Pytorch Problem: My jupyter stuck when num_workers > 0

This is a snippet of my code in PyTorch, my jupiter notebook stuck when I used num_workers > 0, I spent a lot on this problem without any answer. I do not have a GPU and I work only with a CPU.

class IndexedDataset(Dataset):

def __init__(self,data,targets, test=False):
    self.dataset = data 
    if not test:
        self.labels = targets.numpy()
        self.mask =  np.concatenate((np.zeros(NUM_LABELED), np.ones(NUM_UNLABELED)))


    def __len__(self):
        return len(self.dataset)

    def __getitem__(self, idx):
        image = self.dataset[idx]
        return image, self.labels[idx]
    
    def display(self, idx):
        plt.imshow(self.dataset[idx], cmap='gray')
        plt.show()

train_set = IndexedDataset(train_data, train_target, test = False)

test_set = IndexedDataset(test_data, test_target, test = True)

train_loader = DataLoader(train_set, batch_size=BATCH_SIZE, num_workers=2)

test_loader = DataLoader(test_set, batch_size=BATCH_SIZE, num_workers=2)

Any help, appreciated.

When num_workers is greater than 0, PyTorch uses multiple processes for data loading.

Jupyter notebooks have known issues with multiprocessing.

One way to resolve this is not to use Jupyter notebooks - just write a normal .py file and run it via command-line.

Or try use what's suggested here: Jupyter notebook never finishes processing using multiprocessing (Python 3).