threading.local()源码分析

 1 class _localimpl:
 2     """A class managing thread-local dicts"""
 3     """管理线程局部字典的类"""
 4     __slots__ = ‘key‘, ‘dicts‘, ‘localargs‘, ‘locallock‘, ‘__weakref__‘
 5 
 6     def __init__(self):
 7         # The key used in the Thread objects‘ attribute dicts.
 8         # We keep it a string for speed but make it unlikely to clash with
 9         # a "real" attribute.
10         self.key = ‘_threading_local._localimpl.‘ + str(id(self))
11         # { id(Thread) -> (ref(Thread), thread-local dict) }
12         #字典变量中的值中以id(Thread)为key，当前线程的弱引用ref(Thread)和
13         #当前线程的局部变量字典（thread-local dict）组成的元组
14         self.dicts = {}
15 
16     def get_dict(self):
17         """Return the dict for the current thread. Raises KeyError if none
18         defined."""
19         """返回当前线程的局部变量字典，其是元组中的第二个元素"""
20         thread = current_thread()
21         return self.dicts[id(thread)][1]
22 
23     def create_dict(self):
24         """Create a new dict for the current thread, and return it."""
25         """为当前线程造建一个局部变量字典，用来保存局部变量"""
26         localdict = {}
27         key = self.key
28         thread = current_thread()
29         idt = id(thread)
30         def local_deleted(_, key=key):
31             # When the localimpl is deleted, remove the thread attribute.
32             # 定义一个弱引用的回调函数，当线程局部变量的管理类localimpl被删除时，从线程中删除对应的变量
33             thread = wrthread()
34             if thread is not None:
35                 del thread.__dict__[key]
36         def thread_deleted(_, idt=idt):
37             # When the thread is deleted, remove the local dict.
38             # Note that this is suboptimal if the thread object gets
39             # caught in a reference loop. We would like to be called
40             # as soon as the OS-level thread ends instead.
41             # 定义一个弱引用的回调函数，当线程被删除时，在管理类localimpl对象的字典中删除该线程的字典项
42             local = wrlocal()
43             if local is not None:
44                 dct = local.dicts.pop(idt)
45         #定义两个弱引用
46         wrlocal = ref(self, local_deleted)
47         wrthread = ref(thread, thread_deleted)
48         #线程和局部变量管理类相互关联
49         thread.__dict__[key] = wrlocal
50         #在字典中以线程id为key，保存了弱引用和线程局部变量的字典
51         self.dicts[idt] = wrthread, localdict
52         return localdict