On 2024-03-22 12:08 PM, Thomas Nyberg via Python-list wrote:
Hi,
Yeah so flask does support async (when installed with `pip3 install
flask[async]), but you are making a good point that flask in this case
is a distraction. Here's an example using just the standard library that
exhibits the same issue:
`app.py`
```
import asyncio
import threading
import time
from queue import Queue
in_queue = Queue()
out_queue = Queue()
def worker():
print("worker started running")
while True:
future = in_queue.get()
print(f"worker got future: {future}")
time.sleep(5)
print("worker sleeped")
out_queue.put(future)
def finalizer():
print("finalizer started running")
while True:
future = out_queue.get()
print(f"finalizer got future: {future}")
future.set_result("completed")
print("finalizer set result")
threading.Thread(target=worker).start()
threading.Thread(target=finalizer).start()
async def main():
future = asyncio.get_event_loop().create_future()
in_queue.put(future)
print(f"main put future: {future}")
result = await future
print(result)
if __name__ == "__main__":
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
```
If I run that I see the following printed out (after which is just hangs):
```
Combining Dieter's and Mark's ideas, here is a version that works.
It is not pretty! call_soon_threadsafe() is a loop function, but the
loop is not accessible from a different thread. Therefore I include a
reference to the loop in the message passed to in_queue, which in turn
passes it to out_queue.
Frank
=======================================================
import asyncio
import threading
import time
from queue import Queue
in_queue = Queue()
out_queue = Queue()
def worker():
print("worker started running")
while True:
loop, future = in_queue.get()
print(f"worker got future: {future}")
time.sleep(5)
print("worker sleeped")
out_queue.put((loop, future))
def finalizer():
print("finalizer started running")
while True:
loop, future = out_queue.get()
print(f"finalizer got future: {future}")
loop.call_soon_threadsafe(future.set_result, "completed")
print("finalizer set result")
threading.Thread(target=worker, daemon=True).start()
threading.Thread(target=finalizer, daemon=True).start()
async def main():
loop = asyncio.get_event_loop()
future = loop.create_future()
in_queue.put((loop, future))
print(f"main put future: {future}")
result = await future
print(result)
if __name__ == "__main__":
# loop = asyncio.get_event_loop()
# loop.run_until_complete(main())
asyncio.run(main())
--
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