IOSim: timeout can return while its assasin threas is still ailve

オープン
  • 何か問題がありますか？
#271 コメント 3 件 リアクション 0 件 担当者 0 名 GitHub で見る

まだ誰も着手していません。

評価

難易度
4/5
見積もり時間
3〜5日
初心者へのやさしさ
48/100
issue の種類
バグ
明瞭さ
おおむね明確
活発さ
活発
技術スタック
haskell
領域
testing

調査の方向性

Start by reading the IOSim implementation of timeout, its assassin thread, and the runSimStrictShutdown checks; the issue gives six reproductions using threadDelay, yield, and STM. Trace the tie cases where the assassin remains queued or has a pending ThreadKilled, then verify that all scenarios finish without FailureSloppyShutdown while preserving their stated results.

索引モデルが issue の本文から書いたものです。

説明

bug

Describe the bug
timeout can return while its assassin thread is still alive, so runSimStrictShutdown fails with FailureSloppyShutdown

In IOSim, timeout forks an assassin thread when its timer fires. If the action finishes at the same moment the timeout expires, timeout can return while the assassin is still alive. Any simulation run with runSimStrictShutdown then fails with FailureSloppyShutdown.

The result itself is correct: the leftover assassin never throws. But in simulations the action often finishes exactly at the deadline, so this makes strict shutdown unusable for code that uses timeout. GHC has no equivalent of the strict-shutdown check, so the problem only shows up in the simulator.

To Reproduce

Each scenario run with runSimStrictShutdown:

Scenario Code Result
a. timer never fires timeout 1 (threadDelay 0.5) Just ()
b. timeout wins timeout 1 (threadDelay 2) Nothing
c. tie, action finishes first timeout 1 (threadDelay 1) FailureSloppyShutdown
c′. c, then yield timeout 1 (threadDelay 1) <* yield FailureSloppyShutdown
d. tie, action yields before finishing timeout 1 (threadDelay 1 >> atomically (pure ())) FailureSloppyShutdown
d′. d, then yield timeout 1 (threadDelay 1 >> atomically (pure ())) <* yield Just ()
  • Case c: the assassin hasn't run yet. At 1s the delay timer wakes the main thread, and the timeout timer forks the assassin, which is queued behind main.
    Main leaves the TimeoutFrame, takes the lock and finishes. The assassin is still in the run queue, so TraceMainReturn lists it as running. A yield
    doesn't help: the assassin's tryPutTMVar commit yields too, so main finishes before the assassin exits.
  • Case d: the assassin holds the lock but hasn't thrown yet. The frame exit killThreads it. Killing an unmasked thread doesn't block; it only replaces the
    thread's next action with Throw ThreadKilled. So the assassin isn't dead yet when main finishes. One yield lets it terminate, which is why d′ passes.
主要言語
Haskell
スター
57
フォーク
25
30日以内にマージされた PR はありません

環境構築

はじめの一歩

  1. issue を最後まで読み、次にプロジェクトのコントリビューションガイドを読みます。
  2. 着手することを issue にコメントします — 二人が同じ作業をするのを防げます。
  3. リポジトリをフォークし、ブランチを切って変更します。
  4. issue 番号を参照したプルリクエストを送ります。

IntersectMBO/io-sim のほかの issue

IntersectMBO/io-sim の issue をすべて見る

似ている issue

Haskell の issue をもっと見る

新しい issue をメールで受け取る

初心者向けの GitHub issue を短くまとめたダイジェスト。