Coalesce adjacent free spans without corrupting the index
The free-span list merges with the previous range but forgets the next range, leaving overlapping entries that can be allocated twice.
- Focused work estimate
- 4h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Data structures · Invariants · Property testing
Estimated field mix
- Systems programming75%
- Quality engineering25%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional telemetry collector copies decoded packet fields into a small native arena. The prototype misaligns wide values and reuses memory while readers still hold views. Create a local Rust crate or C library with generated byte fixtures; no device traffic or production allocator replacement is supplied.
Setup prerequisites
- Pointers and slices
- Integer overflow
- Memory alignment
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Free spans remain ordered, nonoverlapping, and maximal
- Freeing in any order yields the same canonical span set
- Double-free and out-of-range spans are rejected
Implementation constraints
- Update the span index under one mutation boundary and preserve the arena on validation failure.
Verification to include
- Free three adjacent blocks in all six orders and compare the final index.
- Attempt an overlapping release and prove no index entry changes.
Deliverables
- Canonical coalescing algorithm and permutation tests
Rollout and recovery
Run shadow invariant checks in the local benchmark before using reclaimed spans.
Value of the work
For the engineer: Practice representation invariants, lifetimes, unsafe-boundary review and memory diagnostics.
For the team: Review a component whose allocation failures and corruption cases are explicit before reuse in latency-sensitive code.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.