README.md

thredo

Thredo is threads on async. For the brave. Or the foolish. Only time will tell.

High Level Overview (The Big Idea)

Consider the following thread program involving a worker, a producer, and queue::

import threading
import queue
import time

def worker(q):
    while True:
        item = q.get()
        if item is None:
            break
        print('Got:', item)

def main():
    q = queue.Queue()
    t = threading.Thread(target=worker, args=(q,))
    t.start()
    for n in range(10):
        q.put(n)
        time.sleep(1)
    q.put(None)
    t.join()

main()

In this code, there are blocking operations such as q.get() and time.sleep(). This blocking is ultimately handled by the host operating system. Because of that, it is very difficult for Python to do anything related to the actual control or scheduling of threads. Once blocked, a thread stays blocked forever or until some event occurs that causes it to unblock.

Thredo re-envisions threads by redirecting all blocking operations to an async library. The code looks mostly the same except that you use the thredo module. For example:

import thredo

def worker(q):
    while True:
        item = q.get()
        if item is None:
            break
        print('Got:', item)

def main():
    q = thredo.Queue()
    t = thredo.spawn(worker, q)
    for n in range(10):
        q.put(n)
        thredo.sleep(1)
    q.put(None)
    t.join()

thredo.run(main)

The main reason you'd use thredo however is that it gives you extra features such as thread groups, cancellation, and more. For example, here's a more advanced version of the above code::

import thredo

def worker(q):
    try:
        while True:
            item = q.get()
            print('Got:', item)
            q.task_done()
    except thredo.ThreadCancelled:
        print('Worker cancelled')

def main():
    q = thredo.Queue()
    with thredo.ThreadGroup(wait=None) as workers:
        for n in range(4):
            workers.spawn(worker, q)

        for n in range(10):
            q.put(n)
            thredo.sleep(1)

        workers.join()    

thredo.run(main)

Examples

The examples directory contains more examples of using thredo. The examples/euro directory contains coding samples from the EuroPython 2018 talk.