39 lines
1.7 KiB
Python
39 lines
1.7 KiB
Python
"""Best-effort accessors for the single-writer stream fence.
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The fence lives on ``AIAgent`` (``_claim_stream_writer`` / ``_stream_writer_is_current``) but is
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used from other streaming modules. Calling it directly would turn an *additive* safety net into a
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fatal AttributeError on a partially-updated checkout, hot-reloaded gateway, duck-typed agent, or
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test double (a cron job died this way). The fence may only drop a *provably* superseded stream,
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never the sole writer, so when it is unavailable or raises the degradation is "no fence".
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"""
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from __future__ import annotations
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import logging
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from typing import Any
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logger = logging.getLogger(__name__)
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def claim_stream_writer(agent: Any) -> int:
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"""Claim the delta sink for this stream attempt; ``0`` (never fenced) when the agent lacks the fence or the claim raised."""
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return _fence_call(agent, "_claim_stream_writer", int, 0, "claim failed; proceeding unfenced")
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def stream_writer_is_current(agent: Any, token: int) -> bool:
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"""True when ``token`` is still the active writer; a falsy token or a fence-less agent cannot prove supersession, so True."""
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if not token:
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return True
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return _fence_call(agent, "_stream_writer_is_current", bool, True, "is_current check failed; treating as current", token)
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def _fence_call(agent: Any, name: str, cast, fallback, failure_note: str, *args):
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"""Call ``agent.<name>(*args)`` when it exists; ``fallback`` when missing or raising (logged at debug)."""
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fn = getattr(agent, name, None)
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if callable(fn):
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try:
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return cast(fn(*args))
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except Exception:
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logger.debug("stream single-writer: %s", failure_note, exc_info=True)
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return fallback
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