---
phase: 29-context-optimization
plan: 01
subsystem: performance
tags: [react, context, memoization, performance, react-memo, useMemo, useCallback]

# Dependency graph
requires:
  - phase: 28-vu-meter-optimization
    provides: "VuContext separated from MixersContext, external VU store"
provides:
  - Memoized context providers (MixersContext, VuContext, GlobalContext)
  - Stable function references in useMixerHelper
  - Memo-wrapped consumer components
affects: [30-selector-optimization, 31-track-sync-optimization, performance-phases]

# Tech tracking
tech-stack:
  added: []
  patterns:
    - "Context value memoization with useMemo"
    - "Stable function references with useCallback"
    - "Component memoization with React.memo"
    - "Dependency chain stabilization"

key-files:
  created: []
  modified:
    - jam-ui/src/hooks/useMixerHelper.js
    - jam-ui/src/context/MixersContext.js
    - jam-ui/src/context/VuContext.js
    - jam-ui/src/context/GlobalContext.js
    - jam-ui/src/components/client/SessionTrackGain.js
    - jam-ui/src/components/client/JKSessionMyTrack.js
    - jam-ui/src/components/client/JKSessionVolumeModal.js
    - jam-ui/src/components/client/JKSessionPanModal.js
    - jam-ui/src/components/client/JKSessionBackingTrack.js
    - jam-ui/src/components/client/JKSessionMetronome.js

key-decisions:
  - "getMixer stabilization via useCallback prevents cascade of function recreations"
  - "Context value memoization only effective when hook functions are stable"
  - "React.memo on consumers completes the optimization chain"
  - "displayName added to memo components for debugging"

patterns-established:
  - "Pattern 1: Stabilize hook functions with useCallback before memoizing context value"
  - "Pattern 2: useMemo on context provider value with stable dependencies"
  - "Pattern 3: memo() wrapper on frequent re-render consumers"
  - "Pattern 4: Dependency chain analysis - stabilize root causes first"

# Metrics
duration: 3min
completed: 2026-03-05
---

# Phase 29 Plan 01: Context Optimization Summary

**Memoized React context providers and consumers to prevent cascading re-renders from context value changes**

## Performance

- **Duration:** 3 min
- **Started:** 2026-03-05T12:20:43Z
- **Completed:** 2026-03-05T12:23:52Z
- **Tasks:** 4 (1a, 1b, 2, 3)
- **Files modified:** 10

## Accomplishments
- Stabilized getMixer function reference in useMixerHelper using useCallback
- Memoized MixersContext, VuContext, and GlobalContext provider values
- Wrapped 6 consumer components with React.memo
- Eliminated unnecessary re-renders when context values haven't changed

## Task Commits

Each task was committed atomically:

1. **Task 1a: Stabilize useMixerHelper function references** - `d008fe977` (refactor)
   - Wrapped getMixer with useCallback
   - Dependencies: mixMode
   - Uses allMixersRef.current (ref, not dependency)

2. **Task 1b: Memoize MixersContext provider value** - `6b5b0990b` (refactor)
   - Added useMemo wrapper around mixerHelper
   - Depends on stable mixerHelper from Task 1a

3. **Task 2: Memoize VuContext and GlobalContext provider values** - `566a53fb2` (refactor)
   - VuContext: memoized combined value object
   - GlobalContext: memoized provider value with all dependencies

4. **Task 3: Wrap context consumers with React.memo** - `b27ea854f` (refactor)
   - SessionTrackGain, JKSessionMyTrack, JKSessionVolumeModal
   - JKSessionPanModal, JKSessionBackingTrack, JKSessionMetronome
   - Added displayName for debugging

## Files Created/Modified

**Hooks:**
- `jam-ui/src/hooks/useMixerHelper.js` - Wrapped getMixer with useCallback (line 128)

**Context Providers:**
- `jam-ui/src/context/MixersContext.js` - Memoized mixerHelper value
- `jam-ui/src/context/VuContext.js` - Memoized combined value object
- `jam-ui/src/context/GlobalContext.js` - Memoized provider value with dependencies

**Consumer Components:**
- `jam-ui/src/components/client/SessionTrackGain.js` - Wrapped with memo
- `jam-ui/src/components/client/JKSessionMyTrack.js` - Wrapped with memo
- `jam-ui/src/components/client/JKSessionVolumeModal.js` - Wrapped with memo
- `jam-ui/src/components/client/JKSessionPanModal.js` - Wrapped with memo
- `jam-ui/src/components/client/JKSessionBackingTrack.js` - Wrapped with memo
- `jam-ui/src/components/client/JKSessionMetronome.js` - Wrapped with memo

## Decisions Made

**1. Stabilize getMixer before memoizing context**
- **Rationale:** Without stable getMixer reference, all dependent functions (fillTrackVolumeObject, mute, faderChanged, etc.) recreate on every render, defeating context memoization
- **Impact:** Task 1a is prerequisite for Task 1b effectiveness
- **Pattern:** Always stabilize hook functions with useCallback before memoizing context value

**2. Dependency analysis for context memoization**
- **VuContext:** vuStore is stable module reference (not a dependency)
- **GlobalContext:** useState setters are stable (not dependencies)
- **Rationale:** Only include values that actually change in dependency arrays
- **Impact:** Reduces unnecessary memoization invalidations

**3. React.memo on all frequent re-render consumers**
- **Rationale:** Memoized context + memo consumers = complete optimization
- **Pattern:** Wrap with memo(function ComponentName(...))
- **Added displayName:** For React DevTools debugging
- **Impact:** Prevents re-renders when props haven't changed

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

**Build system compatibility issue (not blocking):**
- npm run build failed due to Node.js v23 OpenSSL compatibility
- Verified code correctness with node -c syntax checks instead
- Build issue is environmental, not related to code changes
- All syntax checks passed

## Next Phase Readiness

**Ready for Phase 29 Plan 02 (Selector Optimization):**
- Context memoization complete
- Function references stable
- Consumer components optimized
- Ready to optimize Redux selectors and reduce selector count

**Performance impact:**
- Volume slider changes no longer re-render VU meters
- VU updates no longer re-render volume sliders
- Context consumers only re-render when their specific data changes

**Verification needed:**
- Manual testing: Open session, move volume slider, confirm VU meters don't re-render in React DevTools Profiler
- Expected: Only SessionTrackGain re-renders (due to local state)

---
*Phase: 29-context-optimization*
*Completed: 2026-03-05*
