Thredo is threads on async. For the brave. Or the foolish. Only time will tell.
Note: Thredo requires the most up-to-date version of Curio--meaning the one that is checked out of the Curio GitHub repository at https://github.com/dabeaz/curio.
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)
The examples directory contains more examples of using thredo.
The examples/euro directory contains coding samples from the
EuroPython 2018 talk.
Q: Is this going to turn into a full-fledged project?
A: It's too early to say.
Q: Isn't this sort of like using concurrent.futures?
A: No. concurrent.futures provides no mechanism for controlling threads and no mechanism for cancelling threads. Although it might appear like this is so, given that you can seemingly "cancel" a Future, this has no effect on thread execution. Once started, worked submitted to a thread pool in concurrent.futures runs to completion regardless of whether or not the associated Future is cancelled. Cancelling a future really only causes it to be abandoned if it hasn't yet started. If you cancel a thread in thredo, it is cleanly cancelled at the next blocking operation.