threading.local笔记

普通多线程修改同一数据

import threading
import time

v = 0

def task(n):
    global v
    v = n
    time.sleep(0.1)
    print(v)

l = []
for i in range(10):
    t = threading.Thread(target=task, args=(i,))
    l.append(t)
    t.start()

for p in l:
    p.join()


'''
结果为
9 
9
9
9
9
9 ...
'''

当多线程同时去修改同一个变量时，会出现数据不安全的情况，一般情况下会使用互斥锁来解决，代码如下：

import threading
import time

lock = threading.Lock()
v = 0

def task(n):
    global v
    lock.acquire()
    v = n
    time.sleep(0.1)
    lock.release()

    print(v)

l = []
for i in range(10):
    t = threading.Thread(target=task, args=(i,))
    l.append(t)
    t.start()

for p in l:
    p.join()
    
'''
结果为
0
1
2
3
4 ...
'''

threading.local对象

import threading
import time

obj = threading.local()


def task(n):
    obj.a = n
    time.sleep(0.1)

    print(obj.a)

l = []
for i in range(10):
    t = threading.Thread(target=task, args=(i,))
    l.append(t)
    t.start()

for p in l:
    p.join()

'''
结果为
5
2
6
1
0 ...
'''

threading.local作用：为每个线程创建一个独立的空间，使得线程对自己的空间中的数据进行操作（数据隔离）。

问题：

• 如何获取一个线程的唯一标记？ threading.get_ident()

• 根据字典自定义一个类似于threading.local功能？

  import threading
  import time
  
  DIC = {}
  
  def task(i):
      ident = threading.get_ident()
      if ident in DIC:
          DIC[ident]["stack"] = i
      else:
          DIC[ident] = {"stack": i}
  
      time.sleep(1)
  
      print(DIC[ident]["stack"])
  
  l = []
  for i in range(10):
      t = threading.Thread(target=task, args=(i,))
      l.append(t)
      t.start()
  
  for p in l:
      p.join()

• 根据字典自定义一个为每个协程开辟空间进行存取数据。

  import threading
  import greenlet
  import time
  
  DIC = {}
  
  def task(i):
      # ident = threading.get_ident()
      ident = greenlet.getcurrent()
      if ident in DIC:
          DIC[ident]["stack"] = i
      else:
          DIC[ident] = {"stack": i}
  
      time.sleep(1)
  
      print(DIC[ident]["stack"])
  
  l = []
  for i in range(10):
      t = threading.Thread(target=task, args=(i,))
      l.append(t)
      t.start()
  
  for p in l:
      p.join()

• 通过getattr/setattr 构造出来 threading.local的加强版（协程）

  import threading
  import time
  
  # 如果没有协程就使用线程ID
  try:
      import greenlet
      get_ident = greenlet.getcurrent
  except ImportError:
      get_ident = threading.get_ident
  
  class Local(object):
      DIC = {}
      
      # 获取
      def __getattr__(self, item):
          ident = get_ident()
          if ident in self.DIC:
              return self.DIC[ident].get(item)
          return None
      
      # 设置
      def __setattr__(self, key, value):
          ident = get_ident()
          if ident in self.DIC:
              self.DIC[ident][key] = value
          else:
              self.DIC[ident] = {key: value}
  
  obj = Local()
  
  def task(i):
      obj.stack = i
      time.sleep(1)
      print(obj.stack)
  
  l = []
  for i in range(10):
      t = threading.Thread(target=task, args=(i,))
      l.append(t)
      t.start()
  
  for p in l:
      p.join()