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import asyncio
import contextlib
import contextvars
import threading
from typing import Any, Dict, Union
class _CVar:
"""Storage utility for Local."""
def __init__(self) -> None:
self._data: "contextvars.ContextVar[Dict[str, Any]]" = contextvars.ContextVar(
"asgiref.local"
)
def __getattr__(self, key):
storage_object = self._data.get({})
try:
return storage_object[key]
except KeyError:
raise AttributeError(f"{self!r} object has no attribute {key!r}")
def __setattr__(self, key: str, value: Any) -> None:
if key == "_data":
return super().__setattr__(key, value)
storage_object = self._data.get({})
storage_object[key] = value
self._data.set(storage_object)
def __delattr__(self, key: str) -> None:
storage_object = self._data.get({})
if key in storage_object:
del storage_object[key]
self._data.set(storage_object)
else:
raise AttributeError(f"{self!r} object has no attribute {key!r}")
class Local:
"""Local storage for async tasks.
This is a namespace object (similar to `threading.local`) where data is
also local to the current async task (if there is one).
In async threads, local means in the same sense as the `contextvars`
module - i.e. a value set in an async frame will be visible:
- to other async code `await`-ed from this frame.
- to tasks spawned using `asyncio` utilities (`create_task`, `wait_for`,
`gather` and probably others).
- to code scheduled in a sync thread using `sync_to_async`
In "sync" threads (a thread with no async event loop running), the
data is thread-local, but additionally shared with async code executed
via the `async_to_sync` utility, which schedules async code in a new thread
and copies context across to that thread.
If `thread_critical` is True, then the local will only be visible per-thread,
behaving exactly like `threading.local` if the thread is sync, and as
`contextvars` if the thread is async. This allows genuinely thread-sensitive
code (such as DB handles) to be kept stricly to their initial thread and
disable the sharing across `sync_to_async` and `async_to_sync` wrapped calls.
Unlike plain `contextvars` objects, this utility is threadsafe.
"""
def __init__(self, thread_critical: bool = False) -> None:
self._thread_critical = thread_critical
self._thread_lock = threading.RLock()
self._storage: "Union[threading.local, _CVar]"
if thread_critical:
# Thread-local storage
self._storage = threading.local()
else:
# Contextvar storage
self._storage = _CVar()
@contextlib.contextmanager
def _lock_storage(self):
# Thread safe access to storage
if self._thread_critical:
try:
# this is a test for are we in a async or sync
# thread - will raise RuntimeError if there is
# no current loop
asyncio.get_running_loop()
except RuntimeError:
# We are in a sync thread, the storage is
# just the plain thread local (i.e, "global within
# this thread" - it doesn't matter where you are
# in a call stack you see the same storage)
yield self._storage
else:
# We are in an async thread - storage is still
# local to this thread, but additionally should
# behave like a context var (is only visible with
# the same async call stack)
# Ensure context exists in the current thread
if not hasattr(self._storage, "cvar"):
self._storage.cvar = _CVar()
# self._storage is a thread local, so the members
# can't be accessed in another thread (we don't
# need any locks)
yield self._storage.cvar
else:
# Lock for thread_critical=False as other threads
# can access the exact same storage object
with self._thread_lock:
yield self._storage
def __getattr__(self, key):
with self._lock_storage() as storage:
return getattr(storage, key)
def __setattr__(self, key, value):
if key in ("_local", "_storage", "_thread_critical", "_thread_lock"):
return super().__setattr__(key, value)
with self._lock_storage() as storage:
setattr(storage, key, value)
def __delattr__(self, key):
with self._lock_storage() as storage:
delattr(storage, key)
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