Killing zombies

zombies.py

import os
import time
from subprocess import Popen


def check_zombies(expected_nzombies):
    # NOTE: don't use Popen() here
    output = os.popen(r"ps aux | grep ' Z' | grep -v grep").read()
    got_nzombies = len(output.splitlines())
    if got_nzombies > 0:
        print 'You have zombies!'
        print(output)
    else:
        print 'You are zombie-free!'
    assert expected_nzombies == got_nzombies, '%d != %d' % (
        expected_nzombies, got_nzombies)


# Start with no zombies
check_zombies(0)

# Make zombies
n = 3
for _ in xrange(n):
    Popen("sleep 1", shell=True)

# No zombies so far
check_zombies(0)

# Wait for children to terminate and become zombies
print 'Sleep'
time.sleep(2)

# Zombies?
check_zombies(n)

# Yes!
raw_input('Paused')

zombies_gc.py

import os
import time
from subprocess import Popen
import gc


def check_zombies(expected_nzombies):
    # NOTE: don't use Popen() here
    output = os.popen(r"ps aux | grep ' Z' | grep -v grep").read()
    got_nzombies = len(output.splitlines())
    if got_nzombies > 0:
        print 'You have zombies!'
        print(output)
    else:
        print 'You are zombie-free!'
    assert expected_nzombies == got_nzombies, '%d != %d' % (
        expected_nzombies, got_nzombies)


# Start with no zombies
check_zombies(0)

# Make zombies
n = 3
for _ in xrange(n):
    Popen("sleep 1", shell=True)

# No zombies so far
check_zombies(0)

# Wait for children to terminate and become zombies
print 'Sleep'
time.sleep(2)

# Zombies?
check_zombies(n)

# Try GC
print 'GC'
gc.collect()

# Zombies?
check_zombies(n)

# Yes!
raw_input('Paused')

zombies_gc_refs.py

import os
import time
from subprocess import Popen
import gc


def check_zombies(expected_nzombies):
    # NOTE: don't use Popen() here
    output = os.popen(r"ps aux | grep ' Z' | grep -v grep").read()
    got_nzombies = len(output.splitlines())
    if got_nzombies > 0:
        print 'You have zombies!'
        print(output)
    else:
        print 'You are zombie-free!'
    assert expected_nzombies == got_nzombies, '%d != %d' % (
        expected_nzombies, got_nzombies)


# Start with no zombies
check_zombies(0)

# Make zombies
n = 3
procs = []
for _ in xrange(n):
    procs.append(Popen("sleep 1", shell=True))

# No zombies so far
check_zombies(0)

# Wait for children to terminate and become zombies
print 'Sleep'
time.sleep(2)

# Zombies?
check_zombies(n)

# Explicitely del proc references
print 'Del procs references'
del procs

# Zombies?
check_zombies(0)

# No!
raw_input('Paused')

zombies_sweep.py

import os
import time
from subprocess import Popen


def check_zombies(expected_nzombies):
    # NOTE: don't use Popen() here
    output = os.popen(r"ps aux | grep ' Z' | grep -v grep").read()
    got_nzombies = len(output.splitlines())
    if got_nzombies > 0:
        print 'You have zombies!'
        print(output)
    else:
        print 'You are zombie-free!'
    assert expected_nzombies == got_nzombies, '%d != %d' % (
        expected_nzombies, got_nzombies)


# Start with no zombies
check_zombies(0)

# Make zombies
n = 3
for _ in xrange(n):
    Popen("sleep 1", shell=True)

# No zombies so far
check_zombies(0)

# Wait for children to terminate and become zombies
print 'Sleep'
time.sleep(2)

# Zombies?
check_zombies(n)

# Sweep process table and remove zombies
for _ in xrange(n):
    try:
        print os.waitpid(-1, os.WNOHANG)
    except Exception as exc:
        print exc
        break

# Zombies?
check_zombies(0)

# No!
raw_input('Paused')