# NX Session Management

**Status**: Implemented
**Version**: 1.0
**Date**: 2025-11-20

## Problem

When running multiple optimizations concurrently or when a user has NX open for manual work, conflicts can occur:

1. **Multiple Optimizations**: Two optimization studies trying to modify the same model simultaneously
2. **User's Interactive NX**: Batch optimization interfering with user's manual work
3. **File Corruption**: Concurrent writes to .prt/.sim files causing corruption
4. **License Conflicts**: Multiple NX instances competing for licenses
5. **Journal Failures**: Journals trying to run on wrong NX session

## Solution: NX Session Manager

The `NXSessionManager` class provides intelligent session conflict prevention.

### Key Features

1. **Session Detection**
   - Detects all running NX processes (interactive + batch)
   - Identifies interactive vs batch sessions
   - Warns if user has NX open

2. **File Locking**
   - Exclusive locks on model files (.prt)
   - Prevents two optimizations from modifying same model
   - Queues trials if model is locked

3. **Process Queuing**
   - Limits concurrent NX batch sessions (default: 1)
   - Waits if max sessions reached
   - Automatic timeout and error handling

4. **Stale Lock Cleanup**
   - Detects crashed processes
   - Removes orphaned lock files
   - Prevents permanent deadlocks

## Architecture

### Session Manager Components

```python
from optimization_engine.nx_session_manager import NXSessionManager

# Initialize
session_mgr = NXSessionManager(
    lock_dir=Path.home() / ".atomizer" / "locks",
    max_concurrent_sessions=1,  # Max parallel NX instances
    wait_timeout=300,            # Max wait time (5 min)
    verbose=True
)
```

### Two-Level Locking

**Level 1: Model File Lock** (most important)
```python
# Ensures exclusive access to a specific model
with session_mgr.acquire_model_lock(prt_file, study_name):
    # Update CAD model
    updater.update_expressions(params)

    # Run simulation
    result = solver.run_simulation(sim_file)
```

**Level 2: NX Session Lock** (optional)
```python
# Limits total concurrent NX batch instances
with session_mgr.acquire_nx_session(study_name):
    # Run NX batch operation
    pass
```

## Usage Examples

### Example 1: Single Optimization (Recommended)

```python
from optimization_engine.nx_solver import NXSolver
from optimization_engine.nx_updater import NXParameterUpdater
from optimization_engine.nx_session_manager import NXSessionManager

# Initialize components
session_mgr = NXSessionManager(verbose=True)
updater = NXParameterUpdater("model.prt")
solver = NXSolver()

# Check for interactive NX sessions
if session_mgr.is_nx_interactive_session_running():
    print("WARNING: NX is open! Close it before running optimization.")
    # You can choose to abort or continue

# Run trials with session management
for trial in trials:
    with session_mgr.acquire_model_lock(prt_file, "my_study"):
        # Exclusive access to model - safe to modify
        updater.update_expressions(params)
        result = solver.run_simulation(sim_file)
```

### Example 2: Multiple Concurrent Optimizations

```python
# Study A (in one terminal)
session_mgr_A = NXSessionManager()

with session_mgr_A.acquire_model_lock(model_A_prt, "study_A"):
    # Works on model A
    updater_A.update_expressions(params_A)
    solver_A.run_simulation(sim_A)

# Study B (in another terminal, simultaneously)
session_mgr_B = NXSessionManager()

with session_mgr_B.acquire_model_lock(model_B_prt, "study_B"):
    # Works on model B (different model - no conflict)
    updater_B.update_expressions(params_B)
    solver_B.run_simulation(sim_B)

# If they try to use SAME model:
with session_mgr_A.acquire_model_lock(model_SAME, "study_A"):
    pass  # Acquires lock

with session_mgr_B.acquire_model_lock(model_SAME, "study_B"):
    # Waits here until study_A releases lock
    # Then proceeds safely
    pass
```

### Example 3: Protection Against User's Interactive NX

```python
session_mgr = NXSessionManager(verbose=True)

# Detect if user has NX open
nx_sessions = session_mgr.get_running_nx_sessions()

for session in nx_sessions:
    print(f"Detected: {session.name} (PID {session.pid})")

if session_mgr.is_nx_interactive_session_running():
    print("Interactive NX session detected!")
    print("Recommend closing NX before running optimization.")

    # Option 1: Abort
    raise RuntimeError("Close NX and try again")

    # Option 2: Continue with warning
    print("Continuing anyway... (may cause conflicts)")
```

## Configuration

### Lock Directory

Default: `~/.atomizer/locks/`

Custom:
```python
session_mgr = NXSessionManager(
    lock_dir=Path("/custom/lock/dir")
)
```

### Concurrent Session Limit

Default: 1 (safest)

Allow multiple:
```python
session_mgr = NXSessionManager(
    max_concurrent_sessions=2  # Allow 2 parallel NX batches
)
```

**Warning**: Multiple concurrent NX sessions require multiple licenses!

### Wait Timeout

Default: 300 seconds (5 minutes)

Custom:
```python
session_mgr = NXSessionManager(
    wait_timeout=600  # Wait up to 10 minutes
)
```

## Integration with NXSolver

The `NXSolver` class has built-in session management:

```python
from optimization_engine.nx_solver import NXSolver

solver = NXSolver(
    enable_session_management=True,  # Default
    study_name="my_study"
)

# Session management happens automatically
result = solver.run_simulation(sim_file)
```

**Note**: Full automatic integration is planned but not yet implemented. Currently, manual wrapping is recommended.

## Status Monitoring

### Get Current Status

```python
report = session_mgr.get_status_report()
print(report)
```

Output:
```
======================================================================
  NX SESSION MANAGER STATUS
======================================================================

  Running NX Processes: 2
    PID 12345: ugraf.exe
      Working dir: C:/Users/username/project
    PID 12346: run_journal.exe

  WARNING: Interactive NX session detected!
           Batch operations may conflict with user's work.

  Active Optimization Sessions: 1/1
    my_study (PID 12347)

  Active Lock Files: 1
======================================================================
```

### Cleanup Stale Locks

```python
# Run at startup
session_mgr.cleanup_stale_locks()
```

Removes lock files from crashed processes.

## Error Handling

### Lock Timeout

```python
try:
    with session_mgr.acquire_model_lock(prt_file, study_name):
        # ... modify model ...
        pass
except TimeoutError as e:
    print(f"Could not acquire model lock: {e}")
    print("Another optimization may be using this model.")
    # Handle error (skip trial, abort, etc.)
```

### NX Session Timeout

```python
try:
    with session_mgr.acquire_nx_session(study_name):
        # ... run NX batch ...
        pass
except TimeoutError as e:
    print(f"Could not acquire NX session: {e}")
    print(f"Max concurrent sessions ({session_mgr.max_concurrent}) reached.")
    # Handle error
```

## Platform Support

- ✅ **Windows**: Full support (uses `msvcrt` for file locking)
- ✅ **Linux/Mac**: Full support (uses `fcntl` for file locking)
- ✅ **Cross-Platform**: Lock files work across different OS instances

## Limitations

1. **Same Machine Only**: Session manager only prevents conflicts on the same machine
   - For networked optimizations, need distributed lock manager

2. **File System Required**: Requires writable lock directory
   - May not work on read-only filesystems

3. **Process Detection**: Relies on `psutil` for process detection
   - May miss processes in some edge cases

4. **Not Real-Time**: Lock checking has small latency
   - Not suitable for microsecond-level synchronization

## Best Practices

### 1. Always Use Model Locks

```python
# GOOD: Protected
with session_mgr.acquire_model_lock(prt_file, study_name):
    updater.update_expressions(params)

# BAD: Unprotected (race condition!)
updater.update_expressions(params)
```

### 2. Check for Interactive NX

```python
# Before starting optimization
if session_mgr.is_nx_interactive_session_running():
    print("WARNING: Close NX before running optimization!")
    # Decide: abort or continue with warning
```

### 3. Cleanup on Startup

```python
# At optimization start
session_mgr = NXSessionManager()
session_mgr.cleanup_stale_locks()  # Remove crashed process locks
```

### 4. Use Unique Study Names

```python
# GOOD: Unique names
solver_A = NXSolver(study_name="beam_optimization_trial_42")
solver_B = NXSolver(study_name="plate_optimization_trial_15")

# BAD: Same name (confusing logs)
solver_A = NXSolver(study_name="default_study")
solver_B = NXSolver(study_name="default_study")
```

### 5. Handle Timeouts Gracefully

```python
try:
    with session_mgr.acquire_model_lock(prt_file, study_name):
        result = solver.run_simulation(sim_file)
except TimeoutError:
    # Don't crash entire optimization!
    print("Lock timeout - skipping this trial")
    raise optuna.TrialPruned()  # Optuna will continue
```

## Troubleshooting

### "Lock timeout" errors

**Cause**: Another process holds the lock longer than timeout

**Solutions**:
1. Check if another optimization is running
2. Increase timeout: `wait_timeout=600`
3. Check for stale locks: `cleanup_stale_locks()`

### "Interactive NX session detected" warnings

**Cause**: User has NX open in GUI mode

**Solutions**:
1. Close interactive NX before optimization
2. Use different model files
3. Continue with warning (risky!)

### Stale lock files

**Cause**: Optimization crashed without releasing locks

**Solution**:
```python
session_mgr.cleanup_stale_locks()
```

### Multiple optimizations on different models still conflict

**Cause**: NX session limit reached

**Solution**:
```python
session_mgr = NXSessionManager(
    max_concurrent_sessions=2  # Allow 2 parallel NX instances
)
```

**Warning**: Requires 2 NX licenses!

## Future Enhancements

- [ ] Distributed lock manager (for cluster computing)
- [ ] Automatic NX session affinity (assign trials to specific NX instances)
- [ ] License pool management
- [ ] Network file lock support (for shared drives)
- [ ] Real-time session monitoring dashboard
- [ ] Automatic crash recovery

## Version History

### Version 1.0 (2025-11-20)
- Initial implementation
- Model file locking
- NX session detection
- Concurrent session limiting
- Stale lock cleanup
- Status reporting

---

**Implementation Status**: ✅ Core functionality complete
**Testing Status**: ⚠️ Needs production testing
**Documentation Status**: ✅ Complete