# Fixed JobQueue Implementation

Here's the corrected implementation with proper thread-safe locking:

```python
import threading

class JobQueue:
    def __init__(self):
        self.jobs = {}
        self.results = {}
        self.lock = threading.Lock()

    def add_job(self, job_id, data):
        with self.lock:
            self.jobs[job_id] = data
        return job_id

    def process_job(self, job_id, processor):
        with self.lock:
            if job_id not in self.jobs:
                return False

            # Claim the job by removing it from jobs dict
            data = self.jobs[job_id]
            del self.jobs[job_id]
        
        # Process outside the lock to avoid blocking other operations
        result = processor(data)
        
        with self.lock:
            self.results[job_id] = result
            
        return True

    def get_result(self, job_id):
        with self.lock:
            return self.results.get(job_id)
```

## Key Fixes Made:

1. **Added a lock** (`self.lock = threading.Lock()`) in `__init__` to protect shared state.

2. **Protected all dictionary access** with `with self.lock:` context manager to ensure atomic operations.

3. **Claimed jobs atomically** - The job is removed from `jobs` while holding the lock, preventing other threads from processing the same job.

4. **Released lock during processing** - Processing happens outside the lock to avoid blocking other threads from adding or checking jobs.

5. **Protected result storage** - The result is stored atomically with the lock held.

## Why This Fixes the Race Condition:

**Before the fix:**
- Thread A checks if job exists ✓
- Thread B checks if job exists ✓
- Thread A reads data and processes
- Thread B reads data and processes ← **Duplicate processing!**
- Both write results simultaneously ← **Race condition!**

**After the fix:**
- Thread A acquires lock, checks and removes job, releases lock
- Thread B acquires lock, job already removed, returns False
- Only one thread processes the job
- Results are written atomically

This ensures that each job is processed exactly once, even in a multi-threaded environment.