Scheduling stress

These host stress cases run the real fsh executable through a pseudoterminal. Nonzero seeds vary process and job actions while keeping wait times limited and checking child cleanup and terminal ownership.

The ordinary workspace test gate runs four fixed regression seeds across these scenarios:

• foreground pipeline cancellation with two to four process-group members, zero to two stop/resume cycles, optional job-table observations, and foreground, background, or stopped cancellation placement;
• repeated foreground/background job-control cycles;
• concurrent background completions released in different orders; and
• interactive exit while running and stopped jobs remain live.

The host kernel still schedules threads and processes. Replaying a seed repeats the generated choices and assertions, but not necessarily the same wall-clock timing.

Run a campaign

After building Flash, run 64 generated seeds per scenario from the repository root with the selected candidate runtime:

components/flash/target/debug/fsh components/flash/scheduling/run-campaign.fsh

The first argument selects a positive case count up to 4,096. The optional second argument selects a new result directory, and the optional third argument sets a nonzero decimal or 0x-prefixed campaign seed:

components/flash/target/debug/fsh components/flash/scheduling/run-campaign.fsh \
  256 /path/to/new-results 0x4f3c2b1a098765ef

When no seed is supplied, the runner reads one from the host random source. It prints the chosen seed before starting. A result directory must not already exist, preventing separate runs from silently sharing evidence.

The default result path is a unique, ignored directory under scheduling/campaigns/. Every result retains:

• manifest.txt, with the campaign seed, bounds, host and tool versions, replay command, timestamps, and result; and
• output.log, with every exact scenario seed and the complete test output.

Replay a failure

Replay the complete campaign with the command recorded in its manifest. To run only one exact seed reported immediately before a failure:

FLASH_PTY_STRESS_SEEDS=0x0123456789abcdef \
  cargo test -p flash-cli --test pty stress_ -- \
  --nocapture --test-threads=1

Replace stress_ with the complete failing test name to isolate one scenario. Retain the failed campaign directory until the result has been reproduced and reduced to a fixed regression seed or a narrower deterministic test.

Evidence boundary

The PTY harness is supported on Linux and macOS hosts. It exercises real host process groups, signal delivery, terminal ownership, pipelines, cancellation, and job notices. It does not establish equivalent FlashOS target behavior. Redox target builds prove compilation separately, while image/QEMU or hardware qualification owns target runtime claims. Campaign completion is bounded evidence for the exercised seeds and scenarios, not proof that scheduling defects are absent.