python 在threading中如何處理主進程和子線程的關系

更新時間：2020年04月25日 14:16:53 作者：chen_999876

這篇文章主要介紹了python 在threading中如何處理主進程和子線程的關系，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

之前用python的多線程，總是處理不好進程和線程之間的關系。后來發(fā)現了join和setDaemon函數，才終于弄明白。下面總結一下。

1.使用join函數后，主進程會在調用join的地方等待子線程結束，然后才接著往下執(zhí)行。

join使用實例如下：

import time
import random
import threading
 
class worker(threading.Thread):
  def __init__(self): 
    threading.Thread.__init__(self) 
  def run(self):
    t = random.randint(1,10)
    time.sleep(t)
    print "This is " + self.getName() + ";I sleep %d second."%(t)
    
tsk = []
for i in xrange(0,5):
  time.sleep(0.1)
  thread = worker()
  thread.start()
  tsk.append(thread)
for tt in tsk:
  tt.join()
print "This is the end of main thread."

運行結果如下：

# python testjoin.py 
This is Thread-3;I sleep 2 second.
This is Thread-1;I sleep 4 second.
This is Thread-2;I sleep 7 second.
This is Thread-4;I sleep 7 second.
This is Thread-5;I sleep 7 second.
This is the end of main thread.

這里創(chuàng)建了5個子線程，每個線程隨機等待1-10秒后打印退出；主線程分別等待5個子線程結束。最后結果是先顯示各個子線程，再顯示主進程的結果。

2. 如果使用的setDaemon函數，則與join相反，主進程結束的時候不會等待子線程。

setDaemon函數使用實例：

import time
import random
import threading
 
class worker(threading.Thread):
  def __init__(self): 
    threading.Thread.__init__(self) 
  def run(self):
    t = random.randint(1,10)
    time.sleep(t)
    print "This is " + self.getName() + ";I sleep %d second."%(t)
    
tsk = []
for i in xrange(0,5):
  time.sleep(0.1)
  thread = worker()
  thread.setDaemon(True)
  thread.start()
  tsk.append(thread)
print "This is the end of main thread."

這里設置主進程為守護進程，當主進程結束的時候，子線程被中止

運行結果如下：

#python testsetDaemon.py
This is the end of main thread.

3、如果沒有使用join和setDaemon函數，則主進程在創(chuàng)建子線程后，直接運行后面的代碼，主程序一直掛起，直到子線程結束才能結束。

import time
import random
import threading
 
class worker(threading.Thread):
  def __init__(self): 
    threading.Thread.__init__(self) 
  def run(self):
    t = random.randint(1,10)
    time.sleep(t)
    print "This is " + self.getName() + ";I sleep %d second."%(t)
    
tsk = []
for i in xrange(0,5):
  time.sleep(0.1)
  thread = worker()
  thread.start()
  tsk.append(thread)
print "This is the end of main thread."

運行結果如下：

# python testthread.py 
This is the end of main thread.
This is Thread-4;I sleep 1 second.
This is Thread-3;I sleep 7 second.
This is Thread-5;I sleep 7 second.
This is Thread-1;I sleep 10 second.
This is Thread-2;I sleep 10 second.

補充知識：Python Thread和Process對比

原因：進程和線程的差距（方向不同，之針對這個實例）

# coding=utf-8
import logging
import multiprocessing
import os
import time
from threading import Thread

logging.basicConfig(
  level=logging.INFO,
  format="%(asctime)s 【 %(process)d 】 %(processName)s %(message)s"
)


def func (i):
  # logging.info(f'子：{os.getpid()},\t{i}')
  return f'子：{os.getpid()},\t{i}'


def main (ctx):
  start01 = time.time()
  ts = [Thread(target=func, args=(i,)) for i in range(100)]
  [t.start() for t in ts]
  [t.join() for t in ts]
  end01 = time.time() - start01
  logging.info(f"線程花費的時間：{end01}秒")
  
  start02 = time.time()
  ps = [ctx.Process(target=func, args=(i,)) for i in range(100)]
  [p.start() for p in ps]
  [p.join() for p in ps]
  end02 = time.time() - start02
  logging.info(f"進程花費的時間：{end02}秒")


if __name__ == '__main__':
  # windows 啟動方式
  multiprocessing.set_start_method('spawn')
  # 獲取上下文
  ctx = multiprocessing.get_context('spawn')
  # 檢查這是否是凍結的可執(zhí)行文件中的偽分支進程。
  ctx.freeze_support()
  main(ctx)

輸出：