@@ -0,0 +1,205 @@ |
| 1 | +"""LRU cache for warm differential backends. |
| 2 | + |
| 3 | +The point of the daemon is keeping backends loaded across requests. |
| 4 | +This module owns the cache: keyed by an immutable identity tuple over |
| 5 | +the ModelSpec fields that determine backend identity, capped at a |
| 6 | +configurable size, evicts least-recently-used on overflow with proper |
| 7 | +``close()`` so weights actually get freed. |
| 8 | + |
| 9 | +The cache is **process-local** — there's no on-disk component. Restart |
| 10 | +the daemon and the cache resets cold. That's intentional: warm-backend |
| 11 | +caching is a memory tradeoff, and persisting weights to disk would |
| 12 | +duplicate what HuggingFace's own cache already does at the file level. |
| 13 | +""" |
| 14 | + |
| 15 | +from __future__ import annotations |
| 16 | + |
| 17 | +import logging |
| 18 | +import threading |
| 19 | +from collections import OrderedDict |
| 20 | +from collections.abc import Hashable |
| 21 | +from dataclasses import dataclass |
| 22 | +from pathlib import Path |
| 23 | + |
| 24 | +from dlm_sway.core.errors import SwayError |
| 25 | +from dlm_sway.core.model import ModelSpec |
| 26 | +from dlm_sway.core.scoring import DifferentialBackend |
| 27 | + |
| 28 | +_LOG = logging.getLogger(__name__) |
| 29 | + |
| 30 | + |
| 31 | +def cache_key_for(spec: ModelSpec) -> tuple[Hashable, ...]: |
| 32 | + """Identity tuple for a ModelSpec. |
| 33 | + |
| 34 | + Two ModelSpecs that differ only in fields that don't affect the |
| 35 | + loaded backend (e.g. ``trust_remote_code`` on the same already- |
| 36 | + cached model) hash to the same key. We're conservative — any field |
| 37 | + that touches model identity (``base``, ``adapter``, ``dtype``, |
| 38 | + ``device``, ``kind``) goes into the key. Path normalization |
| 39 | + happens upstream in ModelSpec's validator. |
| 40 | + """ |
| 41 | + return ( |
| 42 | + spec.kind, |
| 43 | + spec.base, |
| 44 | + str(spec.adapter) if spec.adapter is not None else None, |
| 45 | + spec.dtype, |
| 46 | + spec.device, |
| 47 | + ) |
| 48 | + |
| 49 | + |
| 50 | +@dataclass(frozen=True, slots=True) |
| 51 | +class CachedBackend: |
| 52 | + """One entry in the cache. Frozen — fields don't mutate after load. |
| 53 | + |
| 54 | + ``key`` is the identity tuple; ``backend`` is the live object; |
| 55 | + ``model_spec`` is kept for introspection (``GET /health`` lists |
| 56 | + the loaded models so users can see what's warm). |
| 57 | + """ |
| 58 | + |
| 59 | + key: tuple[Hashable, ...] |
| 60 | + backend: DifferentialBackend |
| 61 | + model_spec: ModelSpec |
| 62 | + load_seconds: float |
| 63 | + |
| 64 | + |
| 65 | +class BackendCache: |
| 66 | + """LRU cache of differential backends. |
| 67 | + |
| 68 | + Thread-safe via a single internal lock. The cache contract: |
| 69 | + |
| 70 | + 1. ``get_or_load(spec)`` returns a backend; on miss, builds it |
| 71 | + (paying the load cost) and admits to the cache. |
| 72 | + 2. On overflow (``len > max_size``), evict LRU. Eviction calls |
| 73 | + ``backend.close()`` if the backend implements it; otherwise |
| 74 | + drops the reference and lets GC handle it. |
| 75 | + 3. ``get_or_load`` is single-flight per key — concurrent requests |
| 76 | + for the same model wait on the loader thread instead of |
| 77 | + building the backend twice. |
| 78 | + """ |
| 79 | + |
| 80 | + def __init__(self, max_size: int = 2) -> None: |
| 81 | + if max_size < 1: |
| 82 | + raise ValueError(f"max_size must be >= 1; got {max_size}") |
| 83 | + self._max = int(max_size) |
| 84 | + self._entries: OrderedDict[tuple[Hashable, ...], CachedBackend] = OrderedDict() |
| 85 | + self._lock = threading.RLock() |
| 86 | + # Per-key load locks so concurrent requests for the same model |
| 87 | + # serialize at the loader instead of building twice. |
| 88 | + self._key_locks: dict[tuple[Hashable, ...], threading.Lock] = {} |
| 89 | + |
| 90 | + @property |
| 91 | + def max_size(self) -> int: |
| 92 | + return self._max |
| 93 | + |
| 94 | + def loaded_keys(self) -> list[tuple[Hashable, ...]]: |
| 95 | + """Snapshot of currently-cached keys, MRU last. Used by /health.""" |
| 96 | + with self._lock: |
| 97 | + return list(self._entries.keys()) |
| 98 | + |
| 99 | + def loaded_specs(self) -> list[ModelSpec]: |
| 100 | + """Snapshot of currently-cached model specs, MRU last.""" |
| 101 | + with self._lock: |
| 102 | + return [entry.model_spec for entry in self._entries.values()] |
| 103 | + |
| 104 | + def get_or_load(self, spec: ModelSpec, *, adapter_path: Path | None = None) -> CachedBackend: |
| 105 | + """Return a cached backend for ``spec`` or build + admit one. |
| 106 | + |
| 107 | + ``adapter_path`` overrides ``spec.adapter`` for the build call — |
| 108 | + mirrors the upstream :func:`dlm_sway.backends.build` contract |
| 109 | + so callers handing in a separately-resolved adapter (e.g. via |
| 110 | + the dlm bridge) don't have to construct a copy of the spec. |
| 111 | + Cache key uses ``spec.adapter``, NOT the override; if you want |
| 112 | + a different adapter to cache distinctly, pass a spec that |
| 113 | + encodes it. |
| 114 | + """ |
| 115 | + key = cache_key_for(spec) |
| 116 | + |
| 117 | + # Fast path — spec already cached. |
| 118 | + with self._lock: |
| 119 | + entry = self._entries.get(key) |
| 120 | + if entry is not None: |
| 121 | + # Touch LRU position. |
| 122 | + self._entries.move_to_end(key) |
| 123 | + return entry |
| 124 | + key_lock = self._key_locks.setdefault(key, threading.Lock()) |
| 125 | + |
| 126 | + # Slow path — single-flight load. |
| 127 | + with key_lock: |
| 128 | + with self._lock: |
| 129 | + # Recheck after acquiring the load lock — another thread |
| 130 | + # may have completed the load while we waited. |
| 131 | + entry = self._entries.get(key) |
| 132 | + if entry is not None: |
| 133 | + self._entries.move_to_end(key) |
| 134 | + return entry |
| 135 | + |
| 136 | + entry = _build_entry(spec, key=key, adapter_path=adapter_path) |
| 137 | + |
| 138 | + with self._lock: |
| 139 | + # Evict to fit before admitting; ensures we never spike |
| 140 | + # over max_size + 1 between admission and eviction. |
| 141 | + while len(self._entries) >= self._max: |
| 142 | + self._evict_lru_locked() |
| 143 | + self._entries[key] = entry |
| 144 | + self._entries.move_to_end(key) |
| 145 | + return entry |
| 146 | + |
| 147 | + def evict_all(self) -> None: |
| 148 | + """Close every backend. Called on daemon shutdown.""" |
| 149 | + with self._lock: |
| 150 | + keys = list(self._entries.keys()) |
| 151 | + for k in keys: |
| 152 | + self._evict_locked(k) |
| 153 | + |
| 154 | + # -- internals ----------------------------------------------------- |
| 155 | + |
| 156 | + def _evict_lru_locked(self) -> None: |
| 157 | + # Caller holds self._lock. ``OrderedDict.__iter__`` yields |
| 158 | + # insertion order; LRU is the first key. |
| 159 | + if not self._entries: |
| 160 | + return |
| 161 | + lru_key = next(iter(self._entries)) |
| 162 | + self._evict_locked(lru_key) |
| 163 | + |
| 164 | + def _evict_locked(self, key: tuple[Hashable, ...]) -> None: |
| 165 | + # Caller holds self._lock. |
| 166 | + entry = self._entries.pop(key, None) |
| 167 | + if entry is None: |
| 168 | + return |
| 169 | + # Backends carry a ``close()`` when they own GPU memory or |
| 170 | + # network connections (HF, MLX, API). Dummy doesn't — |
| 171 | + # so don't require it. Failure during close is logged and |
| 172 | + # swallowed: a daemon stays up even if one backend's close() |
| 173 | + # raises. |
| 174 | + close = getattr(entry.backend, "close", None) |
| 175 | + if callable(close): |
| 176 | + try: |
| 177 | + close() |
| 178 | + except Exception as exc: # noqa: BLE001 |
| 179 | + _LOG.warning("backend close raised on eviction: %s", exc) |
| 180 | + self._key_locks.pop(key, None) |
| 181 | + |
| 182 | + |
| 183 | +def _build_entry( |
| 184 | + spec: ModelSpec, |
| 185 | + *, |
| 186 | + key: tuple[Hashable, ...], |
| 187 | + adapter_path: Path | None, |
| 188 | +) -> CachedBackend: |
| 189 | + """Materialize a backend from a spec, timing the load.""" |
| 190 | + import time |
| 191 | + |
| 192 | + from dlm_sway.backends import build as build_backend |
| 193 | + |
| 194 | + started = time.monotonic() |
| 195 | + try: |
| 196 | + backend = build_backend(spec, adapter_path=adapter_path) |
| 197 | + except SwayError: |
| 198 | + raise |
| 199 | + except Exception as exc: # noqa: BLE001 — surface load failures as SwayError |
| 200 | + raise SwayError( |
| 201 | + f"backend load failed for kind={spec.kind} base={spec.base!r}: " |
| 202 | + f"{type(exc).__name__}: {exc}" |
| 203 | + ) from exc |
| 204 | + elapsed = time.monotonic() - started |
| 205 | + return CachedBackend(key=key, backend=backend, model_spec=spec, load_seconds=elapsed) |