Sandbox_LongRunningScript_TimesOut and Sandbox_InfiniteLoop_CancelledByToken
armed a CancellationTokenSource for a fixed 100 ms / 500 ms and hoped it
expired while the script body was still running. That is a race between a
fixed timer and a fixed amount of work, not a synchronization, and it is
wrong in both directions.
Too slow a timer relative to the work and the script FINISHES first, so
nothing is cancelled and ThrowsAnyAsync fails with "No exception was thrown".
Measured on this machine: the bounded 100M-iteration loop takes 298 ms
against the 100 ms pin — a 3x margin that a faster host closes, and that any
move off the scripting default OptimizationLevel.Debug would close outright.
Reproduced deterministically by shrinking the loop to 1M iterations: it ran
in 76 ms and the test failed with exactly that message while all 27 siblings
passed.
Too fast a timer and the token is already cancelled before the body is
entered — Roslyn's runner throws OperationCanceledException up front
(verified with a pre-cancelled token) — so the test goes GREEN without the
script's own in-loop ThrowIfCancellationRequested ever being reached. That
vacuous pass is the worse half: it asserts nothing while looking healthy.
Both now cancel deterministically. The script invokes an Action handed in
through Parameters from inside its own loop; when that call returns the token
is already cancelled ON THE SAME THREAD, so the next in-loop check is
guaranteed to observe it, with ~10,000 checks still ahead of it. No wall
clock, no host-speed or scheduler dependence — and the 600 ms of sleeping
goes away. Sandbox_UncancelledScript_RunsToCompletion is added as the
negative control: the same script with the signal wired to a no-op must run
every iteration and return the closed-form sum, which is what establishes
that the sibling's OCE is caused by the cancellation.
Verified: the injection that killed the old test passes with the fix, and
suppressing the cancellation entirely still fails it with the identical
message, so the claim is unchanged in force. Test-only; the sandbox's
cancellation behaviour is correct as written.
Joseph Doherty