Python 进程与线程小随笔

Process
涉及模块：multiprocessing

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• Process

  • p = Process()
  • p.start()
  • p.join()

from multiprocessing import Process
import os

# 子进程要执行的代码
def run_proc(name):
    print('Run child process %s (%s)...' % (name, os.getpid()))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Process(target=run_proc, args=('test',))
    print('Child process will start.')
    p.start()
    p.join()
    print('Child process end.')

• Pool

  • p=Pool(5)
  • p.apply_async(func,**args)
  • p.close()
  • p.join()

from multiprocessing import Pool
import os, time, random

def long_time_task(name):
    print('Run task %s (%s)...' % (name, os.getpid()))
    start = time.time()
    time.sleep(random.random() * 3)
    end = time.time()
    print('Task %s runs %0.2f seconds.' % (name, (end - start)))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Pool(4)
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print('Waiting for all subprocesses done...')
    p.close()
    p.join()
    print('All subprocesses done.')

Thread
涉及模块：threading

• Thread
  • t = threading.Thread(target=xxx,name=xxx,args=(xxx,xxx))
  • t.start()
  • t.join()
  • threading.curent_thread().name
  • l = threading.Lock()
  • l.acquire()
  • l.release()

import time, threading

# 新线程执行的代码:
def loop(s):
    print(s)
    print('thread %s is running...' % threading.current_thread().name)
    n = 0
    while n < 5:
        n = n + 1
        print('thread %s >>> %s' % (threading.current_thread().name, n))
        time.sleep(1)
    print('thread %s ended.' % threading.current_thread().name)

print('thread %s is running...' % threading.current_thread().name)
t = threading.Thread(target=loop, name='LoopThread', args=('a',))
t.start()
t.join()
print('thread %s ended.' % threading.current_thread().name)

• ThreadLocal
  • 线程中共享所有的全局变量，需注意是否会死锁
  • 局部只有当前线程可以进行操作，但调用会很麻烦
  • local = threading.local()

import threading

# 创建全局ThreadLocal对象:
local_school = threading.local()

def process_student():
    # 获取当前线程关联的student:
    std = local_school.student
    print('Hello, %s (in %s)' % (std, threading.current_thread().name))

def process_thread(name):
    # 绑定ThreadLocal的student:
    local_school.student = name
    process_student()

t1 = threading.Thread(target= process_thread, args=('Alice',), name='Thread-A')
t2 = threading.Thread(target= process_thread, args=('Bob',), name='Thread-B')
t1.start()
t2.start()
t1.join()
t2.join()

第三方进程与线程模块
涉及模块：concurrent.futures

• ThreadPoolExecutor、ProcessPoolExecutor

  • submit
  • map
  • concurrent.futures.as_completed

• zip

  • 拼接
  • zip((1,2),(10,20)) ->((1,10),(2,20))

def sim_add(a):
    return a[0]+a[1]
    
from concurrent.futures import ThreadPoolExecutor
import concurrent.futures

with ThreadPoolExecutor(max_workers=1) as t1:
    future1 = t1.submit(sim_add,(1,2))
    print(future1.result())

print()
var = [(1,2),(10,20),(100,200)]
with ThreadPoolExecutor(max_workers=2) as t:
    future = {t.submit(sim_add,tem): tem for tem in var}
    for parameter,res in zip(var,concurrent.futures.as_completed(future)):
        print("sim_add %s,return %s" % (parameter,res))
    # 多次submit，不接收结果但是又想全部执行完
    # concurrent.futures.wait()
print()
with ThreadPoolExecutor(max_workers=2) as t:
    for f in t.map(sim_add,[(1,2),(2,3)]):
        print(f)