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python主線程與子線程的結(jié)束順序?qū)嵗馕?/h1>

更新時(shí)間：2019年12月17日 09:11:45 作者：luozx207

這篇文章主要介紹了python主線程與子線程的結(jié)束順序?qū)嵗馕?文中通過示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友可以參考下

引用自主線程退出對(duì)子線程的影響的一段話：

對(duì)于程序來說，如果主進(jìn)程在子進(jìn)程還未結(jié)束時(shí)就已經(jīng)退出，那么Linux內(nèi)核會(huì)將子進(jìn)程的父進(jìn)程ID改為1（也就是init進(jìn)程），當(dāng)子進(jìn)程結(jié)束后會(huì)由init進(jìn)程來回收該子進(jìn)程。

主線程退出后子線程的狀態(tài)依賴于它所在的進(jìn)程，如果進(jìn)程沒有退出的話子線程依然正常運(yùn)轉(zhuǎn)。如果進(jìn)程退出了，那么它所有的線程都會(huì)退出，所以子線程也就退出了。

主線程退出，進(jìn)程等待所有子線程執(zhí)行完畢后才結(jié)束

進(jìn)程啟動(dòng)后會(huì)默認(rèn)產(chǎn)生一個(gè)主線程，默認(rèn)情況下主線程創(chuàng)建的子線程都不是守護(hù)線程（setDaemon(False)）。因此主線程結(jié)束后，子線程會(huì)繼續(xù)執(zhí)行，進(jìn)程會(huì)等待所有子線程執(zhí)行完畢后才結(jié)束

所有線程共享一個(gè)終端輸出（線程所屬進(jìn)程的終端）

import threading
import time
def child_thread1():
  for i in range(100):
    time.sleep(1)
    print('child_thread1_running...')
def parent_thread():
  print('parent_thread_running...')
  thread1 = threading.Thread(target=child_thread1)
  thread1.start()
  print('parent_thread_exit...')
if __name__ == "__main__":
  parent_thread()

輸出為：

parent_thread_running...
parent_thread_exit...
child_thread1_running...
child_thread1_running...
child_thread1_running...
child_thread1_running...
...

可見父線程結(jié)束后，子線程仍在運(yùn)行，此時(shí)結(jié)束進(jìn)程，子線程才會(huì)被終止

主線程結(jié)束后進(jìn)程不等待守護(hù)線程完成，立即結(jié)束

當(dāng)設(shè)置一個(gè)線程為守護(hù)線程時(shí)，此線程所屬進(jìn)程不會(huì)等待此線程運(yùn)行結(jié)束，進(jìn)程將立即結(jié)束

import threading
import time
def child_thread1():
  for i in range(100):
    time.sleep(1)
    print('child_thread1_running...')
def child_thread2():
  for i in range(5):
    time.sleep(1)
    print('child_thread2_running...')
def parent_thread():
  print('parent_thread_running...')
  thread1 = threading.Thread(target=child_thread1)
  thread2 = threading.Thread(target=child_thread2)
  thread1.setDaemon(True)
  thread1.start()
  thread2.start()
  print('parent_thread_exit...')
if __name__ == "__main__":
  parent_thread()

輸出：

parent_thread_running...
parent_thread_exit...
child_thread1_running...child_thread2_running...

child_thread1_running...child_thread2_running...

child_thread1_running...child_thread2_running...

child_thread1_running...child_thread2_running...

child_thread2_running...child_thread1_running...

Process finished with exit code 0

thread1是守護(hù)線程，thread2非守護(hù)線程，因此，進(jìn)程會(huì)等待thread2完成后結(jié)束，而不會(huì)等待thread1完成

注意：子線程會(huì)繼承父線程中daemon的值，即守護(hù)線程開啟的子線程仍是守護(hù)線程

主線程等待子線程完成后結(jié)束

在線程A中使用B.join()表示線程A在調(diào)用join()處被阻塞，且要等待線程B的完成才能繼續(xù)執(zhí)行

import threading
import time

def child_thread1():
  for i in range(10):
    time.sleep(1)
    print('child_thread1_running...')

def child_thread2():
  for i in range(5):
    time.sleep(1)
    print('child_thread2_running...')

def parent_thread():
  print('parent_thread_running...')
  thread1 = threading.Thread(target=child_thread1)
  thread2 = threading.Thread(target=child_thread2)
  thread1.setDaemon(True)
  thread2.setDaemon(True)
  thread1.start()
  thread2.start()
  thread2.join()
  1/0
  thread1.join()
  print('parent_thread_exit...')

if __name__ == "__main__":
  parent_thread()

輸出：

parent_thread_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
child_thread1_running...
child_thread2_running...
Traceback (most recent call last):
 File "E:/test_thread.py", line 31, in <module>
  parent_thread()
 File "E:/test_thread.py", line 25, in parent_thread
  1/0
ZeroDivisionError: integer division or modulo by zero

主線程在執(zhí)行到thread2.join()時(shí)被阻塞，等待thread2結(jié)束后才會(huì)執(zhí)行下一句

1/0 會(huì)使主線程報(bào)錯(cuò)退出，且thread1設(shè)置了daemon=True，因此主線程意外退出時(shí)thread1也會(huì)立即結(jié)束。thread1.join()沒有被主線程執(zhí)行

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