Descrição do Problema
Eu ajustei o código deesta resposta um pouco (veja abaixo). No entanto, ao executar este script no Linux (então linha de comando:python script_name.py) será impressojobs running: x para todos os trabalhos, mas depois parece que ficou preso depois disso. No entanto, quando eu uso o método de desova (mp.set_start_method('spawn')) funciona bem e começa imediatamente a imprimir o valor dacounter variável (consultelistener método).

Pergunta, questão

Por que funciona apenas quando processos de desova?Como posso ajustar o código para que ele funcione comfork? (porque provavelmente é mais rápido)

Código

import io
import csv
import multiprocessing as mp

NEWLINE = '\n'

def file_searcher(file_path):
    parsed_file = csv.DictReader(io.open(file_path, 'r', encoding='utf-8'), delimiter='\t')

    manager = mp.Manager()
    q = manager.Queue()
    pool = mp.Pool(mp.cpu_count())

    # put listener to work first
    watcher = pool.apply_async(listener, (q,))

    jobs = []
    for row in parsed_file:
        print('jobs running: ' + str(len(jobs) + 1))
        job = pool.apply_async(worker, (row, q))
        jobs.append(job)

  # collect results from the workers through the pool result queue
    for job in jobs:
        job.get()

    #now we are done, kill the listener
    q.put('kill')
    pool.close()
    pool.join()

def worker(genome_row, q):
    complete_data = []
    #data processing
    #ftp connection to retrieve data
    #etc.
    q.put(complete_data)
    return complete_data

def listener(q):
    '''listens for messages on the q, writes to file. '''
    f = io.open('output.txt', 'w', encoding='utf-8')
    counter = 0
    while 1:
        m = q.get()
        counter +=1
        print(counter)
        if m == 'kill':
            break
        for x in m:
            f.write(x + NEWLINE)
        f.flush()
    f.close()

if __name__ == "__main__":
   file_searcher('path_to_some_tab_del_file.txt')

Informações do processador

Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                20
On-line CPU(s) list:   0-19
Thread(s) per core:    1
Core(s) per socket:    1
Socket(s):             20
NUMA node(s):          2
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 45
Model name:            Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz
Stepping:              2
CPU MHz:               2596.501
BogoMIPS:              5193.98
Hypervisor vendor:     VMware
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              25600K
NUMA node0 CPU(s):     0-19

Versão do kernel do Linux

3.10.0-514.26.2.el7.x86_64

Versão Python

Python 3.6.1 :: Continuum Analytics, Inc.

REGISTRO
Eu adicionei o código conforme sugerido por @yacc, isso fornecerá o seguinte log:

[server scripts]$ python main_v3.py
[INFO/SyncManager-1] child process calling self.run()
[INFO/SyncManager-1] created temp directory /tmp/pymp-2a9stjh6
[INFO/SyncManager-1] manager serving at '/tmp/pymp-2a9stjh6/listener-jxwseclw'
[DEBUG/MainProcess] requesting creation of a shared 'Queue' object
[DEBUG/SyncManager-1] 'Queue' callable returned object with id '7f0842da56a0'
[DEBUG/MainProcess] INCREF '7f0842da56a0'
[DEBUG/MainProcess] created semlock with handle 139673691570176
[DEBUG/MainProcess] created semlock with handle 139673691566080
[DEBUG/MainProcess] created semlock with handle 139673691561984
[DEBUG/MainProcess] created semlock with handle 139673691557888
[DEBUG/MainProcess] added worker
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-2] INCREF '7f0842da56a0'
[DEBUG/MainProcess] added worker
[INFO/ForkPoolWorker-2] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-4] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-4] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-3] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-3] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-6] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-5] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-6] child process calling self.run()
[INFO/ForkPoolWorker-5] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-7] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-8] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-7] child process calling self.run()
[INFO/ForkPoolWorker-8] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-9] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-9] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-10] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-10] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-11] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-11] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-12] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-12] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-13] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-13] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-14] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-14] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-15] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-15] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-16] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-16] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-17] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-17] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-18] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-18] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-19] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-19] child process calling self.run()
[DEBUG/MainProcess] added worker
[DEBUG/ForkPoolWorker-20] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-20] child process calling self.run()
jobs running: 1
jobs running: 2
jobs running: 3
jobs running: 4
[DEBUG/ForkPoolWorker-21] INCREF '7f0842da56a0'
[INFO/ForkPoolWorker-21] child process calling self.run()
jobs running: 5
jobs running: 6
jobs running: 7
[DEBUG/ForkPoolWorker-2] INCREF '7f0842da56a0'
jobs running: 8
written to file
jobs running: 9
jobs running: 10
[DEBUG/ForkPoolWorker-2] thread 'MainThread' does not own a connection
[DEBUG/ForkPoolWorker-2] making connection to manager
jobs running: 11
jobs running: 12
jobs running: 13
jobs running: 14
jobs running: 15
[DEBUG/SyncManager-1] starting server thread to service 'ForkPoolWorker-2'
jobs running: 16
jobs running: 17
jobs running: 18
jobs running: 19
[DEBUG/ForkPoolWorker-4] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-3] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-5] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-6] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-7] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-8] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-10] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-9] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-11] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-13] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-14] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-12] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-15] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-16] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-18] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-17] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-20] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-19] INCREF '7f0842da56a0'
[DEBUG/ForkPoolWorker-21] INCREF '7f0842da56a0'