a

diff --git a/bin/image.sh b/bin/image.sh
index 7a8d7fb..40ee452 100755
--- a/bin/image.sh
+++ b/bin/image.sh
@@ -7,7 +7,7 @@ else
 fi
 
 DIR=$(dirname "$0")
-IMAGE=vitorenesduarte/vcd-java-client:${TAG}
+IMAGE=0track/vcd-java-client:${TAG}
 DOCKERFILE=${DIR}/../Dockerfiles/vcd-java-client
 
 # release vcd-java-client
diff --git a/src/main/java/org/imdea/vcd/DataRW.java b/src/main/java/org/imdea/vcd/DataRW.java
index 6b6eb55..ea9cf2a 100644
--- a/src/main/java/org/imdea/vcd/DataRW.java
+++ b/src/main/java/org/imdea/vcd/DataRW.java
@@ -6,12 +6,21 @@ import com.codahale.metrics.MetricAttribute;
 import com.codahale.metrics.MetricRegistry;
 import com.codahale.metrics.Timer;
 import com.google.protobuf.ByteString;
+import org.imdea.vcd.pb.Proto.Commit;
 import org.imdea.vcd.pb.Proto.Message;
 import org.imdea.vcd.pb.Proto.MessageSet;
 import org.imdea.vcd.pb.Proto.Reply;
-import org.imdea.vcd.queue.box.CommittedQueueBox;
+import org.imdea.vcd.queue.ConfQueue;
 import org.imdea.vcd.queue.DepQueue;
+import org.imdea.vcd.queue.Queue;
+import org.imdea.vcd.queue.QueueAddArgs;
+import org.imdea.vcd.queue.QueueType;
+import org.imdea.vcd.queue.RandomQueue;
+import org.imdea.vcd.queue.box.CommittedQueueBox;
 import org.imdea.vcd.queue.clock.Clock;
+import org.imdea.vcd.queue.clock.Dot;
+import org.imdea.vcd.queue.clock.ExceptionSet;
+import org.imdea.vcd.queue.clock.MaxInt;
 
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
@@ -22,19 +31,11 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
-import org.imdea.vcd.pb.Proto.Commit;
-import org.imdea.vcd.queue.ConfQueue;
-import org.imdea.vcd.queue.Queue;
-import org.imdea.vcd.queue.QueueAddArgs;
-import org.imdea.vcd.queue.QueueType;
-import org.imdea.vcd.queue.RandomQueue;
-import org.imdea.vcd.queue.clock.Dot;
-import org.imdea.vcd.queue.clock.ExceptionSet;
-import org.imdea.vcd.queue.clock.MaxInt;
 
 /**
  *
@@ -68,6 +69,7 @@ public class DataRW {
 
     private final LinkedBlockingQueue<MessageSet> toWriter;
     private final LinkedBlockingQueue<Optional<MessageSet>> toClient;
+    private final Set<ByteString> chains;
     private final Writer writer;
     private final SocketReader socketReader;
 
@@ -77,8 +79,9 @@ public class DataRW {
         this.batchWait = config.getBatchWait();
         this.toWriter = new LinkedBlockingQueue<>();
         this.toClient = new LinkedBlockingQueue<>();
+        this.chains =  ConcurrentHashMap.newKeySet();
         this.writer = new Writer(this.out, this.toWriter, this.batchWait);
-        this.socketReader = new SocketReader(this.in, this.toClient, config);
+        this.socketReader = new SocketReader(this.in, this.toClient, this.chains, config);
     }
 
     public void start() {
@@ -111,6 +114,20 @@ public class DataRW {
         if (this.batchWait > 0) {
             toWriter.put(messageSet);
         } else {
+            boolean canWrite;
+            do {
+                canWrite = true;
+                mainLoop:
+                for (Message message : messageSet.getMessagesList()) {
+                    for (ByteString hash : message.getHashesList()) {
+                        if (chains.contains(hash)){
+                            canWrite = false;
+                            break mainLoop;
+                        }
+                    }
+                }
+                if (!canWrite) Thread.sleep(1);
+            } while (!canWrite);
             doWrite(messageSet, this.out);
         }
     }
@@ -208,12 +225,12 @@ public class DataRW {
         private final LinkedBlockingQueue<Reply> toDeliverer;
         private final Deliverer deliverer;
 
-        public SocketReader(DataInputStream in, LinkedBlockingQueue<Optional<MessageSet>> toClient, Config config) {
+        public SocketReader(DataInputStream in, LinkedBlockingQueue<Optional<MessageSet>> toClient, Set<ByteString> chains, Config config) {
             this.in = in;
             this.toClient = toClient;
             this.batchWait = config.getBatchWait();
             this.toDeliverer = new LinkedBlockingQueue<>();
-            this.deliverer = new Deliverer(this.toClient, this.toDeliverer, config);
+            this.deliverer = new Deliverer(this.toClient, chains, this.toDeliverer, config);
         }
 
         public void close() {
@@ -281,6 +298,7 @@ public class DataRW {
         private final Sorter sorter;
         private final QueueType queueType;
         private Queue<CommittedQueueBox> queue;
+        private final Set<ByteString> chains;
 
         // metrics
         private final Timer toAdd;
@@ -289,7 +307,7 @@ public class DataRW {
         private final Histogram queueSize;
         private final Histogram queueElements;
 
-        public Deliverer(LinkedBlockingQueue<Optional<MessageSet>> toClient, LinkedBlockingQueue<Reply> toDeliverer, Config config) {
+        public Deliverer(LinkedBlockingQueue<Optional<MessageSet>> toClient, Set<ByteString> chains,LinkedBlockingQueue<Reply> toDeliverer, Config config) {
 
             createBox = METRICS.timer(MetricRegistry.name(DataRW.class, "createBox"));
             toAdd = METRICS.timer(MetricRegistry.name(DataRW.class, "toAdd"));
@@ -302,6 +320,7 @@ public class DataRW {
             this.toSorter = new LinkedBlockingQueue<>();
             this.sorter = new Sorter(toClient, this.toSorter, config);
             this.queueType = config.getQueueType();
+            this.chains = chains;
         }
 
         public void close() {
@@ -354,7 +373,14 @@ public class DataRW {
                             queueElements.update(queue.elements());
 
                             if (!toDeliver.isEmpty()) {
+                                for (Message message : queue.first().getMessages()) {
+                                    chains.removeAll(message.getHashesList());
+                                }
                                 toSorter.put(toDeliver);
+                            }else if (queue.size() > 0) {
+                                for (Message message : queue.first().getMessages()) {
+                                    chains.addAll(message.getHashesList());
+                                }
                             }
                             break;
                         default:
diff --git a/src/main/java/org/imdea/vcd/queue/ConfQueue.java b/src/main/java/org/imdea/vcd/queue/ConfQueue.java
index 8a0d880..3f907fa 100644
--- a/src/main/java/org/imdea/vcd/queue/ConfQueue.java
+++ b/src/main/java/org/imdea/vcd/queue/ConfQueue.java
@@ -1,19 +1,19 @@
 package org.imdea.vcd.queue;
 
+import org.imdea.vcd.queue.box.QueueBox;
+import org.imdea.vcd.queue.clock.Clock;
+import org.imdea.vcd.queue.clock.Dot;
+import org.imdea.vcd.queue.clock.Dots;
+import org.imdea.vcd.queue.clock.ExceptionSet;
+
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Deque;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import org.imdea.vcd.queue.box.QueueBox;
-import org.imdea.vcd.queue.clock.Clock;
-import org.imdea.vcd.queue.clock.Dot;
-import org.imdea.vcd.queue.clock.Dots;
-import org.imdea.vcd.queue.clock.ExceptionSet;
 
 /**
  *
@@ -26,6 +26,7 @@ public class ConfQueue<E extends QueueBox> implements Queue<E> {
     private final HashMap<Dot, E> dotToBox = new HashMap<>();
     private final HashMap<Dot, Clock<ExceptionSet>> dotToConf = new HashMap<>();
     private List<E> toDeliver = new ArrayList<>();
+    E first;
 
     private final Clock<ExceptionSet> committed;
     private final Clock<ExceptionSet> delivered;
@@ -139,6 +140,11 @@ public class ConfQueue<E extends QueueBox> implements Queue<E> {
         throw new UnsupportedOperationException("Method not supported.");
     }
 
+    @Override
+    public E first() {
+        return first;
+    }
+
     @Override
     public int size() {
         return this.dotToConf.size();
@@ -183,6 +189,8 @@ public class ConfQueue<E extends QueueBox> implements Queue<E> {
             // get conf
             Clock<ExceptionSet> conf = dotToConf.get(at);
 
+            first = dotToBox.get(at);
+
             // if not all deps are committed, give up
             boolean allDepsCommitted = conf.subtractIsBottom(committed);
             if (!allDepsCommitted) {
diff --git a/src/main/java/org/imdea/vcd/queue/DepQueue.java b/src/main/java/org/imdea/vcd/queue/DepQueue.java
index b9c34aa..f2d308b 100644
--- a/src/main/java/org/imdea/vcd/queue/DepQueue.java
+++ b/src/main/java/org/imdea/vcd/queue/DepQueue.java
@@ -133,6 +133,11 @@ public class DepQueue<E extends QueueBox> implements Queue<E> {
         return result;
     }
 
+    @Override
+    public E first() {
+        return first.item;
+    }
+
     /**
      * Find element that depends on e.
      */
diff --git a/src/main/java/org/imdea/vcd/queue/Queue.java b/src/main/java/org/imdea/vcd/queue/Queue.java
index 0eba674..8f17b9c 100644
--- a/src/main/java/org/imdea/vcd/queue/Queue.java
+++ b/src/main/java/org/imdea/vcd/queue/Queue.java
@@ -18,6 +18,8 @@ public interface Queue<E extends QueueBox> {
 
     List<E> toList();
 
+    E first();
+
     int size();
 
     int elements();
diff --git a/src/main/java/org/imdea/vcd/queue/RandomQueue.java b/src/main/java/org/imdea/vcd/queue/RandomQueue.java
index 4a1499f..cf108c7 100644
--- a/src/main/java/org/imdea/vcd/queue/RandomQueue.java
+++ b/src/main/java/org/imdea/vcd/queue/RandomQueue.java
@@ -1,11 +1,12 @@
 package org.imdea.vcd.queue;
 
+import org.imdea.vcd.queue.box.QueueBox;
+
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ThreadLocalRandom;
-import org.imdea.vcd.queue.box.QueueBox;
 
 /**
  *
@@ -68,6 +69,11 @@ public class RandomQueue<E extends QueueBox> implements Queue<E> {
         throw new UnsupportedOperationException("Method not supported.");
     }
 
+    @Override
+    public E first() {
+        return this.toList().get(0);
+    }
+
     @Override
     public int size() {
         return size;