1 files changed, 18 insertions, 3 deletions

diff --git a/src/org/traccar/database/DataCache.java b/src/org/traccar/database/DataCache.java
index f5aa3b1e9..f28f1b838 100644
--- a/src/org/traccar/database/DataCache.java
+++ b/src/org/traccar/database/DataCache.java
@@ -18,6 +18,8 @@ package org.traccar.database;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import org.traccar.model.Position;
@@ -31,7 +33,7 @@ public class DataCache {
         // TODO: load latest data from datavase
     }
     
-    public void update(Position position) {
+    public synchronized void update(Position position) {
         long device = position.getDeviceId();
         positions.put(device, position);
         if (listeners.containsKey(device)) {
@@ -41,6 +43,19 @@ public class DataCache {
         }
     }
     
+    public synchronized Collection<Position> getInitialState(Collection<Long> devices) {
+        
+        List<Position> result = new LinkedList<Position>();
+        
+        for (long device : devices) {
+            if (positions.containsKey(device)) {
+                result.add(positions.get(device));
+            }
+        }
+        
+        return result;
+    }
+    
     public static interface DataCacheListener {
         public void onUpdate(Position position);
     }
@@ -51,7 +66,7 @@ public class DataCache {
         }
     }
     
-    public void addListener(long device, DataCacheListener listener) {
+    public synchronized void addListener(long device, DataCacheListener listener) {
         if (!listeners.containsKey(device)) {
             listeners.put(device, new HashSet<DataCacheListener>());
         }
@@ -64,7 +79,7 @@ public class DataCache {
         }
     }
     
-    public void removeListener(long device, DataCacheListener listener) {
+    public synchronized void removeListener(long device, DataCacheListener listener) {
         if (!listeners.containsKey(device)) {
             listeners.put(device, new HashSet<DataCacheListener>());
         }