problems in using learnlib API refineHypothesis()

[IMhappyZzz]

Hi，
I just use the tool to test some other protocols , I modified the SUL and used TLSTestService.java to fit new protocol , and the test passed. But when I used learner.java to learn its statemachine , it runed but always got stuck .the console showed like this: "INFO: Starting round XX", while the process did not stoped. as a result ,I can't learned the final hypothesis.

after some tests ,i found maybe it got something wrong in learnner.java with using the API refineHypothesis(),

learn()
{
boolean learning= true;
learningAlgorithm.startLearning();
hypothesis = learningAlgorithm.getHypothesisModel();
while(learning)
{
counterExample = equivalenceAlgorithm.findCounterExample();
if(counterExample == null) {
learning= false;
}
else{
result= learningAlgorithm.refineHypothesis(counterExample);
hypothesis = learningAlgorithm.getHypothesisModel();
}

......get the final HypothesisModel.............
}

it always hung up in refineHypothesis(), then i will get someHypothesis but not the final result.
i test the tools in VMware ,ubuntu16.04, i can't find out what's wrong with it , is the jvm's heap used out ?

Thanks!