rust-development

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name: rust-development description: Hub skill for Rust development. Covers the full workflow from profiling → performance diagnosis → CPU/memory optimization → parallelism. Routes to the right specialist skill based on the symptom. Links all four Rust skills: rust-profiling, rust-perf-tuning, rust-memory-optimization, rust-parallel-processing. paths: "**/*.rs" metadata: type: feedback

Rust Development Hub

This is a routing and overview skill. It maps symptoms to the right specialist skill and provides the overall Rust optimization workflow.

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Workflow: Measure → Diagnose → Fix → Verify

1. MEASURE        → rust-profiling
   Flamegraph, heaptrack, perf stat. Establish baseline numbers.
   Never skip. Never optimize without a number to beat.

2. DIAGNOSE       → rust-profiling + rust-perf-tuning + rust-memory-optimization
   Read the flamegraph. Is the hotspot:
   ├── CPU-bound, single-threaded? → rust-perf-tuning
   ├── Memory / allocation churn?  → rust-memory-optimization
   ├── CPU-bound but underutilized cores? → rust-parallel-processing
   └── I/O-bound? → tokio async patterns (rust-parallel-processing §2)

3. FIX            → specialist skill
   Apply the fix from the relevant specialist skill.
   Keep changes small — one variable at a time.

4. VERIFY         → rust-profiling
   Re-run the same benchmark/profiler. Confirm numbers improved.
   If not: revert, re-diagnose. Don't stack guesses.

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Skill Map: Which Skill for Which Symptom

Symptom	Skill
"I need a flamegraph"	[[rust-profiling]]
"Find the CPU hotspot"	[[rust-profiling]]
"Benchmark before/after"	[[rust-profiling]]
"Hot loop is slow"	[[rust-perf-tuning]]
"HashMap is too slow"	[[rust-perf-tuning]] (FxHashMap)
"Enable LTO or PGO"	[[rust-perf-tuning]]
"High RSS / OOM"	[[rust-memory-optimization]]
"Allocation churn in heaptrack"	[[rust-memory-optimization]]
"Bounded ring buffer for telemetry"	[[rust-memory-optimization]]
"Custom allocator (mimalloc, jemalloc)"	[[rust-memory-optimization]]
"Memory leak"	[[rust-memory-optimization]]
"par_iter() / rayon"	[[rust-parallel-processing]]
"Async fan-out with tokio"	[[rust-parallel-processing]]
"GPU compute (wgpu, cudarc)"	[[rust-parallel-processing]]
"ML inference in Rust (candle)"	[[rust-parallel-processing]]
"Multi-machine (tonic, MPI, ractor)"	[[rust-parallel-processing]]
"SIMD / auto-vectorization"	[[rust-parallel-processing]]

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Rust Specialist Skills

Skill	Focus
[[rust-profiling]]	Flamegraphs (cargo-flamegraph, samply), heaptrack, perf, criterion. Collect data first — every other skill depends on this.
[[rust-perf-tuning]]	CPU throughput: data-oriented design, FxHashMap, LTO/PGO, SIMD baselines, bounds check elimination, hot-loop restructuring.
[[rust-memory-optimization]]	RSS reduction: compact types, custom allocators, arenas, bounded ring buffers, zero-copy (bytes, memmap2, zerocopy), leak detection (dhat, LeakSanitizer).
[[rust-parallel-processing]]	Scaling: rayon (data parallelism), tokio (async tasks), SIMD, GPU (wgpu/cudarc/candle), multi-machine (tonic/MPI/ractor/DataFusion).

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Essential Cargo Config

# .cargo/config.toml — apply to all builds in this workspace
[build]
rustflags = ["-C", "target-cpu=native"]  # enables AVX2, SSE4.2 auto-vectorization

[profile.release]
lto = "thin"          # ~5-10% speedup from cross-crate inlining
codegen-units = 1     # single CGU → more inlining opportunities
opt-level = 3         # default for release

[profile.profiling]   # flamegraph-friendly: fast but readable symbols
inherits = "release"
debug = 1             # line tables only (small binary, readable stacks)

Key Profiling Commands (quick reference)

# CPU flamegraph
cargo flamegraph --bin mybinary -- args
# or: samply record ./target/release/mybinary

# Heap profile
heaptrack ./target/release/mybinary
heaptrack_print heaptrack.mybinary.PID.zst | head -40

# Allocation benchmark
cargo bench -- --profile-time=5

# tokio async task visibility
cargo install tokio-console && tokio-console

Dependency Version Hygiene

Check for outdated dependencies with:

cargo install cargo-outdated   # one-time install
cargo outdated                 # show all deps behind latest
cargo outdated --root-deps-only  # only direct deps (less noise)

When cargo build resolves a lower version than available, it prints:

Adding tokio-tungstenite v0.24.0 (available: v0.29.0)

Always use the latest available version — update Cargo.toml to the version shown in parentheses.

Known breaking changes between major versions

Crate	Old version	New version	Breaking change
reqwest	0.12	0.13	Feature rustls-tls renamed to rustls
tokio-tungstenite	0.24	0.29	Message::Text(String) → Message::Text(Utf8Bytes), Message::Binary(Vec<u8>) → Message::Binary(Bytes) — both accept .into() from the old types
chrono	any	0.4	local-offset feature doesn't exist on older pinned versions; use serde feature instead and call Local::now() directly

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Essential Crate Quick Reference

Crate	Layer	Use for
rayon	CPU parallel	Data parallelism — par_iter(), join(), scope()
tokio	Async	I/O-bound + task fan-out, JoinSet, Semaphore
wide	SIMD	Manual AVX2 without nightly (f32x8, u8x32)
crossbeam	Concurrent	Bounded channels, deques, CachePadded
wgpu	GPU	Cross-platform compute (Vulkan/Metal/DX12)
cudarc	GPU	NVIDIA CUDA — maximum GPU performance
candle	GPU/ML	Pure-Rust inference, HuggingFace model weights
tonic	Network	gRPC — cross-language RPC
tarpc	Network	Rust-only RPC — simpler, no protobuf
mpi	HPC	Multi-machine numerical — allreduce, scatter
ractor	Distributed	Erlang-style actors — fault-tolerant stateful services
datafusion	Analytics	Distributed SQL over Parquet / Arrow
compact_str	Memory	Drop-in String replacement — inline ≤ 24B
mimalloc	Memory	Faster global allocator
bumpalo	Memory	Per-scope arena — O(1) alloc, O(1) free all
dhat	Memory	CI heap assertions — catch leaks at PR time
criterion	Bench	Statistical micro-benchmarks