121 lines
4.7 KiB
Python
121 lines
4.7 KiB
Python
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import random
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import string
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import sys
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import threading
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import weakref
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class Local:
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"""
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A drop-in replacement for threading.locals that also works with asyncio
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Tasks (via the current_task asyncio method), and passes locals through
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sync_to_async and async_to_sync.
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Specifically:
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- Locals work per-coroutine on any thread not spawned using asgiref
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- Locals work per-thread on any thread not spawned using asgiref
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- Locals are shared with the parent coroutine when using sync_to_async
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- Locals are shared with the parent thread when using async_to_sync
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(and if that thread was launched using sync_to_async, with its parent
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coroutine as well, with this working for indefinite levels of nesting)
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Set thread_critical to True to not allow locals to pass from an async Task
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to a thread it spawns. This is needed for code that truly needs
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thread-safety, as opposed to things used for helpful context (e.g. sqlite
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does not like being called from a different thread to the one it is from).
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Thread-critical code will still be differentiated per-Task within a thread
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as it is expected it does not like concurrent access.
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This doesn't use contextvars as it needs to support 3.6. Once it can support
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3.7 only, we can then reimplement the storage more nicely.
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"""
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def __init__(self, thread_critical: bool = False) -> None:
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self._thread_critical = thread_critical
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self._thread_lock = threading.RLock()
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self._context_refs: "weakref.WeakSet[object]" = weakref.WeakSet()
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# Random suffixes stop accidental reuse between different Locals,
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# though we try to force deletion as well.
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self._attr_name = "_asgiref_local_impl_{}_{}".format(
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id(self),
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"".join(random.choice(string.ascii_letters) for i in range(8)),
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)
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def _get_context_id(self):
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"""
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Get the ID we should use for looking up variables
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"""
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# Prevent a circular reference
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from .sync import AsyncToSync, SyncToAsync
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# First, pull the current task if we can
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context_id = SyncToAsync.get_current_task()
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context_is_async = True
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# OK, let's try for a thread ID
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if context_id is None:
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context_id = threading.current_thread()
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context_is_async = False
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# If we're thread-critical, we stop here, as we can't share contexts.
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if self._thread_critical:
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return context_id
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# Now, take those and see if we can resolve them through the launch maps
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for i in range(sys.getrecursionlimit()):
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try:
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if context_is_async:
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# Tasks have a source thread in AsyncToSync
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context_id = AsyncToSync.launch_map[context_id]
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context_is_async = False
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else:
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# Threads have a source task in SyncToAsync
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context_id = SyncToAsync.launch_map[context_id]
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context_is_async = True
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except KeyError:
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break
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else:
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# Catch infinite loops (they happen if you are screwing around
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# with AsyncToSync implementations)
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raise RuntimeError("Infinite launch_map loops")
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return context_id
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def _get_storage(self):
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context_obj = self._get_context_id()
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if not hasattr(context_obj, self._attr_name):
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setattr(context_obj, self._attr_name, {})
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self._context_refs.add(context_obj)
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return getattr(context_obj, self._attr_name)
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def __del__(self):
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try:
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for context_obj in self._context_refs:
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try:
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delattr(context_obj, self._attr_name)
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except AttributeError:
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pass
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except TypeError:
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# WeakSet.__iter__ can crash when interpreter is shutting down due
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# to _IterationGuard being None.
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pass
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def __getattr__(self, key):
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with self._thread_lock:
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storage = self._get_storage()
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if key in storage:
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return storage[key]
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else:
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raise AttributeError(f"{self!r} object has no attribute {key!r}")
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def __setattr__(self, key, value):
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if key in ("_context_refs", "_thread_critical", "_thread_lock", "_attr_name"):
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return super().__setattr__(key, value)
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with self._thread_lock:
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storage = self._get_storage()
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storage[key] = value
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def __delattr__(self, key):
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with self._thread_lock:
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storage = self._get_storage()
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if key in storage:
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del storage[key]
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else:
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raise AttributeError(f"{self!r} object has no attribute {key!r}")
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