How to run non-deamon pool

[Borda]

Hello, I am wondering if there is an option how to run non-daemon processing pool within pathos. My goal is to run a processing pool within another processing work. I have found a couple of tricks for standard multiprocessing package but none of them works for pathos...

• https://stackoverflow.com/a/8963618/4521646
• http://mindcache.me/2015/08/09/python-multiprocessing-module-daemonic-processes-are-not-allowed-to-have-children.html

from pathos.helpers import mp
class NoDaemonProcess(mp.Process):
    # make 'daemon' attribute always return False
    def _get_daemon(self):
        return False
    def _set_daemon(self, value):
        pass
    daemon = property(_get_daemon, _set_daemon)

from pathos.multiprocessing import ProcessPool
class NoDaemonProcessPool(ProcessPool):
    Process = NoDaemonProcess

where instead of multiprocessing.pool.Pool I am using pathos.multiprocessing.ProcessPool and the error message is

  File ".../experiments.py", line 390, in iterate_map_parallel
    for out in mapping(wrap_func, iterate_vals):
  File "/home/jb/.local/lib/python3.6/site-packages/multiprocess/pool.py", line 735, in next
    raise value
AssertionError: daemonic processes are not allowed to have children

[mmckerns]

Sorry for the slow response. pathos pools are wrappers around multiprocess pools. Have you tried using pathos.multiprocessing.Pool? That's the raw multiprocess.Pool object without the pathos interface wrapper.

[Borda]

I played with it for a while and I believe that I tried this too, but it ended the same... :(

[mmckerns]

I tried your code, both using ProcessPool and Pool from pathos.multiprocessing and I don't receive an error.

from pathos.helpers import mp
class NoDaemonProcess(mp.Process):
    # make 'daemon' attribute always return False
    def _get_daemon(self):
        return False
    def _set_daemon(self, value):
        pass
    daemon = property(_get_daemon, _set_daemon)

from pathos.multiprocessing import ProcessPool
class NoDaemonProcessPool(ProcessPool):
    Process = NoDaemonProcess


if __name__ == '__main__':
    p = NoDaemonProcessPool()
    x = ProcessPool().map(lambda x:x, p.map(lambda x:x, range(4)))
    print(x)

Is this not what you intended to do?
It works for me in all versions of python I have, using the most recent development versions of dill, multiprocess, and pathos.

[mmckerns]

Also works in the interpreter (only tested 2.7, as opposed to all versions above)

Python 2.7.16 (default, Apr  1 2019, 14:50:56) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from pathos.helpers import mp
>>> class NoDaemonProcess(mp.Process):
...     # make 'daemon' attribute always return False
...     def _get_daemon(self):
...         return False
...     def _set_daemon(self, value):
...         pass
...     daemon = property(_get_daemon, _set_daemon)
... 
>>> from pathos.multiprocessing import ProcessPool
>>> class NoDaemonProcessPool(ProcessPool):
...     Process = NoDaemonProcess
... 
>>> p = NoDaemonProcessPool()
>>> ProcessPool().map(lambda x:x, p.map(lambda x:x, range(4)))
[0, 1, 2, 3]
>>> 

[Borda]

@mmckerns it seems that your examples run fine, but somehow it crashes in my codes...
Using your classes I have defined my class with some parallel processing:

class Cls(object):
    """Sample

    >>> Cls().parallel()
    """
    vals = range(5)
    def _sum(self, nb):
        return NoDaemonProcessPool(2).map(sum, [self.vals] * nb)
    def parallel(self):
        return NoDaemonProcessPool(2).map(self._sum, range(10))

crashes with following

Traceback (most recent call last):
      File "/home/jb/Applications/PyCharm-2019/helpers/pycharm/docrunner.py", line 140, in __run
        compileflags, 1), test.globs)
      File "<doctest Cls[0]>", line 1, in <module>
        Cls().parallel()
      File ".../experiments.py", line 500, in parallel
        return NoDaemonProcessPool(2).map(self._sum, range(10))
      File "/home/jb/.local/lib/python3.6/site-packages/pathos/multiprocessing.py", line 137, in map
        return _pool.map(star(f), zip(*args)) # chunksize
      File "/home/jb/.local/lib/python3.6/site-packages/multiprocess/pool.py", line 266, in map
        return self._map_async(func, iterable, mapstar, chunksize).get()
      File "/home/jb/.local/lib/python3.6/site-packages/multiprocess/pool.py", line 644, in get
        raise self._value
    AssertionError: daemonic processes are not allowed to have children

I believe now that the problem is in my integrating to a class calling own method...

[Borda]

it runs locally fine but executing your examples on CI it fails for both py2 and py3
https://circleci.com/gh/Borda/BIRL/1417
https://circleci.com/gh/Borda/BIRL/1418

[mmckerns]

@Borda: Not sure what's going on with your tests... but the failures in the two links above are potentially due to other issues...

1417: UNEXPECTED EXCEPTION: TypeError("cannot serialize '_io.FileIO' object",)
1418: UNEXPECTED EXCEPTION: TypeError("'NoneType' object is not callable",)