Is Opencv dnn module thread-safe

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I want to deploy an image classification application with opencv dnn module. here's some logic code:

inputBlob = cv::dnn::blobFromImage(img); 
this->caffeNet.setInput(inputBlob, "data");
probMat = this->caffeNet.forward("prob").reshape(1, 1); 
cv::minMaxLoc(probMat, NULL, NULL, NULL, &classNumber);

if it's not thread-safe, where should I add lock?? like this?

mtx.lock();
probMat = this->caffeNet.forward("prob").reshape(1, 1); 
mtx.unlock();