diff --git a/.travis.yml b/.travis.yml
index f8f21e0..4603f2d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,7 +14,10 @@ before_install:
 - pip install pytest-cov
 
 install:
-- pip install -r requirements.txt
+- if [ $TRAVIS_PYTHON_VERSION == 3.8 ]; 
+  then pip install -r gklearn/tests/requirements.txt;
+  else pip install -r requirements.txt;
+  fi
 - pip install wheel
 
 script:
diff --git a/gklearn/tests/requirements.txt b/gklearn/tests/requirements.txt
index a48620b..d0aa596 100644
--- a/gklearn/tests/requirements.txt
+++ b/gklearn/tests/requirements.txt
@@ -1,7 +1,7 @@
-numpy==1.15.2
-scipy==1.1.0
-matplotlib==3.0.0
-networkx==2.2
-scikit-learn==0.20.0
-tabulate==0.8.2
-tqdm==4.26.0
+numpy
+scipy
+matplotlib
+networkx
+scikit-learn
+tabulate
+tqdm
diff --git a/gklearn/utils/ipython_log.py b/gklearn/utils/ipython_log.py
deleted file mode 100644
index 9574d84..0000000
--- a/gklearn/utils/ipython_log.py
+++ /dev/null
@@ -1,7 +0,0 @@
-# IPython log file
-
-runfile('/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage/test_iam.py', wdir='/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage')
-runfile('/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage/test_iam.py', wdir='/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage')
-runfile('/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage/test_iam.py', wdir='/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage')
-runfile('/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage/test_iam.py', wdir='/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage')
-runfile('/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage/test_iam.py', wdir='/media/ljia/DATA/research-repo/codes/Linlin/py-graph/preimage')
diff --git a/gklearn/utils/parallel.py b/gklearn/utils/parallel.py
index 603164a..46e9217 100644
--- a/gklearn/utils/parallel.py
+++ b/gklearn/utils/parallel.py
@@ -33,6 +33,8 @@ def parallel_me(func, func_assign, var_to_assign, itr, len_itr=None, init_worker
                     desc=itr_desc, file=sys.stdout) if verbose else 
                     pool.imap_unordered(func, itr, chunksize)):
                     func_assign(result, var_to_assign)
+            pool.close()
+            pool.join()
         else:
             if n_jobs == None:
                 n_jobs = multiprocessing.cpu_count()
@@ -46,7 +48,8 @@ def parallel_me(func, func_assign, var_to_assign, itr, len_itr=None, init_worker
                     desc=itr_desc, file=sys.stdout) if verbose else 
                     pool.imap_unordered(func, itr, chunksize)):
                     func_assign(result, var_to_assign)
-            
+            pool.close()
+            pool.join()
                     
 
 def parallel_gm(func, Kmatrix, Gn, init_worker=None, glbv=None,