[Java] fix concurrent modification exception for EQ cache

sdk-java/src/main/java/ly/count/sdk/java/internal/EventQueue.java

@@ -1,30 +1,39 @@
 package ly.count.sdk.java.internal;
 
-import ly.count.sdk.java.Countly;
-import javax.annotation.Nonnull;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import javax.annotation.Nonnull;
 
 public class EventQueue {
 
     static final String DELIMITER = ":::";
     Log L;
     List<EventImpl> eventQueueMemoryCache;
 
+    protected final Object lockEQ = new Object();
+
     protected EventQueue() {
     }
 
-    protected EventQueue(@Nonnull Log logger, int eventThreshold) {
+    protected EventQueue(@Nonnull Log logger) {
         L = logger;
-        eventQueueMemoryCache = new ArrayList<>(eventThreshold);
+        eventQueueMemoryCache = new ArrayList<>();
     }
 
     /**
      * Returns the number of events currently stored in the queue.
      */
     protected int eqSize() {
-        return eventQueueMemoryCache.size();
+        synchronized (lockEQ) {
+            return eventQueueMemoryCache.size();
+        }
+    }
+
+    protected List<EventImpl> getEQ() {
+        synchronized (lockEQ) {
+            return new ArrayList<>(eventQueueMemoryCache);
+        }
     }
 
     void addEvent(@Nonnull final EventImpl event) {
@@ -33,8 +42,10 @@ void addEvent(@Nonnull final EventImpl event) {
             return;
         }
         L.d("[EventQueue] Adding event: " + event.key);
-        eventQueueMemoryCache.add(event);
-        writeEventQueueToStorage();
+        synchronized (lockEQ) {
+            eventQueueMemoryCache.add(event);
+            writeEventQueueToStorage();
+        }
     }
 
     /**
@@ -56,20 +67,22 @@ void writeEventQueueToStorage() {
      * Restores events from disk
      */
     void restoreFromDisk() {
-        L.d("[EventQueue] Restoring events from disk");
-        eventQueueMemoryCache.clear();
-
-        final String[] array = getEvents();
-        for (String s : array) {
-
-            final EventImpl event = EventImpl.fromJSON(s, (ev) -> {
-            }, L);
-            if (event != null) {
-                eventQueueMemoryCache.add(event);
+        synchronized (lockEQ) {
+            L.d("[EventQueue] Restoring events from disk");
+            eventQueueMemoryCache.clear();
+
+            final String[] array = getEvents();
+            for (String s : array) {
+
+                final EventImpl event = EventImpl.fromJSON(s, (ev) -> {
+                }, L);
+                if (event != null) {
+                    eventQueueMemoryCache.add(event);
+                }
             }
+            // order the events from least to most recent
+            eventQueueMemoryCache.sort((e1, e2) -> (int) (e1.timestamp - e2.timestamp));
         }
-        // order the events from least to most recent
-        eventQueueMemoryCache.sort((e1, e2) -> (int) (e1.timestamp - e2.timestamp));
     }
 
     @Nonnull String joinEvents(@Nonnull final Collection<EventImpl> collection) {
@@ -91,6 +104,8 @@ void restoreFromDisk() {
 
     public void clear() {
         SDKCore.instance.sdkStorage.storeEventQueue("");
-        eventQueueMemoryCache.clear();
+        synchronized (lockEQ) {
+            eventQueueMemoryCache.clear();
+        }
     }
 }

sdk-java/src/main/java/ly/count/sdk/java/internal/ModuleEvents.java

@@ -17,7 +17,7 @@ public class ModuleEvents extends ModuleBase {
     public void init(InternalConfig config) {
         super.init(config);
         L.d("[ModuleEvents] init: config = " + config);
-        eventQueue = new EventQueue(L, config.getEventsBufferSize());
+        eventQueue = new EventQueue(L);
         eventQueue.restoreFromDisk();
         eventsInterface = new Events();
     }
@@ -69,7 +69,7 @@ public void stop(InternalConfig config, final boolean clear) {
     private synchronized void addEventsToRequestQ(String deviceId) {
         L.d("[ModuleEvents] addEventsToRequestQ");
 
-        if (eventQueue.eventQueueMemoryCache.isEmpty()) {
+        if (eventQueue.getEQ().isEmpty()) {
             L.d("[ModuleEvents] addEventsToRequestQ, eventQueueMemoryCache is empty, skipping");
             return;
         }
@@ -78,7 +78,7 @@ private synchronized void addEventsToRequestQ(String deviceId) {
         if (deviceId != null) {
             request.params.add("device_id", deviceId);
         }
-        request.params.arr("events").put(eventQueue.eventQueueMemoryCache).add();
+        request.params.arr("events").put(eventQueue.getEQ()).add();
         request.own(ModuleEvents.class);
 
         eventQueue.clear();

sdk-java/src/test/java/ly/count/sdk/java/internal/EventQueueTests.java

@@ -34,7 +34,7 @@ public class EventQueueTests {
 
     private void init(Config cc) {
         Countly.instance().init(cc);
-        eventQueue = new EventQueue(L, cc.getEventsBufferSize());
+        eventQueue = new EventQueue(L);
     }
 
     @After