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
  """