What is multiprocessing and when to use it?

Question

Accepted Answer

**multiprocessing** runs code in **separate processes**, bypassing the GIL.

```python
from multiprocessing import Process, Pool, Queue

# Process — manual management
def worker(n):
    return n * n

p = Process(target=worker, args=(5,))
p.start()
p.join()

# Pool — managed process pool
with Pool(4) as pool:
    results = pool.map(worker, range(10))
    print(results)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# Parallel map
results = pool.map(cpu_intensive, large_dataset)

# Async map
async_result = pool.map_async(worker, range(10))
print(async_result.get())
```

**Communication between processes:**
```python
from multiprocessing import Queue

q = Queue()
q.put(data)       # Send
data = q.get()    # Receive
```

**When to use:**
- CPU-intensive computations.
- Parallel data processing.
- Tasks that need true parallelism.

Python: What is multiprocessing and when to use it?