The document discusses asynchronous programming in JavaScript and Python, explaining concepts like the call stack, callbacks, and how asynchronous code execution operates. It includes code examples to illustrate these concepts and highlights the differences between asynchronous execution and multithreading. The main takeaway is that asynchronous programming is single-threaded and heavy tasks can block the event loop.

1. Asynchronous
programming
JS and python inside
Maxim Schepelin

3. Contents
● Python.
● What is call stack?
● Where callbacks come from?
● How asynchronous code execution works?
● Summary

4. Code: Call stack:
def multiply(x, y):
return x * y
def square(x):
return multiply(x, x)
def print_result(n):
result = square(n)
sys.stdout.write(result)
if __name__ == '__main__':
print_result(4)
multiply
square
print_result
main

5. Code: Call stack:
def foo():
foo()
if __name__ == '__main__':
foo()
foo
foo
foo
foo
foo
foo
foo
main
RuntimeError: maximum recursion depth exceeded

6. Contents
● Python.
● What is call stack?
● Where callbacks come from?
● How asynchronous code execution works?
● Summary

7. Code: Call stack:
console.log(1);
console.log(2);
setTimeout(function ( ) {
console.log(4);
}, 500);
console.log(3);
csoentTsiomlee.olougt
anonymous main
func

8. Code: Call stack:
console.log(1);
console.log(2);
setTimeout(function ( ) {
console.log(4);
}, 500);
console.log(3);
csoentTsiomlee.olougt
anonymous main
func
Browser engine:
Timer(cb)
Callback queue: callback
1
2
3

9. Contents
● Python.
● What is call stack?
● Where callbacks come from?
● How asynchronous code execution works?
● Summary

11. Asynchronous workflow
Call stack
Event-loop Async call
External API
Callback
queue

12. Code: Call stack:
console.log(1);
console.log(2);
setTimeout(function ( ) {
console.log(4);
}, 0);
console.log(3);
csoentTsiomlee.olougt
anonymous main
func
Browser engine:
Timer(cb)
Callback queue: callback
1
2
3

13. Callbacks are invoked
only when call stack is
emtpy!

14. Contents
● Python.
● What is call stack?
● Where callbacks come from?
● How asynchronous code execution works?
● Summary

15. Summary
● Asynchromous != multithreading
● Heavy things blocks the event-loop
● It’s still single thread

16. Q&A
schepelin
Maxim Schepelin