JDK 1.7 - Java Application Blocking

I use JDK 1.7.

My java application is blocking from time to time. I have added some log lines and now I know exactly where is blocking, but I have no solution to fix it.
 
This code runs in a parallel thread, distinct from the main application thread and updates a big JTextArea swing:

try {
....
    JTextArea element = (JTextArea)add_containers[objColIndex];
    System.out.println("setEditValue start seting text ");
    element.setText(VAL);
    System.out.println("setEditValue text is set ");

[Code] ....

The code reaches "setEditValue start seting tex" but never reaches "setEditValue text is set". No exception is triggered. The whole application is blocked - main thread and this paralel thread. This section of code is called many times, but in rare cases is blocking without any apparent reason. Sometimes I run the exact same instructions and is blocking and sometimes is working.