ProcessPoolExecutor documentation reports wrong exception being raised

[kahara]

BPO	34786
Nosy	@tirkarthi, @kahara
PRs	bpo-34786: Fix wrong exception reference: BrokenThreadPool -> BrokenProcessPool  #9533 [3.7] bpo-34786: Fix wrong exception reference: BrokenThreadPool -> BrokenProcessPool (GH-9533) #9554

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-09-25.03:38:07.732>
created_at = <Date 2018-09-24.12:32:16.067>
labels = ['3.7', '3.8', 'docs']
title = 'ProcessPoolExecutor documentation reports wrong exception being raised'
updated_at = <Date 2018-09-25.03:38:07.731>
user = 'https://github.com/kahara'

bugs.python.org fields:

activity = <Date 2018-09-25.03:38:07.731>
actor = 'xiang.zhang'
assignee = 'docs@python'
closed = True
closed_date = <Date 2018-09-25.03:38:07.732>
closer = 'xiang.zhang'
components = ['Documentation']
creation = <Date 2018-09-24.12:32:16.067>
creator = 'kahara'
dependencies = []
files = []
hgrepos = []
issue_num = 34786
keywords = ['patch']
message_count = 4.0
messages = ['326226', '326231', '326234', '326235']
nosy_count = 3.0
nosy_names = ['docs@python', 'xtreak', 'kahara']
pr_nums = ['9533', '9554']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue34786'
versions = ['Python 3.7', 'Python 3.8']

[kahara]

https://docs.python.org/3.8/library/concurrent.futures.html

"initializer is an optional callable that is called at the start of each worker process; initargs is a tuple of arguments passed to the initializer. Should initializer raise an exception, all currently pending jobs will raise a BrokenThreadPool, as well any attempt to submit more jobs to the pool."

This should be BrokenProcessPool?

[tirkarthi]

I think it raises BrokenThreadPool . A sample program that I tried as below raising an exception in the initializer. Maybe I am wrong here. Can you please attach a script that triggers BrokenProcessPool?

# bpo-34786.py

import concurrent.futures
import time

def bar(i):
    raise Exception(i) # Raise exception from the initializer

def foo(i):
    time.sleep(i)
    return "1"

with concurrent.futures.ThreadPoolExecutor(max_workers=5,
initializer=bar, initargs=(1,)) as executor:
future_to_url = {executor.submit(foo, i, 60): i for i in range(10)}
for future in concurrent.futures.as_completed(future_to_url):
try:
data = future.result()
except Exception as exc:
print('generated an exception: %s' % (exc))
else:
print('%d bytes' % (len(data)))

# Run the program

./python.exe ../backups/bpo34786.py
Exception in initializer:
Traceback (most recent call last):
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/concurrent/futures/thread.py", line 69, in _worker
    initializer(*initargs)
  File "../backups/bpo34786.py", line 5, in bar
    raise Exception(i)
Exception: 1
Exception in initializer:
Traceback (most recent call last):
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/concurrent/futures/thread.py", line 69, in _worker
    initializer(*initargs)
  File "../backups/bpo34786.py", line 5, in bar
    raise Exception(i)
Exception: 1
Traceback (most recent call last):
  File "../backups/bpo34786.py", line 13, in <module>
    future_to_url = {executor.submit(foo, i, 60): i for i in range(10)}
  File "../backups/bpo34786.py", line 13, in <dictcomp>
    future_to_url = {executor.submit(foo, i, 60): i for i in range(10)}
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/concurrent/futures/thread.py", line 148, in submit
    raise BrokenThreadPool(self._broken)
concurrent.futures.thread.BrokenThreadPool: A thread initializer failed, the thread pool is not usable anymore

Thanks

[kahara]

Perhaps I wasn't clear that this considered ProcessPoolExecutor documentation, not ThreadPoolExecutor. Taking the example from documentation and adding an initializer like this:

import concurrent.futures
import math

PRIMES = [
    112272535095293,
    112582705942171,
    112272535095293,
    115280095190773,
    115797848077099,
    1099726899285419]

def is_prime(n):
    if n % 2 == 0:
        return False

    sqrt_n = int(math.floor(math.sqrt(n)))
    for i in range(3, sqrt_n + 1, 2):
        if n % i == 0:
            return False
    return True

def init():
    raise Exception()

def main():
    with concurrent.futures.ProcessPoolExecutor(initializer=init) as executor:
        for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)):
            print('%d is prime: %s' % (number, prime))

if __name__ == '__main__':
    main()

...yields the following:

Exception in initializer:
Traceback (most recent call last):
  File "/Users/developer/cpython/Lib/concurrent/futures/process.py", line 219, in _process_worker
    initializer(*initargs)
  File "/tmp/bpo34786.py", line 25, in init
    raise Exception()
Exception
Exception in initializer:
Traceback (most recent call last):
  File "/Users/developer/cpython/Lib/concurrent/futures/process.py", line 219, in _process_worker
    initializer(*initargs)
  File "/tmp/bpo34786.py", line 25, in init
    raise Exception()
Exception
Exception in initializer:
Traceback (most recent call last):
  File "/Users/developer/cpython/Lib/concurrent/futures/process.py", line 219, in _process_worker
    initializer(*initargs)
  File "/tmp/bpo34786.py", line 25, in init
    raise Exception()
Exception
Exception in initializer:
Traceback (most recent call last):
  File "/Users/developer/cpython/Lib/concurrent/futures/process.py", line 219, in _process_worker
    initializer(*initargs)
  File "/tmp/bpo34786.py", line 25, in init
    raise Exception()
Exception
Traceback (most recent call last):
  File "/tmp/bpo34786.py", line 33, in <module>
    main()
  File "/tmp/bpo34786.py", line 29, in main
    for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)):
  File "/Users/developer/cpython/Lib/concurrent/futures/process.py", line 476, in _chain_from_iterable_of_lists
    for element in iterable:
  File "/Users/developer/cpython/Lib/concurrent/futures/_base.py", line 594, in result_iterator
    yield fs.pop().result()
  File "/Users/developer/cpython/Lib/concurrent/futures/_base.py", line 436, in result
    return self.__get_result()
  File "/Users/developer/cpython/Lib/concurrent/futures/_base.py", line 388, in __get_result
    raise self._exception
concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while the future was running or pending.

[tirkarthi]

Got it. Sorry about that I copy pasted the quoted string and assumed ThreadPoolExecutor overlooking the PR. The change is reasonable to me.

Thanks