import os
import pandas as pd
from threading import Lock

class UserID:
    def __init__(self): 
        self.lock = Lock()  
        self.counter = 0
        if os.path.exists('global_variable.csv'):
            df = pd.read_csv('global_variable.csv')
            self.counter = df['value'][0]
        
    def increment(self):
        with self.lock:
            self.counter += 1
            df = pd.DataFrame({'value': [self.counter]})
            df.to_csv('global_variable.csv', index=False)
            return self.counter