Is callback function is thread safe?

[Nihanth Joseph]

I have written playbooks to manage 100s of machines and i am using callback plugins to capture the output of each task and generate reports at the end. Since I am using forks (eg. 20) do i have to handle each output in thread safe manner? 

eg:

class CallbackModule(CallbackBase):    

    def __init__(self):

         output = []

    def v2_runner_on_ok(self, result, **kwargs):

        with self.lock:

             # capture output

    def v2_playbook_on_stats(self, stats):

        # generate report