New submission from gaoxinge <[email protected]>:
## abstract
When using concurrent.futures.ThreadPoolExecutor module, if we code pool.submit
in callback, the callback may be not run. This is because main thread will
terminate, and call _python_exit to add none to _work_queue before subthread
run callback.
## code
```
# -*- coding: utf-8 -*-
from concurrent.futures import ThreadPoolExecutor
def func(x, y):
import time
time.sleep(1)
return x + y
def do_many(n):
def callback(fut):
nonlocal n
result = fut.result()
print('Got: ', result)
n -= 1
if n > 0:
future = pool.submit(func, n, n)
future.add_done_callback(callback)
if n > 0:
future = pool.submit(func, n, n)
future.add_done_callback(callback)
# _python_exit will be called here, and then
# add none to _work_queue
pool = ThreadPoolExecutor(max_workers=8)
do_many(10)
```
## result and expectation
The code's result may be
```
Got: 20
Got: 18
Got: 16
Got: 14
Got: 12
Got: 10
Got: 8
Got: 6
```
But my expectation is
```
Got: 20
Got: 18
Got: 16
Got: 14
Got: 12
Got: 10
Got: 8
Got: 6
Got: 4
Got: 2
```
## question
Is my expectation reasonable?
### if not reasonable
If not, my solution is
```
from concurrent.futures import ThreadPoolExecutor
def func(x, y):
import time
time.sleep(1)
return x + y
def do_many():
def callback(fut):
global n
result = fut.result()
print('Got: ', result)
n -= 1
if n > 0:
future = pool.submit(func, n, n)
future.add_done_callback(callback)
if n > 0:
future = pool.submit(func, n, n)
future.add_done_callback(callback)
n = 10
pool = ThreadPoolExecutor(max_workers=8)
do_many()
while n > 0: # use while to block main thread
pass
```
and is there any elegant solution?
### if reasonable
...
----------
components: Library (Lib)
messages: 322605
nosy: gaoxinge
priority: normal
severity: normal
status: open
title: run pool.submit in callback when future.set_result
type: behavior
versions: Python 3.6
_______________________________________
Python tracker <[email protected]>
<https://bugs.python.org/issue34268>
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