Class _localimpl

Lib/_threading_local.py:24–65

A class managing thread-local dicts

# manifest.

class _localimpl:
    """A class managing thread-local dicts"""
    __slots__ = 'key', 'dicts', 'localargs', 'locallock', '__weakref__'

    def __init__(self):
        # The key used in the Thread objects' attribute dicts.
        # We keep it a string for speed but make it unlikely to clash with
        # a "real" attribute.
        self.key = '_threading_local._localimpl.' + str(id(self))
        # { id(Thread) -> (ref(Thread), thread-local dict) }
        self.dicts = {}

    def get_dict(self):
        """Return the dict for the current thread. Raises KeyError if none
        defined."""
        thread = current_thread()
        return self.dicts[id(thread)][1]

    def create_dict(self):
        """Create a new dict for the current thread, and return it."""
        localdict = {}
        key = self.key
        thread = current_thread()
        idt = id(thread)
        def local_deleted(_, key=key):
            # When the localimpl is deleted, remove the thread attribute.
            thread = wrthread()
            if thread is not None:
                del thread.__dict__[key]
        def thread_deleted(_, idt=idt):
            # When the thread is deleted, remove the local dict.
            # Note that this is suboptimal if the thread object gets
            # caught in a reference loop. We would like to be called
            # as soon as the OS-level thread ends instead.
            local = wrlocal()
            if local is not None:
                local.dicts.pop(idt)
        wrlocal = ref(self, local_deleted)
        wrthread = ref(thread, thread_deleted)
        thread.__dict__[key] = wrlocal
        self.dicts[idt] = wrthread, localdict
        return localdict


@contextmanager