Rename use_multiple_gpus to use_multi_process

Because this also supports multiple CPUs & multi_process is what the underlying code is called.
Also stop the pools afterwards again
And remove code duplication

sentence_transformers/util.py

@@ -535,8 +535,8 @@ def mine_hard_negatives(
     batch_size: int = 32,
     faiss_batch_size: int = 16384,
     use_faiss: bool = False,
+    use_multi_process: list[str] | bool = False,
     verbose: bool = True,
-    use_multiple_gpus=False,
 ) -> Dataset:
     """
     Add hard negatives to a dataset of (anchor, positive) pairs to create (anchor, positive, negative) triplets or
@@ -644,6 +644,9 @@ def mine_hard_negatives(
         batch_size (int): Batch size for encoding the dataset. Defaults to 32.
         faiss_batch_size (int): Batch size for FAISS top-k search. Defaults to 16384.
         use_faiss (bool): Whether to use FAISS for similarity search. May be recommended for large datasets. Defaults to False.
+        use_multi_process (bool | List[str], optional): Whether to use multi-GPU/CPU processing. If True, uses all GPUs if CUDA
+            is available, and 4 CPU processes if it's not available. You can also pass a list of PyTorch devices like
+            ["cuda:0", "cuda:1", ...] or ["cpu", "cpu", "cpu", "cpu"].
         verbose (bool): Whether to print statistics and logging. Defaults to True.
 
     Returns:
@@ -718,6 +721,30 @@ def mine_hard_negatives(
         avg_positives_per_query = np.mean(positives_per_query)
         print(f"Found an average of {avg_positives_per_query:.3f} positives per query.")
 
+    # Embed the corpus and the queries
+    if use_multi_process:
+        pool = model.start_multi_process_pool(
+            target_devices=None if isinstance(use_multi_process, bool) else use_multi_process
+        )
+        corpus_embeddings = model.encode_multi_process(
+            corpus, pool, batch_size=batch_size, normalize_embeddings=True, show_progress_bar=True
+        )
+        query_embeddings = model.encode_multi_process(
+            queries, pool, batch_size=batch_size, normalize_embeddings=True, show_progress_bar=True
+        )
+        model.stop_multi_process_pool(pool)
+    else:
+        corpus_embeddings = model.encode(
+            corpus, batch_size=batch_size, normalize_embeddings=True, convert_to_numpy=True, show_progress_bar=True
+        )
+        query_embeddings = model.encode(
+            queries,
+            batch_size=batch_size,
+            normalize_embeddings=True,
+            convert_to_numpy=True,
+            show_progress_bar=True,
+        )
+
     if use_faiss:
         import faiss
 
@@ -731,27 +758,6 @@ def mine_hard_negatives(
         except Exception:
             pass
 
-        if use_multiple_gpus:
-            pool = model.start_multi_process_pool()
-
-            corpus_embeddings = model.encode_multi_process(
-                corpus, pool, batch_size=batch_size, normalize_embeddings=True, show_progress_bar=True
-            )
-
-            query_embeddings = model.encode_multi_process(
-                queries, pool, batch_size=batch_size, normalize_embeddings=True, show_progress_bar=True
-            )
-        else:
-            corpus_embeddings = model.encode(
-                corpus, batch_size=batch_size, normalize_embeddings=True, convert_to_numpy=True, show_progress_bar=True
-            )
-            query_embeddings = model.encode(
-                queries,
-                batch_size=batch_size,
-                normalize_embeddings=True,
-                convert_to_numpy=True,
-                show_progress_bar=True,
-            )
         index.add(corpus_embeddings)
 
         scores_list = []
@@ -766,29 +772,7 @@ def mine_hard_negatives(
         indices = torch.from_numpy(np.concatenate(indices_list, axis=0)).to(device)
 
     else:
-        # Embed the corpus and the queries
-
-        if use_multiple_gpus:
-            pool = model.start_multi_process_pool()
-
-            corpus_embeddings = model.encode_multi_process(
-                corpus, pool, batch_size=batch_size, normalize_embeddings=True, show_progress_bar=True
-            )
-
-            query_embeddings = model.encode_multi_process(
-                queries, pool, batch_size=batch_size, normalize_embeddings=True, show_progress_bar=True
-            )
-        else:
-            corpus_embeddings = model.encode(
-                corpus, batch_size=batch_size, normalize_embeddings=True, convert_to_numpy=True, show_progress_bar=True
-            )
-            query_embeddings = model.encode(
-                queries,
-                batch_size=batch_size,
-                normalize_embeddings=True,
-                convert_to_numpy=True,
-                show_progress_bar=True,
-            )
+        # Compute the similarity scores between the queries and the corpus
         scores = model.similarity(query_embeddings, corpus_embeddings).to(device)
 
         # Keep only the range_max + max_positives highest scores. We offset by 1 to potentially include the positive pair