HostProcessor Thread Safety & Logic Review - Summary

HostProcessor Thread Safety & Logic Review - Summary

Files Modified

1. HostProcessor.kt - Complete refactor for thread safety and better connection logic
2. PeerSessionManager.kt - Added mutex for thread-safe session tracking
3. BeaconService.kt - Improved wire handling and added cleanup methods
4. NodeEmitProcessor.kt - Fixed LazyThreadSafetyMode
5. NodeEmitAppProcessor.kt - Fixed LazyThreadSafetyMode

Key Improvements

1. Thread Safety

• All dependency injection now uses LazyThreadSafetyMode.SYNCHRONIZED instead of NONE
• PeerSessionManager now has mutex protection for its session map
• Wire processing protected by wireProcessingMutex to prevent concurrent modifications
• BeaconService already had proper mutex protection - now enhanced with better error handling

2. Missing Connection Conditions Fixed

Scenario	Before	After
Server restart	Only re-handshaked if known peer	✅ Always re-handshakes + updates session
Client restart	Only advertised if I’m a server	✅ Always advertises + updates session
Duplicate beacon	Processed same as first	✅ Updates metadata only, no reconnect
New peer discovery	Correct	✅ No change needed
Multiple emit() calls	Could create duplicate listeners	✅ BeaconService deduplicates via jobs map

3. Connection Logic Flow (New)

Wire Received
    ↓
wireProcessingMutex.withLock
    ↓
Check if Server/Client type
    ↓
Read from NodeManager (check if known)
    ↓
Check session in PeerSessionManager (mutex protected)
    ↓
┌─────────────────────────────────────────┐
│ New Peer (NodeFlow.Error)              │
│ - Add session                            │
│ - Create node stub                       │
│ - If Server: trustServer()               │
│ - If Client: advertise back              │
└─────────────────────────────────────────┘
    OR
┌─────────────────────────────────────────┐
│ Known Peer + New Session                │
│ - Update session                         │
│ - Update node metadata                   │
│ - If Server: re-trustServer()            │
│   + advertise if I'm server too          │
│ - If Client: advertise                   │
└─────────────────────────────────────────┘
    OR
┌─────────────────────────────────────────┐
│ Known Peer + Same Session               │
│ - Update node metadata only              │
│ - No reconnection (prevent loops)        │
└─────────────────────────────────────────┘

4. Error Handling

• Try-catch blocks around all wire processing
• Errors logged with context (wire ID, type, error message)
• Service continues even if one wire processing fails
• BeaconService errors don’t crash the entire service

5. Deduplication Strategy

BeaconService Level (Singleton):

• Tracks active beacon listener jobs in jobs: MutableMap<String, Job>
• start(node) checks if jobs.containsKey(node.id) before creating listener
• Thread-safe with beaconJobMutex

Result: Multiple calls to HostProcessor.emit() are safe because BeaconService ensures only one listener per node.id

Testing Checklist

Unit Tests

• Multiple concurrent emit() calls
• Server restart (new session)
• Client restart (new session)
• New peer discovery
• Duplicate beacon (same session)
• Concurrent wire processing

Integration Tests

• Server crash and reconnect
• Multiple clients connecting simultaneously
• Network partition and recovery
• Heavy beacon traffic (stress test)

Manual Tests

1. Start server → start client → verify connection
2. Restart server → verify client reconnects
3. Restart client → verify server recognizes
4. Kill server, wait 30s, restart → verify full recovery
5. Start 10 clients simultaneously → verify all connect

Metrics to Monitor

1. Beacon listener count - Should be 1 per node.id (check BeaconService.jobs.size)
2. Session map size - Should equal number of unique peers
3. Wire processing errors - Should be rare (network issues only)
4. Reconnection latency - Time from server restart to client reconnect

Known Limitations

1. No session cleanup - Sessions accumulate forever in PeerSessionManager
   • Recommendation: Add TTL or explicit disconnect handling
2. No explicit shutdown integration - shutdown() exists but not called
   • Recommendation: Hook into application lifecycle
3. WebSocket lifecycle separate - Connection state not synchronized with sessions
   • Recommendation: Coordinate WebSocket cleanup with session removal

Performance Impact

• Minimal overhead from mutex locking (only during wire processing, not data flow)
• No blocking - all operations are suspend functions
• BeaconService deduplication prevents resource waste from duplicate listeners

Migration Notes

No breaking API changes - all changes are internal to the processor implementations.

Existing code will benefit from thread safety improvements without modification.

Build Status

✅ All platforms compile successfully ✅ No new errors introduced ⚠️ Only harmless warnings (unused parameters, unused methods)