執行緒鎖的運用

多個執行緒對同乙個資料進行修改時， 可能會出現不可預料的情況.

# 1. 例項化乙個鎖物件;

#     lock = threading.lock()
# 2. 操作變數之前進行加鎖
#     lock.acquire()
# 3. 操作變數之後進行解鎖
#     lock.release()

import threading

#  以銀行存錢和取錢舉例
def add(lock):
global money  # 生命money為全域性變數
for i in range(1000):
# 2. 操作變數之前進行加鎖
lock.acquire()
money += 1
# 3. 操作變數之後進行解鎖
lock.release()
def reduce(lock):
global money
for i in range(1000):
# 2. 操作變數之前進行加鎖
lock.acquire()
money -= 1
# 3. 操作變數之後進行解鎖
lock.release()
if __name__ == '__main__':
money=0
# 1. 例項化乙個鎖物件;
lock = threading.lock()
t1 = threading.thread(target=add, args=(lock,))
t2 = threading.thread(target=reduce, args=(lock,))
t1.start()
t2.start()
t1.join()
t2.join()
print("當前金額:", money)
# 當使用繼承來實現多執行緒
import threading
class addthread(threading.thread):
def __init__(self, lock):
super(addthread, self).__init__()
self.lock = lock
def run(self):
for i in range(1000000):
# 2. 操作變數之前進行加鎖
self.lock.acquire()
global  money
money += 1  # money;  money+1; money=money+1;
# 3. 操作變數之後進行解鎖
self.lock.release()
class reducethread(threading.thread):
def __init__(self, lock):
super(reducethread, self).__init__()
self.lock = lock
def run(self):
global money
for i in range(1000000):
# 2. 操作變數之前進行加鎖
lock.acquire()
money -= 1
# 3. 操作變數之後進行解鎖
lock.release()
if __name__ == '__main__':
money = 0
# 1. 例項化乙個鎖物件;
lock = threading.lock()
t1 = addthread(lock)
t2 = reducethread(lock)
t1.start()
t2.start()
t1.join()
t2.join()
print("當前金額:", money)

from urllib.request import urlopen

download_dir = 'doc'

class downloadthread(threading.thread):

def __init__(self, url):

super(downloadthread, self).__init__()

self.url = url

def run(self):

try:

urlobj = urlopen(self.url)

except exception as e:

print("download %s error\n" % (self.url), e)

imgcontent = none

else:

filename = self.url.split("/")[-1]

# 'ab'

with open("%s/%s" % (download_dir, filename), 'ab') as f:

while true:

imgcontentchunk = urlobj.read(1024 * 3)

if not imgcontentchunk:

break

f.write(imgcontentchunk)

url1=''

url2=''

urls = [url1,url2]

for url in urls:

thread = downloadthread(url)

thread.start()

thread.join()

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