# `Lockstep.Strategy.PCT`
[🔗](https://github.com/b-erdem/lockstep/blob/v0.1.0/lib/lockstep/strategy/pct.ex#L1)

Probabilistic Concurrency Testing.

Burckhardt, Kothari, Musuvathi, Nagarakatte. "A Randomized Scheduler
with Probabilistic Guarantees of Finding Bugs", ASPLOS 2010.

Each managed process gets a random initial priority. On every step the
highest-priority *enabled* (i.e. ready) process runs. Before the test
starts, `d - 1` step indices are drawn uniformly from `[1, max_steps]`;
at each, the priority of whichever process *would* run next is demoted
to a fresh, lower-than-everyone priority. This produces a randomized
schedule that hits any bug of depth `d` with probability ≥ `1 / (n · k^(d-1))`
per iteration.

## Options

  * `:seed`       — RNG seed (required)
  * `:max_steps`  — total scheduling steps (required)
  * `:bug_depth`  — `d` in PCT terms (default 3)
  * `:high_prio_max` — upper bound for initial priorities (default 1_000_000)

Note: the algorithm ships PCT as described. For liveness add `Lockstep.Strategy.FairPCT`.

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*Consult [api-reference.md](api-reference.md) for complete listing*