scalar = Value('i', 0) # shared memory: process/thread safe
vector = Array('d', procs) # type codes from ctypes: int, double

show start value in parent process

showdata('parent start', scalar, vector)

spawn child, pass in shared memory

p = Process(target=showdata, args=('child ', scalar, vector))
p.start(); p.join()

pass in shared memory updated in parent, wait for each to finish

each child sees updates in parent so far for args (but not global)

print('\nloop1 (updates in parent, serial children)...')
for i in range(procs):
count += 1
scalar.value += 1
vector[i] += 1
p = Process(target=showdata, args=(('process %s' % i), scalar, vector))
p.start(); p.join()

same as prior, but allow children to run in parallel

all see the last iteration's result because all share objects

print('\nloop2 (updates in parent, parallel children)...')
ps = []
for i in range(procs):
count += 1
scalar.value += 1
vector[i] += 1
p = Process(target=showdata, args=(('process %s' % i), scalar, vector))
p.start()
ps.append(p)
for p in ps: p.join()

shared memory updated in spawned children, wait for each

print('\nloop3 (updates in serial children)...')
for i in range(procs):
p = Process(target=updater, args=(scalar, vector))
p.start()
p.join()
showdata('parent temp', scalar, vector)

same, but allow children to update in parallel

ps = []
print('\nloop4 (updates in parallel children)...')
for i in range(procs):
p = Process(target=updater, args=(scalar, vector))
p.start()
ps.append(p)
for p in ps: p.join()

global count=6 in parent only

The multiprocessing Module| 251