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66 lines
2.1 KiB
Python
66 lines
2.1 KiB
Python
from contextvars import ContextVar
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from typing import Generic, TypeVar
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T = TypeVar("T")
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class HiddenValue:
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pass
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_default = HiddenValue()
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class RecyclableContextVar(Generic[T]):
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"""
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RecyclableContextVar is a wrapper around ContextVar
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It's safe to use in gunicorn with thread recycling, but features like `reset` are not available for now
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NOTE: you need to call `increment_thread_recycles` before requests
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"""
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_thread_recycles: ContextVar[int] = ContextVar("thread_recycles")
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@classmethod
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def increment_thread_recycles(cls):
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try:
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recycles = cls._thread_recycles.get()
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cls._thread_recycles.set(recycles + 1)
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except LookupError:
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cls._thread_recycles.set(0)
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def __init__(self, context_var: ContextVar[T]):
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self._context_var = context_var
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self._updates = ContextVar[int](context_var.name + "_updates", default=0)
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def get(self, default: T | HiddenValue = _default) -> T:
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thread_recycles = self._thread_recycles.get(0)
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self_updates = self._updates.get()
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if thread_recycles > self_updates:
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self._updates.set(thread_recycles)
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# check if thread is recycled and should be updated
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if thread_recycles < self_updates:
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return self._context_var.get()
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else:
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# thread_recycles >= self_updates, means current context is invalid
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if isinstance(default, HiddenValue) or default is _default:
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raise LookupError
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else:
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return default
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def set(self, value: T):
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# it leads to a situation that self.updates is less than cls.thread_recycles if `set` was never called before
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# increase it manually
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thread_recycles = self._thread_recycles.get(0)
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self_updates = self._updates.get()
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if thread_recycles > self_updates:
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self._updates.set(thread_recycles)
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if self._updates.get() == self._thread_recycles.get(0):
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# after increment,
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self._updates.set(self._updates.get() + 1)
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# set the context
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self._context_var.set(value)
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