MultiThreading in AWS lambda using Python3

Question

I am trying to implement Multithreading in AWS lambda. This is a Sample code that defines the format of my original code which I am trying to execute in lambda.

import threading
import time

def this_will_await(arg,arg2):
  print("Hello User")
  print(arg,arg2)

def this_should_start_then_wait():
  print("This starts")
  timer = threading.Timer(3.0, this_will_await,["b","a"])
  timer.start()
  print("This should execute")

this_should_start_then_wait()

In my local Machine, this code is working fine. The output I am receiving is:

This starts
This should execute
.
.
.
Hello User
('b', 'a')

Those 3 . represents that it waited for 3 seconds to complete the execution.

Now when I execute the same thing in AWS lambda. I am only receiving

This starts
This should execute

I think it's not calling the this_will_await() function.

Answer 1

Have you tried adding timer.join()? You'll need to join the Timer thread because otherwise the Lambda environment will kill off the thread when the parent thread finishes.

This code in a Lambda function:

import threading
import time

def this_will_await(arg,arg2):
  print("Hello User")
  print(arg,arg2)

def this_should_start_then_wait():
  print("This starts")
  timer = threading.Timer(3.0, this_will_await,["b","a"])
  timer.start()
  timer.join()
  print("This should execute")

this_should_start_then_wait()

def lambda_handler(event, context):
    return this_should_start_then_wait()

Produces this output:

This starts
Hello User
b a
This should execute