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Determinant and Inverse return wrong values when called from more than one thread

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@Rafael-SOWNet 已經在處理了。

開始於 2026年9月9日。

  • #41 來自 @Rafael-SOWNet —— 未關閉

評估

難度
4/5
預估耗時
3-5 天
新手友好度
35/100
Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
停滯
技術堆疊
csharp
領域
performance

研究方向

先從 SquareMatrixFactory<T, TWrapper>.GetMatrix 和 ExpressionCompiler<T, TWrapper>.storage 開始，然後使用 Parallel.For 重現回報的行列式/反矩陣失敗，包括冷快取情況。完成標準是並行矩陣操作回傳經過循序驗證的值，且不會出現集合例外或共用緩衝區損毀。

由索引模型根據 Issue 內容生成。

描述

Two process-wide statics are read and written with no synchronisation, so matrix operations called from more than one thread return wrong numbers. Nothing throws, nothing is malformed, and no result looks suspicious.

I found this from the other side: AngouriMath uses GenTensor for its symbolic matrices, and a determinant computed on a background thread was coming back numerically wrong. AngouriMath's issue is #1219.

1. The scratch-matrix pool

SquareMatrixFactory<T, TWrapper>.GetMatrix hands every caller the same GenTensor for a given size, and the caller then writes into it — Inversion.GetCofactorMatrix(t, temp, ...) fills the matrix it is given. Two threads taking a determinant or an inverse of the same size get the same buffer and overwrite each other's minors between the write and the read.

Sixty 5×5 int matrices, each computed once sequentially for truth and then rebuilt and recomputed under Parallel.For:

DeterminantLaplace    53 of 60 disagree
Adjoint               60 of 60 disagree

Around 10 ms, every run. This is not a rare interleaving, it is the normal case.

DeterminantGaussianSafeDivision is unaffected — it works on its own copy and never asks the pool for anything.

The lock inside GetMatrix does not help and is itself incomplete: the list is indexed after the lock is released, so a concurrent Add can reallocate the backing array underneath the reader.

2. The compiled-operation cache

ExpressionCompiler<T, TWrapper>.storage is a plain Dictionary, written by whichever thread first asks for a given (operation, rank, parallel). Dictionary<,> is documented as safe for concurrent readers only while nobody is writing.

Reached cold from several threads it fails with the runtime's own diagnostic:

System.InvalidOperationException: Operations that change non-concurrent collections must
have exclusive access. A concurrent update was performed on this collection and corrupted
its state. The collection's state is no longer correct.
...
The given key '(Subtraction, 1, False)' was not present in the dictionary.

Worth noting that this one hides easily. My first test computed its expected values sequentially and only then went parallel, which populated every key before the threads started — the cache holds a handful of entries, so a warm-up makes the defect invisible and the test passes against the broken code.

Fix

I have opened a PR. Both are small: [ThreadStatic] for the pool, since a scratch buffer has nothing to share between threads, and ConcurrentDictionary for the cache. The Laplace determinant comes out about 5% faster, because the pool is now taken once at the top of the recursion instead of re-checked and re-indexed at every one of its n! nodes.

主要語言
C#
星號
52
分支
6
30 天內沒有已合併 PR

環境準備

這個專案沒有提供開發容器、Dockerfile 或貢獻指南，環境需要你自己搭建：先看它的 README，通用步驟見我們的新手貢獻指南。

從這裡開始

  1. 先讀完整個 Issue，再讀專案的貢獻指南。
  2. 在 Issue 下留言說明你要接手 —— 這能避免兩個人做同樣的事。
  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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