Juce review

Skill kunitoki/sonic-skills/skills/juce-review

Modular Markdown-based audio skills for AI agents and developers, covering signal processing, synthesis, effects, analysis, and spatial audio.

Install

npx -y skills add kunitoki/sonic-skills --skill juce-review

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One thing to look at

14 stars14 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

What its author says it does

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Reviews JUCE audio plugin code for JUCE-specific correctness issues: thread safety, APVTS parameter patterns, MessageManager usage, ValueTree, and MIDI handling. Use when the user asks to review a JUCE plugin, check a processBlock, audit parameter handling, or asks "is this JUCE code safe?". Trigger on phrases like "review my JUCE plugin", "check my AudioProcessor", "is this APVTS usage correct?", or when you see AudioProcessor, AudioProcessorEditor, or AudioProcessorValueTreeState in the code.

SKILL.md

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JUCE Audio Plugin Review

JUCE abstractions hide thread boundaries — always trace which thread each piece of code runs on before declaring it safe.

Step 0 — Run universal checks first

Invoke audio-dsp-review and audio-numerics-review before this skill. This skill adds JUCE-specific checks on top; it does not replace realtime-safety or numerics reviews.

Step 1 — Identify plugin structure

Locate the three core classes and their thread ownership:

AudioProcessor — audio thread owns processBlock; message thread owns everything else
AudioProcessorEditor — message thread only; never call from audio thread
AudioProcessorValueTreeState — parameter tree lives on message thread; audio thread must use getRawParameterValue() raw pointers only

Step 2 — Scan for JUCE violations

Violation	Where to look	Risk
`juce::String` construction/concatenation	`processBlock`, DSP helpers	May allocate and may touch shared string/logging machinery; realtime unsafe
`DBG()` macro	Any audio-thread code	Logger I/O in debug builds; blocks indefinitely
`MessageManager::getInstance()` from audio thread	Audio callbacks, DSP helpers	Not thread-safe; undefined behaviour
`apvts.getParameter(...)` or `apvts.state` from audio thread	`processBlock` and DSP helpers	APVTS/ValueTree access is not an audio-thread data path; use raw pointer cache instead
`ValueTree` listener callbacks assumed on audio thread	Listener overrides	Dispatched via MessageManager; runs on message thread
`AudioBuffer::setSize()` inside `processBlock`	Buffer management code	Triggers allocation; causes xrun
Modifying MIDI buffer while iterating it	MIDI event loops	Iterator invalidation; undefined behaviour
`prepareToPlay` not resetting all state (e.g. filters, envelopes, delay lines)	`prepareToPlay` body	Double-call leaves stale state; causes audio artefacts
`juce::CriticalSection::tryEnter()` or `enter()` on audio thread	`processBlock`, DSP helpers	`exit()`/destructor does a syscall to wake waiting threads — not realtime-safe even with `tryEnter()`
`juce::SpinLock::enter()` on audio thread	`processBlock`, DSP helpers	Busy-waits on audio thread — use `tryEnter()` + fallback only; non-audio thread should use progressive back-off

Step 3 — Write the review

## JUCE Plugin Review: `[file / class]`

### Verdict
[Safe | Has critical violations | Warnings only] — [one sentence summary]

### Critical Violations
**[Category]: [description]**
`file:line` — `offending code`
Why: [one sentence on thread / correctness risk]
Fix: [concrete JUCE-idiomatic suggestion]

### Warnings
[same format]

### What's Done Well
[correct patterns observed]

### Recommended Fixes (priority order)
1. ...

Quick fix table

Violation	Fix
`juce::String` in `processBlock`	Pre-format on message thread; pass IDs/scalars via `AbstractFifo` or atomics
`DBG()` in audio code	Remove entirely or gate behind a lock-free ring buffer drained on message thread
`MessageManager` from audio thread	Use `juce::MessageManager::callAsync` from message thread only
`apvts.getParameter(id)` in audio thread	Cache `getRawParameterValue(id)` once after APVTS construction; read atomically in `processBlock`
`ValueTree` listener on audio thread	Handle listener callbacks on message thread; pass state to audio thread via atomics
`AudioBuffer::setSize()` in `processBlock`	Call only in `prepareToPlay`; never resize during playback
Mutating MIDI buffer mid-iteration	Collect into a preallocated member buffer or bounded event array, then swap/write back after iteration
Missing state reset in `prepareToPlay`	Reset filters, envelopes, delay lines, and position counters unconditionally
`CriticalSection::tryEnter()` in audio thread	Replace with `std::atomic<T>` or lock-free SPSC queue; `tryEnter()` + `exit()` is not safe because `exit()` does a syscall
`SpinLock::enter()` on audio thread	Use `tryEnter()` + fallback only; non-audio thread should use progressive back-off (see `references/juce-violations.md` Section 4)

For full code examples (BAD/GOOD patterns, AbstractFifo usage, async dispatch) see references/juce-violations.md.