39 lines
1.4 KiB
Python
39 lines
1.4 KiB
Python
"""Bound readiness work even when a synchronous dependency ignores its timeout."""
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import asyncio
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import time
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class Readiness:
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def __init__(self, probe, *, timeout=3, cache_seconds=5):
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self.probe = probe
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self.timeout = timeout
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self.cache_seconds = cache_seconds
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self.lock = asyncio.Lock()
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self.running = None
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self.until = 0.0
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self.ok = False
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@staticmethod
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def consume(task):
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# A request can time out or disconnect before the synchronous probe ends.
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# Retrieve late exceptions without logging dependency messages/secrets.
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if not task.cancelled():
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task.exception()
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async def check(self):
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async with self.lock:
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if time.monotonic() < self.until:
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return self.ok
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if self.running is None or self.running.done():
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self.running = asyncio.create_task(asyncio.to_thread(self.probe))
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self.running.add_done_callback(self.consume)
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try:
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# Cancelling a to_thread await does not stop its OS thread. Keep
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# the task alive so subsequent requests reuse the same probe.
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await asyncio.wait_for(asyncio.shield(self.running), self.timeout)
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self.ok = True
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except Exception:
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self.ok = False
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self.until = time.monotonic() + self.cache_seconds
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return self.ok
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