import multiprocessing as mp
import multiprocessing.managers as mmp
import os, sys
import psutil
import traceback

sout = sys.stdout

def processes():
    """ Print list of pid and child pids if any """
    pid = os.getpid()
    pr = psutil.Process(pid)
    # First is always the current process
    pids = [pid] + pr.children()
    sout.write("Process IDs => " + str(pids) + "\n")

# Create a base manager
bm = mmp.BaseManager(('', 50000))
# Single process
processes()

# Now start the manager's subprocess
bm.start()
# Two processes - expected
processes()
# Shut it down
bm.shutdown()
# Back to single process
processes()

# Now create a syncmanager
sm = mp.Manager()
print type(sm)

# Hmmm - two processes ?
# SyncManager starts its own process without a call to start - this is undocumented
processes()
try:
    sout.write('Trying to start syncmanager ...\n')
    # This gets even more odd
    sm.start()
except AssertionError as e:
    # raise
    # An assertion error is raised as apparently you can't start a SyncManager
    # without intializing it
    traceback.print_exc(file=sout)

# So I can't start a SyncManager ? But documentation says nothing about it
# I would expect I can do this as SyncManager is a subclass of BaseManager
sout.write(str(issubclass(sm.__class__, bm.__class__)) + '\n')

# So how to intialize the SyncManager ?
# print dir(sm) # Documentation says nothing about an init

# No methods above says anything about initializing a syncmanager.
# O.K then - maybe I need to pass a address to it like BaseManager ?

# That seems to work
sm2 = mmp.SyncManager(('', 12345))
print type(sm)

processes()
# Try starting it ?
sm2.start()

# Expected - now there are 3, parent Python, hidden sm and known sm2
processes()

# Shut sm2 down - good
sm2.shutdown()

# Not it is back to 2 - parent Python, hidden sm
processes()

# Can I shut sm down ?
sm.shutdown()

# Looks like that works
# But that is odd as I didn't start it!
processes()

# Maybe then I can do this ?
sm3 = mp.Manager(('', 12346))

# Looks like you cannot.