How to run Selenium python test simultaneously on single Instance of browser

Initially I was using new instance of browser for each test. But chrome process created a lot of orphan processes , which piled up over time and hogged the server on cpu cycles and memory so to avoid this, I have defined driver as global variable and was passing it to different tests. But the problem with code is if tests run sequentially it works fine, not able to run multiple tests simultaneously on single instance of browser.

driver = ""

def getChromeDriver():
    global driver
    options = Options()
    options.add_argument("--headless")
    options.add_argument("--no-sandbox")
    options.add_argument("window-size=1200,1100")
    driver = webdriver.Chrome(chrome_options=options, executable_path='my/path')

tests:

def testGoogle():
    driver.get(www.google.com)

def testyahoo():
    driver.get(www.yahoo.com)