Stacks & Queues

Bound it whenever arrivals are not limited by something else, because an unbounded in-memory queue converts a slow consumer into a dead process. A bounded queue must then report refusal explicitly on enqueue — never accept-and-discard — so every caller owns what happens to the rejected ticket.

A single first-in-first-out queue is fair to jobs, not to people: one user's five-hundred-page batch delays everyone behind it. Round-robin over per-user queues makes a job's wait depend on how many users are active, not on one user's backlog.

All the candidates are constant time per operation, so the decision is memory under worst-case input versus who has to maintain the clever version. Bound the stack depth first; if the simple paired-value design then fits the cap, standardise on it.

On memory-capped hardware, reject the push and make the rejection visible. A fixed capacity turns an unpredictable out-of-memory failure into a local, testable policy — provided the caller is told and someone has decided which readings may be lost.