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Remove graph_lock from the _schema_at hot path

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評估

難度
5/5
預估耗時
一週以上
新手友好度
35/100
Issue 類型
重構
描述清晰度
需要釐清
活躍度
活躍
技術堆疊
julia
領域
performance

研究方向

Start in src/runtime.jl at _schema_at, then inspect _build_schema_at and the accesses to spec.subschemas and spec.graph_lock. Compare the precomputation and immutable-cache options described in the issue, including their interaction with generated descriptors and concurrent decoders. Done means removing the lock from the lookup hot path without unsafe concurrent Dict reads.

由索引模型根據 Issue 內容生成。

描述

Follow-up from #126, raised in review.

_schema_at (src/runtime.jl) now caches subschema views in spec.subschemas, guarded by spec.graph_lock:

cached = lock(() -> get(spec.subschemas, key, nothing), spec.graph_lock)
cached === nothing || return cached
schema = _build_schema_at(spec, descriptor, direction)
lock(() -> (spec.subschemas[key] = schema), spec.graph_lock)

Every lookup takes the lock once, and the first lookup of a key takes it twice. Before #126 this path was lock-free once the graph existed, but it rebuilt the view on every call. Uncontended, the lock costs about 200 ns per call. Under multi-threaded decoding it serializes lookups.

The lock is required: subschemas is a plain Dict written by concurrent decoders, so the read cannot simply drop it.

Options:

  • Precompute views for all known descriptors when the graph is built. Descriptors are per-call-site constants in generated code, so this needs codegen to register them.
  • Keep an immutable cache and swap it atomically on miss. Reads become lock-free, and a miss copies the cache.
主要語言
Julia
星號
56
分支
16
平均合併
22 小時 43 分鐘
30 天內合併 PR
6

環境準備

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從這裡開始

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  3. Fork 儲存庫,在一個分支上完成修改。
  4. 送出 Pull Request,並在描述裡引用這個 Issue 編號。

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