# Async Migration - Executive Summary

**Quick Overview:** Converting 150 generator functions to async/await across 28 progressive PRs

---

## The Plan in One Minute

### What?
Migrate ExaBGP from custom generator-based async to Python's native async/await

### Why?
- Modern Python patterns
- Better tooling support
- Easier maintenance
- Standard asyncio ecosystem

### How?
28 separate PRs across 5 phases, maintaining stability throughout

### When?
40-60 hours total work, split across multiple sessions

---

## Visual Roadmap

```
┌─────────────────────────────────────────────────────────────────┐
│ PHASE 1: INFRASTRUCTURE (3 PRs, 5-7 hours)                      │
│ ✓ Make ASYNC class support both generators & coroutines         │
└──────────────────────────┬──────────────────────────────────────┘
                           │
                           ▼
┌─────────────────────────────────────────────────────────────────┐
│ PHASE 2: CRITICAL PATH (5 PRs, 12-15 hours)                     │
│ ✓ Convert API handlers (30 generators)                          │
│ ✓ Convert Protocol handler (14 generators)                      │
│ ✓ Convert Peer state machine (9 generators)                     │
└──────┬────────────────────────────────────────────┬─────────────┘
       │                                            │
       ▼                                            ▼
┌──────────────────────────────┐    ┌──────────────────────────────┐
│ PHASE 3: SUPPORTING          │    │ PHASE 4: BGP PARSING         │
│ (10 PRs, 10-12 hours)        │    │ (5 PRs, 5-7 hours)           │
│ ✓ Connection handlers        │    │ ✓ UPDATE parser              │
│ ✓ RIB operations             │    │ ✓ Attribute parsers          │
│ ✓ Network layer              │    │ ✓ NLRI parsers               │
└──────────────────────────────┘    └──────────────────────────────┘
       │                                            │
       └────────────────┬───────────────────────────┘
                        ▼
┌─────────────────────────────────────────────────────────────────┐
│ PHASE 5: UTILITIES (5 PRs, 8-10 hours) [OPTIONAL]               │
│ ✓ Config parsers, CLI, Netlink, etc.                            │
└─────────────────────────────────────────────────────────────────┘
```

---

## Critical Success Factors

### 1. Infrastructure First
**Must complete PR #1-3 before anything else**
- PR #1: ASYNC class dual-mode support
- PR #2: Event loop async integration
- PR #3: Test utilities

### 2. Test Stability
**Never modify these test files - they validate our work:**
- `tests/unit/test_connection_advanced.py`
- `tests/fuzz/test_connection_reader.py`
- `tests/unit/test_route_refresh.py`

### 3. One PR at a Time
**Each PR is independent, tested, and mergeable**
- Clear scope
- Full test coverage
- Rollback plan included

### 4. Progressive Testing
**After each PR:**
- All tests must pass (100%)
- Coverage must not decrease
- Performance regression < 5%

---

## The Numbers

| Category | Count |
|----------|-------|
| **Total Files with Generators** | 44 |
| **Total Generator Functions** | ~150 |
| **Total PRs Planned** | 28 |
| **Total Phases** | 5 |
| **Critical Path PRs** | 8 (must complete) |
| **Optional PRs** | 5 (Phase 5) |
| **Test Files to Keep Stable** | 3 |

---

## Time Estimates

### By Phase
1. **Infrastructure:** 5-7 hours (3 PRs)
2. **Critical Path:** 12-15 hours (5 PRs)
3. **Supporting:** 10-12 hours (10 PRs)
4. **Parsing:** 5-7 hours (5 PRs)
5. **Utilities:** 8-10 hours (5 PRs, optional)

### Total
- **Minimum:** 40 hours (without Phase 5)
- **Maximum:** 60 hours (with Phase 5)
- **Sessions (2-4h each):** 10-30 sessions

---

## Top 5 Files to Convert

These represent 38% of all generators and drive core functionality:

1. **`reactor/api/command/announce.py`** - 30 generators
   - API command handlers
   - Highest priority
   - Split into 3 PRs

2. **`reactor/protocol.py`** - 14 generators
   - BGP message I/O
   - Critical path
   - 1 PR

3. **`reactor/peer.py`** - 9 generators
   - Peer state machine
   - Critical path
   - 1 PR

4. **`reactor/network/connection.py`** - 3 generators
   - TCP socket I/O
   - 1 PR

5. **`rib/outgoing.py`** - 2 generators
   - Route messages
   - 1 PR

**Total:** 58 generators (38% of all work)

---

## Phase Dependencies

```
Phase 1 (Infrastructure)
   │
   ├─► Phase 2 (Critical) ◄── Must complete before Phase 3/4
   │      │
   │      └─► Phase 3 (Supporting) ──┐
   │      └─► Phase 4 (Parsing) ─────┤
   │                                  │
   └─────────────────────────────────┴─► Phase 5 (Optional)
```

**Key Rule:** Complete Infrastructure → Critical Path → Rest can parallelize

---

## Risk Management

### High-Risk PRs (need extra care)
- **PR #2:** Event loop integration (core infrastructure)
- **PR #4-6:** API handlers (heavy usage)
- **PR #7:** Protocol handler (BGP I/O)
- **PR #8:** Peer state machine (complex state)

### Mitigation
- Extensive testing required
- Backward compatibility maintained
- Feature flags for rollback
- Session checkpoints for safety

### Rollback Strategy
Each PR includes:
- Compatible with both old and new code
- Can revert without breaking others
- ASYNC class supports dual-mode throughout

---

## Success Criteria

### Phase 1 Complete
✓ ASYNC class works with generators AND coroutines
✓ Event loop integrated with asyncio
✓ All existing tests still pass

### Phase 2 Complete
✓ 58 critical generators converted (38%)
✓ API, Protocol, and Peer fully async
✓ Core functionality stable

### Final Success
✓ 150 generators converted (or 102 if skipping Phase 5)
✓ 100% test pass rate maintained
✓ No performance regression
✓ Documentation complete

---

## Quick Start

### Right Now
1. Read: `ASYNC_MIGRATION_PLAN.md` (full details)
2. Read: `MIGRATION_QUICK_START.md` (how to start)
3. Run: Baseline tests
4. Start: PR #1 (Infrastructure)

### This Session
```bash
# Record baseline
PYTHONPATH=src python -m pytest tests/ -v --cov=src/exabgp > baseline.log

# Create PR branch
git checkout -b async-pr-01-infrastructure

# Modify asynchronous.py
# (see MIGRATION_QUICK_START.md for details)

# Test
PYTHONPATH=src python -m pytest tests/ -v

# Commit and push
git commit -m "[async-migration] PR #1: Add async/await infrastructure"
git push -u origin async-pr-01-infrastructure
```

---

## Documentation Index

All migration documents:

1. **`ASYNC_MIGRATION_PLAN.md`** ← Full detailed plan (28 PRs, all phases)
2. **`MIGRATION_QUICK_START.md`** ← How to start immediately
3. **`MIGRATION_PROGRESS.md`** ← Track progress across sessions
4. **`MIGRATION_SUMMARY.md`** ← This document (overview)
5. **`.github/PULL_REQUEST_TEMPLATE_ASYNC_MIGRATION.md`** ← PR template

Analysis documents (from exploration):
- `/tmp/generator_analysis.md` - Detailed analysis
- `/tmp/quick_reference.md` - Quick reference
- `/tmp/files_summary.txt` - File listing

---

## Key Principles

### 🎯 Progressive
One PR at a time, never break existing code

### 🧪 Test-Driven
Every change validated by stable test suite

### 🔄 Reversible
Each PR can rollback independently

### 📊 Measurable
Track generators converted, tests passing, coverage

### 📝 Documented
Clear plan, progress tracking, session handoffs

---

## Session Workflow

### Start of Session
1. Review `MIGRATION_PROGRESS.md`
2. Check last session's notes
3. Pull latest from main branch
4. Identify next PR to work on

### During Session
1. Create PR branch
2. Make changes (follow conversion patterns)
3. Write/update tests
4. Run full test suite
5. Commit with proper message

### End of Session
1. Update `MIGRATION_PROGRESS.md`
2. Push changes
3. Create PR (or mark work-in-progress)
4. Document handoff notes

---

## Questions?

- **Full details?** See `ASYNC_MIGRATION_PLAN.md`
- **How to start?** See `MIGRATION_QUICK_START.md`
- **Track progress?** See `MIGRATION_PROGRESS.md`
- **Conversion patterns?** See `ASYNC_MIGRATION_PLAN.md` Appendix B

---

## TL;DR - The Absolute Minimum

1. **Goal:** Convert 150 generators to async/await
2. **Method:** 28 PRs across 5 phases
3. **Time:** 40-60 hours total
4. **Start:** PR #1 - Update ASYNC class
5. **Critical:** Maintain test stability throughout
6. **Success:** All tests pass, no breaking changes

**Ready to begin?** → `MIGRATION_QUICK_START.md`
