[PointKernel]

Description

Closes #11136.

This PR migrates the host rehash and rehash_async APIs from cuCollections static_set to fixed_capacity_set, reusing the shared open-addressing implementation. As with fixed_capacity_map, the overloads taking a new capacity are only available for dynamic capacity.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[PointKernel]

/ok to test b5cb27b

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No actionable comments were generated in the recent review.

Summary

Summary by CodeRabbit

• New Features
  • Added synchronous and asynchronous rehashing for fixed-capacity sets. Dynamic-capacity sets can also rehash to a requested capacity.
  • Rehashing preserves stored keys; capacity changes are reflected in the set.

fixed_capacity_set adds synchronous and asynchronous rehash operations. Dynamic-capacity sets can request a minimum capacity. Tests check overload availability, capacity results, and key preservation.

Changes: fixed_capacity_set rehash

Layer / File(s)	Summary
Rehash overloads cudax/include/cuda/experimental/__cuco/fixed_capacity_set.cuh	Adds synchronous and asynchronous rehash operations. Capacity-taking overloads are available for dynamic-capacity sets and use the smallest valid capacity at least as large as requested.
Rehash availability and behavior cudax/test/cuco/fixed_capacity_set/test_capacity.cu, cudax/test/cuco/fixed_capacity_set/test_insert_and_contains.cu	Adds compile-time checks for the overloads and runtime checks for capacity and key preservation after rehashing.

Assessment against linked issues

Objective	Addressed	Explanation
Migrate host rehash APIs to fixed_capacity_set and add corresponding tests [#11136]	✅

Suggested reviewers: jacobfaib

Change: Feature

Merge Risk: Minimal · up to b5cb2

This adds synchronous and asynchronous rehash operations to the experimental fixed_capacity_set, with capacity-taking forms limited to dynamic-capacity sets. No concrete merge-blocking risk was identified, and tests cover the new overloads.

Security architecture risk: Low · up to b5cb2

A kernel-launch failure during the newly exposed rehash operation can discard the set’s previous contents without rollback. The supported consequence is local state loss; the inspected change does not establish a privilege escalation or cross-service attack path.

Retained concerns

• Low · reliability · inferred: The newly public set rehash path publishes empty replacement storage before launching reinsertion. If launch preparation or submission throws before reinsertion is enqueued, unwinding releases the old storage without restoring it, so retrying cannot recover the previous keys. This failure behavior predates the PR in the shared map implementation but becomes newly reachable through fixed_capacity_set. No contents-preservation guarantee on failure is documented.

Security review details

Security Blast Radius

• inferred — The supported failure consequence is loss of the affected set’s keys and invalidation of its borrowed storage references. No supplied downstream caller establishes a broader tenant, service, or security-policy consequence.

Trust Boundaries and Controls

• observed — The routed has_capacity_rehash symbol is a compile-time test detection trait used by static assertions, not an executable request handler. The actual public operations act on a caller-owned set and rely on documented exclusive access and borrowed-reference lifetime obligations.

Resilience and Maintainability Implications

• inferred — Failures before the storage swap retain the original published storage. After the swap, there is no rollback around the potentially throwing launch. Existing map reuse and the lack of a strong exception guarantee limit the concern to newly exposed, destructive recovery semantics rather than a demonstrated authorization or isolation failure.

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Recent review info

Run configuration

• Source mode: Auto
• Repository: NVIDIA/cccl
• Branch: main
• File: .coderabbit.yaml
• Commit: ae772fa
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Enterprise
• Run ID: 6ade8776-df1a-4257-821b-3a1dc9418031

Commits

Reviewing files that changed from the base of the PR and between ae772fa and b5cb27b.

Files selected for processing: 3

• cudax/include/cuda/experimental/__cuco/fixed_capacity_set.cuh
• cudax/test/cuco/fixed_capacity_set/test_capacity.cu
• cudax/test/cuco/fixed_capacity_set/test_insert_and_contains.cu

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