Importing `CLIPVisionModelWithProjection` crashes with `AttributeError: 'NoneType' object has no attribute 'dumps'`
Author: gml16
Pull request: no

### System Info

- `transformers` version: 4.39.3
- Platform: Linux-5.4.56.bsk.10-amd64-x86_64-with-glibc2.28
- Python version: 3.12.2
- Huggingface_hub version: 0.22.2
- Safetensors version: 0.4.3
- Accelerate version: not installed
- Accelerate config: not found
- PyTorch version (GPU?): 2.2.2+cpu (False)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: Yes

### Who can help?

@amyeroberts

### Information

- [ ] The official example scripts
- [X] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [X] My own task or dataset (give details below)

### Reproduction

Hi, here's a minimal reproduction of the issue,
File `a.py`:
```python
from b import BufferPool
from transformers import CLIPVisionModelWithProjection # if you comment this line out, it all works with no error
buffer_pool = BufferPool()
```

File `b.py`:
```python
from multiprocessing.pool import ThreadPool
class BufferPool:
    def __init__(self):
        self.producer_pool = ThreadPool()
```

When I run `python3 -m a`, I get the following traceback:
```
Exception ignored in: <function Pool.__del__ at 0x7f6bb5a81ee0>
Traceback (most recent call last):
  File "/home/guy.leroy/miniconda3/lib/python3.12/multiprocessing/pool.py", line 271, in __del__
  File "/home/guy.leroy/miniconda3/lib/python3.12/multiprocessing/queues.py", line 393, in put
AttributeError: 'NoneType' object has no attribute 'dumps'
```

Please note that the code runs without any error if I either run not as a module (without the `-m`) or if I comment out the unused import `from transformers import CLIPVisionModelWithProjection `.


### Expected behavior

Script runs should run fine, and produce no error or output.

Comments:
Hi @gml16, thanks for raising this issue and providing simple reproducers and the environment info - it really helps us! 

Tbh, I'm not super familiar with multiprocessing so don't have an immediate answer to what's happening here.

Playing with the examples provided, I tested a few things: 

* This is true for importing all HF models - not just CLIP i.e. running with `from transformers import BertModel` causes the same error
* This doesn't happen if just dummy models are imported i.e. torch and tensorflow aren't installed in the environment
* If only tensorflow is in the environment, then it will fail when importing TF models e.g. `TFBertModel` but other objects like `debug_utils` can be imported (these fail with torch in the env)  

Looking for the error online, it seems like this is caused by the pool not being closed properly. Modifying the files as shown below, I was above to resolve: 

a.py
```py
from b import BufferPool
from transformers import CLIPVisionModelWithProjection # if you comment this line out, it all works with no error

buffer_pool = BufferPool()
buffer_pool.close()
```

b.py
```py
from multiprocessing.pool import ThreadPool

class BufferPool:
    def __init__(self):
        self.producer_pool = ThreadPool()

    def close(self):
        self.producer_pool.close()
        self.producer_pool.join()
```

Why these imports are triggering this, I really don't know 

Hi @amyeroberts, thanks a lot for taking a look. This does solve my issue. I'll let you choose whether you want to close this issue. Thanks again for your help.

I'll close, and if anyone has any follow up or it doesn't fully solve it, then we can reopen :)