Fix thread-safety bug in the writable sessions list

Author: pimterry

app/src/main/java/com/lipisoft/toyshark/SessionHandler.java

@@ -20,6 +20,7 @@
 import java.nio.ByteBuffer;
 import java.util.LinkedList;
 import java.util.Queue;
+import java.util.concurrent.ConcurrentLinkedQueue;
 
 import com.lipisoft.toyshark.network.ip.IPPacketFactory;
 import com.lipisoft.toyshark.network.ip.IPv4Header;
@@ -45,7 +46,7 @@ public class SessionHandler {
 
 	private static final SessionHandler handler = new SessionHandler();
 
-	private Queue<Session> writableSessionsQueue = new LinkedList<>();
+	private Queue<Session> writableSessionsQueue = new ConcurrentLinkedQueue<>();
 	private IClientPacketWriter writer;
 	private SocketData packetData;
 

app/src/main/java/com/lipisoft/toyshark/socket/SocketNIODataService.java

@@ -20,6 +20,7 @@
 import java.nio.channels.UnresolvedAddressException;
 import java.nio.channels.UnsupportedAddressTypeException;
 import java.util.Iterator;
+import java.util.Queue;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ThreadPoolExecutor;
@@ -112,16 +113,16 @@ private void runTask(){
 					}
 				}
 
-				while (SessionHandler.getInstance().getWritableSessions().size() != 0) {
-					Session session = SessionHandler.getInstance().getWritableSessions().remove();
+				Queue<Session> sessions = SessionHandler.getInstance().getWritableSessions();
 
+				Session session = sessions.poll();
+				while (session != null) {
 					if (session.isConnected()) {
 						processPendingWrite(session);
 					}
 
-					if (shutdown) {
-						break;
-					}
+					if (shutdown) break;
+					session = sessions.poll();
 				}
 			}
 		}