python-基础：线程

3.线程安全

一个线程中可以有多个子线程，且线程可以共享进程中所有的资源

多个线程去操作一份资源，高概率性的发生数据混乱的情况，如下：

• 示例

import threading

loop = 100000000
number = 0


def _add(count):
    global number
    for i in range(count):
        number += 1


def _sub(count):
    global number
    for i in range(count):
        number -= 1


t1 = threading.Thread(target=_add, args=(loop,))
t2 = threading.Thread(target=_sub, args=(loop,))
t1.start()
t2.start()
t1.join()
t2.join()

print(number)

结果不符合预期

• 加入线程锁，解决“数据混乱”的问题

  import threading
  
  lock_object = threading.RLock()
  loop = 100000000
  number = 0
  
  
  def _add(count):
      lock_object.acquire()  # 加锁
      global number
      for i in range(count):
          number += 1
      lock_object.release()  # 释放锁
  
  
  def _sub(count):
      lock_object.acquire()  # 加锁
      global number
      for i in range(count):
          number -= 1
      lock_object.release()  # 释放锁
  
  
  t1 = threading.Thread(target=_add, args=(loop,))
  t2 = threading.Thread(target=_sub, args=(loop,))
  t1.start()
  # t1.join()主进程等待子进程
  # t1.setDaemo(Ture)主进程结束子进程
  t2.start()
  t1.join()
  t2.join()
  
  print(number)
  

  结果符合预期

• with 上下文管理锁

  import threading
  
  lock_object = threading.RLock()
  loop = 100000000
  number = 0
  
  
  def _add(count):
      with lock_object: ##上下文管理
          global number
          for i in range(count):
              number += 1
  
  
  
  def _sub(count):
      with lock_object: ##上下文管理
          global number
          for i in range(count):
              number -= 1
  
  
  
  t1 = threading.Thread(target=_add, args=(loop,))
  t2 = threading.Thread(target=_sub, args=(loop,))
  t1.start()
  # t1.join()主进程等待子进程
  # t1.setDaemo(Ture)主进程结束子进程
  t2.start()
  t1.join()
  t2.join()
  
  print(number)
  

• 线程安全的数据类型（内部集成了锁的机制）

  import threading
  
  lock_object = threading.RLock()
  data_list=[]
  
  def task():
      print('start')
      for i in range(100000000):
          data_list.append(i)
      print(len(data_list))
  
  for i in range(10):
      t=threading.Thread(target=task)
      t.start()
  

  以下操作为数据安全：

  L.append(x)

  L1.expend(L2)

  x=L(i)

  L1[i:j]=L2

  L.sort()

  x=y

  x.field=y

  D(x)=y

  D1.update(D2)

  D.keys()

  下面的不是数据安全

  i=i+1

  L.append（L[-1]）

  L[i]=L[j]

  D(x)=D(x)+1

多注意开文档中是否表明为数据安全