multiprocessing
conceptual
Basic Flow of Creating Multiple Processes
Creating process objects
Starting processes Recycling processes
Code:
import multiprocessing as mp
from time import sleep
# Process execution functions
def fun():
print("Start a process")
sleep(3)
print("End of process")
# Create process objects
p = (target = fun)
() # Start the process
() # Recovery process
Run results:
Starting a process
process termination
Process finished with exit code 0
1, the parent and child processes are executed in parallel child process execution function parent process execution in addition to the contents of the child process:
import multiprocessing as mp
from time import sleep
# Process execution functions
def fun():
print("Start a process")
sleep(3)
print("End of process")
# Create process objects
p = (target = fun) # Make the fun function a separate child process Other functions are executed by the process.
() # Start the process
sleep(2)
print("What the parent process executes")
() # Recovery process
print("===============")
"""
pid =
if pid == 0
fun()
os._exit(0)
else:
()
"""
Run results:
Starting a process
What the parent process executes
process termination
===============
2, the child process can not change the value of variables in the parent process
Code:
import multiprocessing as mp
from time import sleep
a = 1
# Process execution functions
def fun():
print("Start a process")
sleep(3)
global a
print("a=", a)
a = 1000
print("a=", a)
print("End of process")
# Create process objects
p = (target = fun) # Make the fun function a separate child process Other functions are executed by the process.
() # Start the process
sleep(2)
print("What the parent process executes")
() # Recovery process
print("===============")
print("a=", a)
Run results:
Starting a process
What the parent process executes
a= 1
a= 1000
process termination
a= 1
Creating multiple processes
Code:
"""
Creating multiple processes
"""
from multiprocessing import Process
import os
from time import sleep
def fun1():
sleep(2)
print((), '--', (), "Eat.")
def fun2():
sleep(3)
print((), '--', (), "Sleep.")
def fun3():
sleep(4)
print((), '--', (), "Learning.")
jobs =[]
for th in [fun1, fun2, fun3]:
p = Process(target = th)
(p)
()
for i in jobs:
()
Run results:
46013 - 46022 Eating
46013 - 46023 Sleeping
46013 - 46024 Study
Process functions with parameters
Code:
from multiprocessing import Process
from time import sleep
# Process functions with parameters
def worker(sec, name):
for i in range(3):
sleep(sec)
print("I'm %s"%name)
print("I'm working...")
# p = Process(target = worker, args = (2, "Tom"))
p = Process(target = worker, kwargs = {'name':'tom', 'sec': 2})
()
()
Run results:
I'm tom
I'm working…
I'm tom
I'm working…
I'm tom
I'm working…
Case Exercise
Code:
from multiprocessing import Process
import os
filename = './'
size = (filename)
# Copy the top half
def up():
fr = open(filename, 'rb')
fw = open('bot,jpg', 'wb')
n = size//2
((n))
()
()
# Copy the second half
def down():
fr = open(filename, 'rb')
fw = open('bot,jpg', 'wb')
(size//2.0)
(())
()
()
p = Process(target = up)
q = Process(target = down)
()
()
()
()
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