Python3的进程和线程你了解吗
来源:脚本之家    时间:2022-03-15 12:22:13
目录
1.概述2.多进程3.子进程4.进程间通信5.多线程6.Lock7.ThreadLocal8.进程VS线程9.分布式进程总结

1.概述

"""
基础知识:
1.多任务:操作系统可以同时运行多个任务;
2.单核CPU执行多任务:操作系统轮流让各个任务交替执行;
3.一个任务即一个进程(process),如:打开一个浏览器,即启动一个浏览器进程;
4.在一个进程内,要同时干多件事,需要同时运行多个子任务,把进程内的子任务称为"线程(Thread)";
5.每个进程至少做一件事,因此,一个进程至少有一个线程;
同时执行多线程的解决方案:
a.启动多个进程,每个进程虽然只有一个线程,但多个进程可以一块执行多个任务;
b.启动一个进程,在一个进程内启动多个线程,多个线程一块执行多个任务;
c.启动多个进程,每个进程启动多个线程;
即多任务的实现方式:
a.多进程模式;
b.多线程模式;
c.多进程+多线程模式;
"""

2.多进程

import os
print("Process (%s) start..." % os.getpid())
"""
只能在Linux/Unix/Mac上工作
pid = os.fork()
if pid == 0:
    print("I am child process (%s) and my parent is %s." % (os.getpid(), os.getppid()))
else:
    print("I (%s) just created a child process (%s)." % (os.getpid(), pid))
"""
print("Hello.")
# multiprocessing:跨平台多线程模块
# process_test.py文件,在交互下python process_test.py
from multiprocessing import Process
import os
def run_process(name):
    print("Run child process %s (%s)..." % (name, os.getpid()))
if __name__ == "__main__":
    print("Parent process %s." % os.getpid())
    p = Process(target = run_process, args = ("test",))
    print("Child process will start.")
    p.start()
    p.join()        # join()方法可以等待子进程结束后再继续往下运行,用于进程间的同步
    print("Child process end.")

# 结果输出:
Parent process 28340.
Child process will start.
Run child process test (31152)...
Child process end.

# Pool:用进程池批量创建子进程
# process.py文件,交互下python process.py
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.")

# 结果输出:
Parent process 31576.
Waiting for all subprocesses done...
Run task 0 (20416)...
Run task 1 (15900)...
Run task 2 (24716)...
Run task 3 (31148)...
Task 2 runs 0.72 seconds.
Run task 4 (24716)...
Task 4 runs 1.03 seconds.
Task 3 runs 1.82 seconds.
Task 1 runs 2.73 seconds.
Task 0 runs 2.82 seconds.
All subprocesses done.

3.子进程

# subprocess模块:启动一个子进程,控制其输入和输出
# subprocess_test.py文件,注:文件名不要和模块名相同,否则报错
import subprocess
print("$ nslookup www.python.org")
r = subprocess.call(["nslookup", "www.python.org"])
print("Exit code:", r)

# 结果输出:
$ nslookup www.python.org
服务器: cache-a.guangzhou.gd.cn
Address: 202.96.128.86
非权威应答:
名称: www.python.org
Addresses: 2a04:4e42:1a::223
151.101.72.223
Exit code: 0

# 子进程需要输入,通过communicate()方法
import subprocess
print("$ nslookup")
p = subprocess.Popen(["nslookup"], stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
output, err = p.communicate(b"set q = mx\npython.org\nexit\n")
print(output.decode("gbk"))
print("Exit code:", p.returncode)

# 结果输出:
$ nslookup
默认服务器: cache-a.guangzhou.gd.cn
Address: 202.96.128.86
> Unrecognized command: set q = mx
> 服务器: cache-a.guangzhou.gd.cn
Address: 202.96.128.86
名称: python.org
Address: 138.197.63.241
>
Exit code: 0

4.进程间通信

# 在父进程中创建两个子进程,一个往Queue里写数据,一个从Queue里读数据
# queue_test.py文件,交互下python queue_test.py
from multiprocessing import Process, Queue
import os, time, random
def write(q):
    print("Process to write:%s" % os.getpid())
    for value in ["W", "I", "L", "L", "A", "R", "D"]:
        print("Put %s to queue..." % value)
        q.put(value)
        time.sleep(random.random())
def read(q):
    print("Process to read:%s" % os.getpid())
    while True:
        value = q.get(True)
        print("Get %s from queue." % value)
if __name__ == "__main__":
    # 父进程创建Queue,并传给各个子进程
    q = Queue()
    pw = Process(target = write, args = (q,))
    pr = Process(target = read, args = (q,))
    # 启动子进程pw,写入
    pw.start()
    # 启动子进程pr,读取
    pr.start()
    # 等待pw结束
    pw.join()
    # pr进程是死循环,无法等待其结束,需要强行终止
    pr.terminate()

# 结果输出:
Process to write:15720
Process to read:21524
Put W to queue...
Get W from queue.
Put I to queue...
Get I from queue.
Put L to queue...
Get L from queue.
Put L to queue...
Get L from queue.
Put A to queue...
Get A from queue.
Put R to queue...
Get R from queue.
Put D to queue...
Get D from queue.

5.多线程

# 线程库:_thread和threading
# 启动一个线程:即把一个函数传入并创建一个Thread实例,然后调用start()开始执行
# 任何进程默认启动一个线程,该线程称为主线程,主线程可以启动新的线程
# current_thread()函数:返回当前线程的实例;
# 主线程实例名字:MainThread;
# 子线程名字的创建时指定,如果不指定,则自动给线程命名为Thread-1、Thread-2...
import time, threading
def loop():
    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)
thread1 = threading.Thread(target = loop, name = "LoopThread")
thread1.start()
thread1.join()
print("Thread %s ended." % threading.current_thread().name)

# 结果输出:
Thread MainThread is running...
Thread LoopThread is running...
Thread LoopThread >>> 1
Thread LoopThread >>> 2
Thread LoopThread >>> 3
Thread LoopThread >>> 4
Thread LoopThread >>> 5
Thread LoopThread ended.
Thread MainThread ended.

6.Lock

# 多进程:同一个变量,各自有一份拷贝存在于每个进程中,互不影响;
# 多线程:所有变量由所有线程共享,任何一个变量可以被任何一个线程修改;
# 多线程同时操作一个变量
# 多运行几次,发现结果不为0
import time, threading
balance = 0
def change_it(n):
    global balance
    balance = balance + n
    balance = balance - n
def run_thread(n):
    # 线程交替执行,balance结果不一定为0
    for i in range(2000000):
        change_it(n)
thread1 = threading.Thread(target = run_thread, args = (5,))
thread2 = threading.Thread(target = run_thread, args = (8,))
thread1.start()
thread2.start()
thread1.join()
thread2.join()
print(balance)
# 结果输出:
# 5(各自不同)
# 确保balance计算正确,需要给change_it()上一把锁
# 当线程开始执行change_it()时,该线程获得锁,其他线程不能同时执行change_it(),
# 只能等待,直到锁被释放,获得该锁后才能改;
# 通过threading.Lock()创建锁
import time, threading
balance = 0
lock = threading.Lock()
def change_it(n):
    global balance
    balance = balance + n
    balance = balance - n
def run_thread(n):
    for i in range(2000000):
        lock.acquire()
        try:
            change_it(n)
        finally:
            # 释放锁
            lock.release()
thread1 = threading.Thread(target = run_thread, args = (5,))
thread2 = threading.Thread(target = run_thread, args = (8,))
thread1.start()
thread2.start()
thread1.join()
thread2.join()
print(balance)
# 结果输出:
# 0

7.ThreadLocal

# 多线程环境下,每个线程有自己的数据;
# 一个线程使用自己的局部变量比使用全局变量好;
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()
thread1 = threading.Thread(target = process_thread, args = ("Willard",), name = "Thread-1")
thread2 = threading.Thread(target = process_thread, args = ("WenYu",), name = "Thread-2")
thread1.start()
thread2.start()
thread1.join()
thread2.join()

# 结果输出:
# Hello,Willard (in Thread-1)
# Hello,WenYu (in Thread-2)

8.进程VS线程

# 进程和线程优缺点:
# 1.要实现多任务,会设计Master-Worker模式,Master负责分配任务,Worker负责执行任务,
# 在多任务环境下,通常是一个Master,多个Worker;
#     a.如果使用多进程实现Master-Worker,主进程即Master,其他进程即Worker;
#     b.如果使用多线程实现Master-Worker,主线程即Master,其他线程即Worker;
# 2.多进程优点:稳定性高,一个子进程崩溃不会影响主进程和其他子进程;
# 3.多进程缺点:创建进程的代价大,操作系统能同时运行的进程数有限;
# 4.多线程缺点:任何一个线程崩溃,可能直接造成整个进程崩溃;
# 线程切换:
# 1.依次完成任务的方式称为单任务模型,或批处理任务模型;
# 2.任务1先做n分钟,切换到任务2做n分钟,再切换到任务3做n分钟,依此类推,称为多任务模型;
# 计算密集型 VS IO密集型
# 1.计算密集型任务:要进行大量的计算,消耗CPU资源,如:对视频进行高清解码等;
# 2.IO密集型任务:涉及到网络、磁盘IO的任务,均为IO密集型任务;
# 3.IO密集型任务消耗CPU少,大部分时间在等待IO操作完成;
# 异步IO
# 1.事件驱动模型:用单进程单线程模型来执行多任务;
# 2.Python语言中,单线程的异步编程模型称为协程;

9.分布式进程

"""
实例:
有一个通过Queue通信的多进程程序在同一机器上运行,但现在处理任务的进程任务繁重,
希望把发送任务的进程和处理任务的进程发布到两台机器上;
"""
# task_master_test.py
# 交互环境中:python task_master_test.py
import random, time, queue
from multiprocessing.managers import BaseManager
# 发送任务的队列
task_queue = queue.Queue()
# 接收结果的队列
result_queue = queue.Queue()
def return_task_queue():
    global task_queue
    return task_queue
def return_result_queue():
    global task_queue
    return task_queue
# 从BaseManager继承的QueueManager
class QueueManager(BaseManager):
    pass
if __name__ == "__main__":
    # 把两个Queue注册到网络上,callable参数关联Queue对象
    QueueManager.register("get_task_queue", callable = return_task_queue)
    QueueManager.register("get_result_queue", callable = return_result_queue)
    # 绑定端口5000,设置验证码"Willard"
    manager = QueueManager(address = ("127.0.0.1", 5000), authkey = b"Willard")
    # 启动Queue
    manager.start()
    # 获得通过网络访问的Queue对象
    task = manager.get_task_queue()
    result = manager.get_result_queue()
    # 放任务进去
    for i in range(10):
        n = random.randint(0, 10000)
        print("Put task %d..." % n)
        task.put(n)
    # 从result队列读取结果
    print("Try get results...")
    for i in range(10):
        r = result.get(timeout = 10)
        print("Result:%s" % r)
    # 关闭
    manager.shutdown()
    print("Master Exit.")
# task_worker_test.py文件
# 交互环境python task_worker_test.py
import time, sys, queue
from multiprocessing.managers import BaseManager
# 创建QueueManager
class QueueManager(BaseManager):
    pass
QueueManager.register("get_task_queue")
QueueManager.register("get_result_queue")
# 连接到服务器
server_address = "127.0.0.1"
print("Connect to server %s..." % server_address)
# 端口和验证码
m = QueueManager(address = (server_address, 5000), authkey = b"Willard")
# 网络连接
m.connect()
# 获取Queue对象
task = m.get_task_queue()
result = m.get_result_queue()
# 从task队列取任务,把结果写入result队列
for i in range(10):
    try:
        n = task.get(timeout = 1)
        print("Run task %d * %d..." % (n, n))
        r = "%d * %d = %d" % (n, n, n * n)
        time.sleep(1)
        result.put(r)
    except Queue.Empty:
        print("Task queue is empty.")
print("Worker Exit.")

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