python - Why does my context manager __exit__ function run before the computation isn't finished? -

the exit function of custom context manager seemingly runs before computation done. context manager meant simplify writing concurrent/parallel code. here context manager code:

import time multiprocessing.dummy import pool, cpu_count  class managed_pool:     '''simple context manager multiprocessing.dummy.pool'''     def __init__(self, msg):         self.msg = msg     def __enter__(self):         cores = cpu_count()         print 'start concurrent ({0} cores): {1}'.format(cores, self.msg)         self.start = time.time()         self.pool = pool(cores)         return self.pool     def __exit__(self, type_, value, traceback):         print 'end concurrent:', self.msg         print 'time:', time.time() - self.start         self.pool.close()         self.pool.join() 

i've tried script multiprocessing.pool instead of multiprocessing.dummy.pool , seems fail time.

here example of using context manager:

def read_engine_files(f):     engine_input = engineinput()     open(f, 'rb') f:         engine_input.parse_from_string(f.read())     return engine_input  managed_pool('load input files') pool:     data = pool.map(read_engine_files, files) 

so, inside of read_engine_files print name of file. you'll notice in __exit__ function print out when computation done , how long took. when viewing stdout __exit__ message appears way before computation finished. like, minutes before computation done. htop says of cores still being used. here's example of output

start concurrent (4 cores): load engine input files file1.pbin file2.pbin ... file16.pbin end concurrent: load engine input files time: 246.43829298 file17.pbin ... file45.pbin 

why __exit__ being called early?

are sure you're calling pool.map()? should block until items have been mapped.

if you're calling 1 of asynchronous methods of pool, should able solve problem changing order of things in __exit__(). join pool before doing summary.

def __exit__(self, type_, value, traceback):     self.pool.close()     self.pool.join()     print 'end concurrent:', self.msg     print 'time:', time.time() - self.start