diff --git a/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractActor.java b/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractActor.java
index 2f9062ca7..b698d042a 100644
--- a/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractActor.java
+++ b/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractActor.java
@@ -36,7 +36,7 @@ public String getAddress() {
     }
 
     @Override
-    public boolean send(T message) {
+    public boolean offer(T message) {
         if (mailbox.offerUserMessage(message)) {
             dispatch();
             return true;
@@ -73,14 +73,15 @@ public ActorState getActorState() {
     @Override
     public void run() {
         while (true) {
-            handleSystemMessages();
+            boolean systemMailboxEmpty = handleSystemMessages();
 
             if (actorState == ActorState.PAUSE) {
                 break;
             }
 
-            boolean empty = handleUserMessages();
-            if (empty) {
+            boolean userMailboxEmpty = handleUserMessages();
+
+            if (systemMailboxEmpty && userMailboxEmpty) {
                 break;
             }
         }
@@ -124,7 +125,14 @@ private boolean handleUserMessages() {
         return empty;
     }
 
-    private void handleSystemMessages() {
+    protected void pauseInMessageProcessThread() {
+        if (actorState == ActorState.RUNNING) {
+            actorState = ActorState.PAUSE;
+        }
+    }
+
+    private boolean handleSystemMessages() {
+        boolean empty;
         SystemMessage systemMessage = mailbox.pollSystemMessage();
         if (systemMessage != null) {
             switch (systemMessage) {
@@ -147,7 +155,11 @@ private void handleSystemMessages() {
                     }
                     break;
             }
+            empty = false;
+        } else {
+            empty = true;
         }
+        return empty;
     }
 
     private void sendSystemMessage(SystemMessage message) {
@@ -221,8 +233,6 @@ public void dispatch(Runnable runnable) {
     public static class MailboxImpl<T> implements Mailbox<T, AbstractActor.SystemMessage> {
         private final Queue<T> userMessageQueue;
         private final Queue<AbstractActor.SystemMessage> systemMessageQueue;
-        private final AtomicInteger unhandledUserMessageCount = new AtomicInteger(0);
-        private final AtomicInteger unhandledSystemMessageCount = new AtomicInteger(0);
 
         public MailboxImpl(Queue<T> userMessageQueue, Queue<SystemMessage> systemMessageQueue) {
             this.userMessageQueue = userMessageQueue;
@@ -231,48 +241,32 @@ public MailboxImpl(Queue<T> userMessageQueue, Queue<SystemMessage> systemMessage
 
         @Override
         public AbstractActor.SystemMessage pollSystemMessage() {
-            AbstractActor.SystemMessage systemMessage = systemMessageQueue.poll();
-            if (systemMessage != null) {
-                unhandledSystemMessageCount.decrementAndGet();
-            }
-            return systemMessage;
+            return systemMessageQueue.poll();
         }
 
         @Override
         public boolean offerSystemMessage(AbstractActor.SystemMessage systemMessage) {
-            boolean success = systemMessageQueue.offer(systemMessage);
-            if (success) {
-                unhandledSystemMessageCount.incrementAndGet();
-            }
-            return success;
+            return systemMessageQueue.offer(systemMessage);
         }
 
         @Override
         public boolean hasSystemMessage() {
-            return unhandledSystemMessageCount.get() > 0;
+            return systemMessageQueue.peek() != null;
         }
 
         @Override
         public T pollUserMessage() {
-            T message = userMessageQueue.poll();
-            if (message != null) {
-                unhandledUserMessageCount.decrementAndGet();
-            }
-            return message;
+            return userMessageQueue.poll();
         }
 
         @Override
         public boolean offerUserMessage(T userMessage) {
-            boolean success = userMessageQueue.offer(userMessage);
-            if (success) {
-                unhandledUserMessageCount.incrementAndGet();
-            }
-            return success;
+            return userMessageQueue.offer(userMessage);
         }
 
         @Override
         public boolean hasUserMessage() {
-            return unhandledUserMessageCount.get() > 0;
+            return userMessageQueue.peek() != null;
         }
     }
 }
diff --git a/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractAsyncActor.java b/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractAsyncActor.java
index ffafaa672..cd170c17b 100644
--- a/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractAsyncActor.java
+++ b/firefly-common/src/main/java/com/fireflysource/common/actor/AbstractAsyncActor.java
@@ -16,7 +16,7 @@ public AbstractAsyncActor(String address, Dispatcher dispatcher, Mailbox<T, Syst
 
     @Override
     public void onReceive(T message) {
-        pause();
+        pauseInMessageProcessThread();
         onReceiveAsync(message).handle((result, throwable) -> {
             resume();
             return Result.DONE;
diff --git a/firefly-common/src/main/java/com/fireflysource/common/actor/Actor.java b/firefly-common/src/main/java/com/fireflysource/common/actor/Actor.java
index 8ad049c91..131fb9613 100644
--- a/firefly-common/src/main/java/com/fireflysource/common/actor/Actor.java
+++ b/firefly-common/src/main/java/com/fireflysource/common/actor/Actor.java
@@ -15,11 +15,11 @@ public interface Actor<T> {
     String getAddress();
 
     /**
-     * Send message to this actor.
+     * Offer message to this actor's mailbox.
      *
      * @param message The message.
-     * @return If true, send message success.
+     * @return If true, offer message success.
      */
-    boolean send(T message);
+    boolean offer(T message);
 
 }
diff --git a/firefly-common/src/test/java/com/fireflysource/common/actor/TestActor.java b/firefly-common/src/test/java/com/fireflysource/common/actor/TestActor.java
index 5b48c6750..ede25fdac 100644
--- a/firefly-common/src/test/java/com/fireflysource/common/actor/TestActor.java
+++ b/firefly-common/src/test/java/com/fireflysource/common/actor/TestActor.java
@@ -30,7 +30,7 @@ void test() throws Exception {
             log("Today sales amount: " + amount);
             return null;
         }));
-        store.send(closeMessage);
+        store.offer(closeMessage);
 
         CompletableFuture.allOf(results.stream().map(r -> r.handle((ignore, throwable) -> {
             Optional.ofNullable(throwable).map(Throwable::getMessage).ifPresent(System.out::println);
@@ -41,13 +41,13 @@ void test() throws Exception {
 
     private void stock(StoreActor store, String name, long price, int count) {
         IntStream.range(0, count).parallel()
-                 .forEach(i -> store.send(new StoreActor.StockMessage(new StoreActor.Product(name, price))));
+                 .forEach(i -> store.offer(new StoreActor.StockMessage(new StoreActor.Product(name, price))));
     }
 
     private List<CompletableFuture<Void>> purchase(StoreActor store, String name, long price, int count) {
         return IntStream.range(0, count).parallel().boxed().map(i -> {
             StoreActor.PurchaseMessage purchaseMessage = new StoreActor.PurchaseMessage(new StoreActor.Product(name, price));
-            store.send(purchaseMessage);
+            store.offer(purchaseMessage);
             return purchaseMessage.result.thenAccept(ignore -> log("purchase " + name + " success."));
         }).collect(Collectors.toList());
     }
diff --git a/pom.xml b/pom.xml
index 98bc7642f..cfeddfeb3 100644
--- a/pom.xml
+++ b/pom.xml
@@ -69,7 +69,7 @@
         <kotlin.code.style>official</kotlin.code.style>
 
         <!-- Kotlin doc configuration -->
-        <dokka.version>1.9.10</dokka.version>
+        <dokka.version>1.9.20</dokka.version>
         <dokka.config.noStdlibLink>true</dokka.config.noStdlibLink>
         <dokka.config.jdkVersion>8</dokka.config.jdkVersion>
 
@@ -324,7 +324,7 @@
                 <plugin>
                     <groupId>org.jacoco</groupId>
                     <artifactId>jacoco-maven-plugin</artifactId>
-                    <version>0.8.11</version>
+                    <version>0.8.12</version>
                     <dependencies>
                         <dependency>
                             <groupId>org.apache.maven.reporting</groupId>