instance exists and reload trackers from assets
+            TrackerList trackerList = getInstance(c);
+            trackerList.loadTrackers(c);
+            // Invalidate cached tracker counts since tracker data has changed
+            trackerList.invalidateTrackerCountCache();
+        }
+    }
+
     /**
      * Load tracker domain database
      *