python多线程入门

January 12, 2023

进程

进程：https://docs.python.org/zh-cn/3/library/multiprocessing.html#process-and-exceptions

os 模块提供了操作系统相关的系统调用，multiprocessing 模块提供了跨平台的多进程

from multiprocessing import Process
import os

def info(title):
    print(title)
    print('module name:', __name__)
    print('parent process:', os.getppid())
    print('process id:', os.getpid())

def f(name):
    info('function f')
    print('hello', name)

if __name__ == '__main__':
    info('main line')
    p = Process(target=f, args=('bob',))
    p.start()
    p.join()

进程间通信，参见：https://docs.python.org/zh-cn/3/library/multiprocessing.html#exchanging-objects-between-processes

进程池：https://docs.python.org/zh-cn/3/library/multiprocessing.html#multiprocessing.pool.Pool

from multiprocessing import Pool
import os
import time
import random

def long_time_task(name):
    process_info = f'({name} pid={os.getpid():5})'
    print(f'[Start  Process] {process_info}')
    start = time.time()
    time.sleep(random.random() * 3)
    end = time.time()
    print(f'[End    Process] {process_info} takes {(end - start):.2f} seconds.')

if __name__ == '__main__':
    print(f'[Parent Process] (pid={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()  # 必须先关闭进程池
    print('All subprocesses done.')

子进程：https://docs.python.org/zh-cn/3/library/subprocess.html

import subprocess

subprocess.run(["ls", "-l"])

p = subprocess.run(["ls", "-l"], capture_output=True)
print(p.stdout.decode("utf-8"))

p = subprocess.run(["ls", "-l"], capture_output=True, encoding="utf-8")
print(p.stdout)


p = subprocess.Popen(["nslookup"], stdin=subprocess.PIPE,
                     stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                     )
output, err = p.communicate(
    br"""
set q=mx
python.org
exit
""")
print(output)
print('Exit code:', p.returncode)

线程

线程：https://docs.python.org/zh-cn/3/library/threading.html#threading.Thread

import threading
from threading import Thread

print(threading.current_thread().name)  # MainThread


def runnable(*args):
    print(threading.current_thread().name)
    print(args)


t1 = Thread(target=runnable, args=("hello", "world"))
t1.start()
t1.join()


# 若继承Thread对象，则可以覆写run方法（与java相似）
class MyThread(Thread):
    def run(self):
        print(threading.current_thread().name)


t2 = MyThread()
t2.start()
t2.join()

线程锁：https://docs.python.org/zh-cn/3/library/threading.html#lock-objects

import threading
from threading import Thread, Lock, RLock

lock = Lock()
rlock = RLock()  # 可重入锁
a = 0


def runnable1():
    global a
    lock.acquire()
    a += 1
    a -= 1
    lock.release()
    print(a)


def runnable2():
    # 保证锁可释放
    global a
    lock.acquire()
    try:
        a += 1
        a -= 1
    finally:
        lock.release()
    print(a)


def runnable3():
    # with 语法糖
    global a
    with lock:
        a += 1
        a -= 1
    print(a)


# 创建线程本地数据
mydata = threading.local()

def use_local_1():
    mydata.x = 1


def use_local_2():
    mydata.x = 2

标准库还提供了信号量和事件等机制：https://docs.python.org/zh-cn/3/library/threading.html

并行任务

https://docs.python.org/zh-cn/3/library/concurrent.futures.html

参见：https://python-parallel-programmning-cookbook.readthedocs.io/zh_CN/latest/

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