51 lines
2.1 KiB
Python
51 lines
2.1 KiB
Python
 
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import asyncio
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# Defensive cap on concurrent SSE subscribers. Expected load is on the order of
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# ~100 concurrent users; this is set well above that so it never engages under
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# normal use — it exists purely so a runaway/DoS-y number of open connections
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# degrades (new connections fall back to polling, see round_stream()) instead
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# of growing the in-memory subscriber set without bound. Revisit this number if
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# expected concurrency grows well past it.
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MAX_SUBSCRIBERS = 500
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class RoundEventCapacityError(Exception):
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"""Raised by subscribe() when MAX_SUBSCRIBERS is already reached."""
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class RoundEventBroadcaster:
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"""In-process pub/sub so SSE clients (GET /rounds/stream) get pushed a
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notification the instant round/bet/balance state changes, instead of only
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finding out on their next poll. The message carries no payload — it's just
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a "something changed, go refetch" signal; the client re-hits the existing
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per-user REST endpoints (/rounds/current, /users/me, ...) for the actual
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data, so this never needs to know what changed or who's allowed to see it.
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Single-process only (no cross-worker fan-out) — fine for this deployment
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(one uvicorn process, see docker-compose.yml). A multi-worker deployment
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would need a shared channel (e.g. Redis pub/sub) instead.
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"""
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def __init__(self, max_subscribers: int = MAX_SUBSCRIBERS):
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self._subscribers: set[asyncio.Queue] = set()
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self.max_subscribers = max_subscribers
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def subscribe(self) -> asyncio.Queue:
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if len(self._subscribers) >= self.max_subscribers:
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raise RoundEventCapacityError(f"already at the {self.max_subscribers}-subscriber cap")
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queue: asyncio.Queue = asyncio.Queue(maxsize=1)
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self._subscribers.add(queue)
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return queue
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def unsubscribe(self, queue: asyncio.Queue) -> None:
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self._subscribers.discard(queue)
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def publish(self) -> None:
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for queue in self._subscribers:
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if queue.full():
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continue # a not-yet-delivered notification already covers this one
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queue.put_nowait(None)
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broadcaster = RoundEventBroadcaster()
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