use sklearn cross validation train, in PyQt button

Question

I want to to create GUI to choose data set file with QFileDialge and lanche the training of SVM with this data set using cross validation method.

The cross validation takes a lot a time when data is large and the GUI will crash. For that reason I use QThread for training. However when i set the number of job -1 to use all cores of my CPU sklearn returns the following warning and only uses 1 core.

\anaconda\lib\site-packages\sklearn\externals\joblib\parallel.py:547: UserWarning: Multiprocessing-backed parallel loops cannot be nested below threads, setting n_jobs=1 **self._backend_args)

from PyQt5.Qt import QThread
from sklearn.model_selection import cross_val_score
from sklearn import svm


class train(QThread):
    def __init__(self,data,class_):
        super().__init__()
        self.data = data
        self.cls = class_
    def run(self):
        self.score = cross_val_score(estimator=svm.SVC(), # smv
                                       X=self.ata, y=self.cls, # data
                                       cv=10, # number of partition
                                       n_jobs=-1) # all the cores in cpu