python多线程

python多线程

python多线程简介

python多线程时间并非是并行得,而是并发的,是多线程交替执行达到得并发效果

单线程实现食堂打饭操作

需求: 一个人打四份饭耗时

import time
"""
io密集型
"""
foods = 0
import threading

def get_food():
"""
食堂大妈打饭
"""
global foods
time.sleep(1)
foods += 1
print("大妈打了一份饭")

def take_food(name="1"):
"""
学生去打饭
"""
while foods < 4 :
time.sleep(1)
get_food()
time.sleep(1)
print(name + "打饭完成")

t1 = time.time()
take_food()
t2 = time.time()
print("一个人打完4份饭的时间==", t2-t1)

输出结果:
大妈打了一份饭
1打饭完成
大妈打了一份饭
1打饭完成
大妈打了一份饭
1打饭完成
大妈打了一份饭
1打饭完成
一个人打完4份饭的时间== 12.092403650283813

多线程实现食堂打饭

import time

"""
io密集型
"""
import threading

foods = 0
lock = threading.Lock()

def get_food():
"""
食堂大妈打饭
"""
global foods
time.sleep(1)
foods += 1
print("大妈打了一份饭")

def take_food(name="1"):
"""
学生去打饭
"""

global foods, lock
lock.acquire()
time.sleep(1)
get_food()
time.sleep(1)
print(name + "打饭完成")
print("foods值为", foods)
lock.release()

多线程

t1 = time.time()
for i in range(3):
th = threading.Thread(target=take_food, args=(str(i),))
th.start()
t2 = time.time()
print("3个人打完4份饭的时间==", t2 - t1)

输出结果:
3个人打完4份饭的时间== 0.0010788440704345703
大妈打了一份饭
0打饭完成
foods值为 1
大妈打了一份饭
1打饭完成
foods值为 2
大妈打了一份饭
2打饭完成
foods值为 3

多线程实现取钱

• 未加锁
  import threading
  import time

  banlence = 800

  def with_draw(money,name):
  global banlence
  if money <= banlence:
  banlence -= money
  print(name + "取钱成功")
  print("可用余额:", banlence)
  else:
  print(name + "取钱失败")

  th1 = threading.Thread(target=with_draw, args=(500, "张三"))
  th2 = threading.Thread(target=with_draw, args=(500, "李四"))
  th1.start()
  th2.start()
  """
  输出结果:
  张三取钱成功
  可用余额: -200
  李四取钱失败
  """

• 加锁
  # 多线程去取钱时数据不安全,需要加锁

  banlence = 800
  lock = threading.Lock()

  def with_draw(money, name):
  global banlence, lock
  # 加锁
  lock.acquire()
  if money <= banlence:
  time.sleep(0.1)
  banlence = banlence - money
  print(name + "取钱成功")
  print(threading.current_thread().name)

  print("可用余额:", banlence)
  else:
  print(name + "取钱失败")
  # 释放安全锁. 线程2要使用这个方法时需要等线程1使用完
  lock.release()

  th1 = threading.Thread(target=with_draw, args=(500, "张三"))
  th2 = threading.Thread(target=with_draw, args=(500, "李四"))
  th1.start()
  th2.start()
  """
  张三取钱成功
  Thread-1
  可用余额: 300
  李四取钱失败
  """