Async/Await examples

README.md

This is a comparison of the different async/await strategies.

Python is the only language that doesn't execute the coroutines/tasks until you await for them.

test-fixed.py

# This program runs like the JS one (is the "fixed" version of the one with async/await syntax)
from asyncio import get_event_loop, ensure_future, coroutine


@coroutine
def third():
    print("third")
    yield
    return 3

@coroutine
def second():
    print("second")
    call = third()
    next(call)
    print("third:called")
    yield
    result = yield from call
    print("third:finished", result)
    return 2


@coroutine
def first():
    print("first")
    call = second()
    next(call)
    print("second:called")
    result = yield from call
    print("second:finished", result)
    return 1


async def main():
    await first()


loop = get_event_loop()
loop.run_until_complete(main())
loop.close()

# This will output:

# first
# second
# third
# third:called
# second:called
# third:finished 3
# second:finished 2

test.cs

using System;
using System.Threading.Tasks;

class Program
{
    public static void Main()
    {
        // Start the HandleFile method.
        Task<int> task = first();
    }

    static async Task<int> third()
    {
        Console.WriteLine("third");
        return 3;
    }

    static async Task<int> second()
    {
        Console.WriteLine("second");
        Task<int> task = third();
        Console.WriteLine("third:called");
        int result = await task;
        Console.WriteLine("third:awaited " + result);
        return 2;
    }

    static async Task<int> first()
    {
        Console.WriteLine("first");
        Task<int> task = second();
        Console.WriteLine("second:called");
        int result = await task;
        Console.WriteLine("second:awaited " + result);
        return 1;
    }
}

// Will output the following:

// first
// second
// third
// third:called
// third:awaited 3
// second:called
// second:awaited 2

test.js

async function third() {
  console.log("third");
  return 3;
}

async function second() {
  console.log("second");
  let call = third();
  console.log("third:called");
  let result = await call;
  console.log("third:awaited", result);
  return 2;
}

async function first() {
  console.log("first");
  let s = second();
  console.log("second:called");
  let result = await s;
  console.log("second:awaited", result);
}

first().then();

// Will output the following:

// first
// second
// third
// third:called
// second:called
// third:awaited 3
// second:awaited 2

test.py

from asyncio import get_event_loop


async def third():
    print("third")
    return 3

async def second():
    print("second")
    call = third()
    print("third:called")
    result = await call
    print("third:awaited", result)
    return 1


async def first():
    print("first")
    call = second()
    print("second:called")
    result = await call
    print("second:awaited", result)
    return 1

async def main():
    await first()


loop = get_event_loop()
loop.run_until_complete(main())
loop.close()

# Will output the following:

# first
# second:called
# second
# third:called
# third
# third:awaited 3
# second:awaited 1