use ReadWriteLock instead of synchronized on class level

this will avoid a dead-lock when trying to close the session from session state listener.
See opentelecoms-org#193

Signed-off-by: Christian Ambach <ambi@samba.org>

jsmpp/src/main/java/org/jsmpp/session/SMPPSessionContext.java

@@ -17,31 +17,43 @@
 import org.jsmpp.extra.SessionState;
 import org.jsmpp.session.state.SMPPSessionState;
 
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
 /**
  * @author uudashr
  *
  */
 public class SMPPSessionContext extends AbstractSessionContext {
     private final SMPPSession smppSession;
     private SMPPSessionState stateProcessor = SMPPSessionState.CLOSED;
+
+    private ReadWriteLock stateProcessorLock = new ReentrantReadWriteLock();
 
     public SMPPSessionContext(SMPPSession smppSession,
             SessionStateListener sessionStateListener) {
         super(sessionStateListener);
         this.smppSession = smppSession;
     }
 
-    public synchronized SMPPSessionState getStateProcessor() {
-        return stateProcessor;
+    public SMPPSessionState getStateProcessor() {
+        stateProcessorLock.readLock().lock();
+        SMPPSessionState currentStateProcessor = stateProcessor;
+        stateProcessorLock.readLock().unlock();
+        return currentStateProcessor;
     }
 
-    public synchronized SessionState getSessionState() {
-        return stateProcessor.getSessionState();
+    public SessionState getSessionState() {
+        stateProcessorLock.readLock().lock();
+        SessionState sessionState = stateProcessor.getSessionState();
+        stateProcessorLock.readLock().unlock();
+        return sessionState;
     }
 
     @Override
     protected void changeState(SessionState newState) {
         if (!stateProcessor.getSessionState().equals(newState)) {
+            stateProcessorLock.writeLock().lock();
             final SessionState oldState = stateProcessor.getSessionState();
 
             // change the session state processor
@@ -58,6 +70,7 @@ protected void changeState(SessionState newState) {
             } else if (newState == SessionState.CLOSED) {
                 stateProcessor = SMPPSessionState.CLOSED;
             }
+            stateProcessorLock.writeLock().unlock();
             fireStateChanged(newState, oldState, smppSession);
         }
     }