Multi Threading in NLTK WordNetLemmatizer?

I am trying to use multi threading to speed up the process. I am using the wordnetlemmatizer to lemmatize the words and those words can be further used by sentiwordnet to calculate the sentiment of the text. My Sentiment analysis function where I am using the WordNetLemmatizer is as follows:

import nltk
from nltk.corpus import sentiwordnet as swn

def SentimentA(doc, file_path):
    sentences = nltk.sent_tokenize(doc)
    # print(sentences)
    stokens = [nltk.word_tokenize(sent) for sent in sentences]
    taggedlist = []
    for stoken in stokens:
        taggedlist.append(nltk.pos_tag(stoken))
    wnl = nltk.WordNetLemmatizer()
    score_list = []
    for idx, taggedsent in enumerate(taggedlist):
        score_list.append([])
        for idx2, t in enumerate(taggedsent):
            newtag = ''
            lemmatized = wnl.lemmatize(t[0])
            if t[1].startswith('NN'):
                newtag = 'n'
            elif t[1].startswith('JJ'):
                newtag = 'a'
            elif t[1].startswith('V'):
                newtag = 'v'
            elif t[1].startswith('R'):
                newtag = 'r'
            else:
                newtag = ''
            if (newtag != ''):
                synsets = list(swn.senti_synsets(lemmatized, newtag))

                score = 0
                if (len(synsets) > 0):
                    for syn in synsets:
                        score += syn.pos_score() - syn.neg_score()
                    score_list[idx].append(score / len(synsets))
    return SentiCal(score_list)

After running 4 threads, I am getting the following error for the first 3 threads and the last thread is working perfectly.

AttributeError: 'WordNetCorpusReader' object has no attribute '_LazyCorpusLoader__args'

I have already tried importing the NLTK package locally as given in this NLTK issue and tried the solution given on this page.

Quick hack:

import nltk
from nltk.corpus import sentiwordnet as swn
# Do this first, that'll do something eval() 
# to "materialize" the LazyCorpusLoader
next(swn.all_senti_synsets()) 

# Your other code here.

More details later... Still typing