Allow user-managed Pool in Wav2Vec2ProcessorWithLM.batch_decode (#18351)

* [Wav2Vec2] Allow user-managed Pool in Wav2Vec2ProcessorWithLM.batch_decode

* [Wav2Vec2] Add user-managed LM's pool tests and usage examples

* Improve styling

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* [Wav2Vec2] Fix hyperlink references

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/source/en/model_doc/wav2vec2.mdx

@@ -73,6 +73,61 @@ This model was contributed by [patrickvonplaten](https://huggingface.co/patrickv
     - batch_decode
     - decode
 
+### Decoding multiple audios
+
+If you are planning to decode multiple batches of audios, you should consider using [`~Wav2Vec2ProcessorWithLM.batch_decode`] and passing an instantiated `multiprocessing.Pool`.
+Otherwise, [`~Wav2Vec2ProcessorWithLM.batch_decode`] performance will be slower than calling [`~Wav2Vec2ProcessorWithLM.decode`] for each audio individually, as it internally instantiates a new `Pool` for every call. See the example below:
+
+```python
+>>> # Let's see how to use a user-managed pool for batch decoding multiple audios
+>>> from multiprocessing import get_context
+>>> from transformers import AutoTokenizer, AutoProcessor, AutoModelForCTC
+>>> from datasets import load_dataset
+>>> import datasets
+>>> import torch
+
+>>> # import model, feature extractor, tokenizer
+>>> model = AutoModelForCTC.from_pretrained("patrickvonplaten/wav2vec2-base-100h-with-lm").to("cuda")
+>>> processor = AutoProcessor.from_pretrained("patrickvonplaten/wav2vec2-base-100h-with-lm")
+
+>>> # load example dataset
+>>> dataset = load_dataset("hf-internal-testing/librispeech_asr_dummy", "clean", split="validation")
+>>> dataset = dataset.cast_column("audio", datasets.Audio(sampling_rate=16_000))
+
+
+>>> def map_to_array(batch):
+...     batch["speech"] = batch["audio"]["array"]
+...     return batch
+
+
+>>> # prepare speech data for batch inference
+>>> dataset = dataset.map(map_to_array, remove_columns=["audio"])
+
+
+>>> def map_to_pred(batch, pool):
+...     inputs = processor(batch["speech"], sampling_rate=16_000, padding=True, return_tensors="pt")
+...     inputs = {k: v.to("cuda") for k, v in inputs.items()}
+
+...     with torch.no_grad():
+...         logits = model(**inputs).logits
+
+...     transcription = processor.batch_decode(logits.cpu().numpy(), pool).text
+...     batch["transcription"] = transcription
+...     return batch
+
+
+>>> # note: pool should be instantiated *after* `Wav2Vec2ProcessorWithLM`.
+>>> #       otherwise, the LM won't be available to the pool's sub-processes
+>>> # select number of processes and batch_size based on number of CPU cores available and on dataset size
+>>> with get_context("fork").Pool(processes=2) as pool:
+...     result = dataset.map(
+...         map_to_pred, batched=True, batch_size=2, fn_kwargs={"pool": pool}, remove_columns=["speech"]
+...     )
+
+>>> result["transcription"][:2]
+['MISTER QUILTER IS THE APOSTLE OF THE MIDDLE CLASSES AND WE ARE GLAD TO WELCOME HIS GOSPEL', "NOR IS MISTER COULTER'S MANNER LESS INTERESTING THAN HIS MATTER"]
+```
+
 ## Wav2Vec2 specific outputs
 
 [[autodoc]] models.wav2vec2_with_lm.processing_wav2vec2_with_lm.Wav2Vec2DecoderWithLMOutput

setup.py

@@ -164,7 +164,7 @@ _deps = [
     "tokenizers>=0.11.1,!=0.11.3,<0.14",
     "torch>=1.7,!=1.12.0",
     "torchaudio",
-    "pyctcdecode>=0.3.0",
+    "pyctcdecode>=0.4.0",
     "tqdm>=4.27",
     "unidic>=1.0.2",
     "unidic_lite>=1.0.7",

src/transformers/dependency_versions_table.py

@@ -70,7 +70,7 @@ deps = {
     "tokenizers": "tokenizers>=0.11.1,!=0.11.3,<0.14",
     "torch": "torch>=1.7,!=1.12.0",
     "torchaudio": "torchaudio",
-    "pyctcdecode": "pyctcdecode>=0.3.0",
+    "pyctcdecode": "pyctcdecode>=0.4.0",
     "tqdm": "tqdm>=4.27",
     "unidic": "unidic>=1.0.2",
     "unidic_lite": "unidic_lite>=1.0.7",

src/transformers/models/wav2vec2/tokenization_wav2vec2.py

@@ -442,9 +442,9 @@ class Wav2Vec2CTCTokenizer(PreTrainedTokenizer):
 
                 <Tip>
 
-                Please take a look at the Example of [`~models.wav2vec2.tokenization_wav2vec2.decode`] to better
+                Please take a look at the Example of [`~Wav2Vec2CTCTokenizer.decode`] to better understand how to make
-                understand how to make use of `output_word_offsets`.
+                use of `output_char_offsets`. [`~Wav2Vec2CTCTokenizer.batch_decode`] works the same way with batched
-                [`~model.wav2vec2.tokenization_wav2vec2.batch_decode`] works the same way with batched output.
+                output.
 
                 </Tip>
 
@@ -454,9 +454,9 @@ class Wav2Vec2CTCTokenizer(PreTrainedTokenizer):
 
                 <Tip>
 
-                Please take a look at the Example of [`~models.wav2vec2.tokenization_wav2vec2.decode`] to better
+                Please take a look at the Example of [`~Wav2Vec2CTCTokenizer.decode`] to better understand how to make
-                understand how to make use of `output_word_offsets`.
+                use of `output_word_offsets`. [`~Wav2Vec2CTCTokenizer.batch_decode`] works the same way with batched
-                [`~model.wav2vec2.tokenization_wav2vec2.batch_decode`] works the same way with batched output.
+                output.
 
                 </Tip>
 
@@ -515,8 +515,7 @@ class Wav2Vec2CTCTokenizer(PreTrainedTokenizer):
 
                 <Tip>
 
-                Please take a look at the example of [`~models.wav2vec2.tokenization_wav2vec2.decode`] to better
+                Please take a look at the example below to better understand how to make use of `output_char_offsets`.
-                understand how to make use of `output_word_offsets`.
 
                 </Tip>
 
@@ -526,8 +525,7 @@ class Wav2Vec2CTCTokenizer(PreTrainedTokenizer):
 
                 <Tip>
 
-                Please take a look at the example of [`~models.wav2vec2.tokenization_wav2vec2.decode`] to better
+                Please take a look at the example below to better understand how to make use of `output_word_offsets`.
-                understand how to make use of `output_word_offsets`.
 
                 </Tip>
 

src/transformers/models/wav2vec2_with_lm/processing_wav2vec2_with_lm.py

@@ -17,15 +17,18 @@ Speech processor class for Wav2Vec2
 """
 import os
 import warnings
-from contextlib import contextmanager
+from contextlib import contextmanager, nullcontext
 from dataclasses import dataclass
-from multiprocessing import get_context
+from multiprocessing import Pool, get_context, get_start_method
 from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Union
 
 import numpy as np
 
 from ...processing_utils import ProcessorMixin
-from ...utils import ModelOutput, requires_backends
+from ...utils import ModelOutput, logging, requires_backends
+
+
+logger = logging.get_logger(__name__)
 
 
 if TYPE_CHECKING:
@@ -115,7 +118,7 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
 
         This class method is simply calling Wav2Vec2FeatureExtractor's
         [`~feature_extraction_utils.FeatureExtractionMixin.from_pretrained`], Wav2Vec2CTCTokenizer's
-        [`~tokenization_utils_base.PreTrainedTokenizer.from_pretrained`], and
+        [`~tokenization_utils_base.PreTrainedTokenizerBase.from_pretrained`], and
         [`pyctcdecode.BeamSearchDecoderCTC.load_from_hf_hub`].
 
         Please refer to the docstrings of the methods above for more information.
@@ -280,6 +283,7 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
     def batch_decode(
         self,
         logits: np.ndarray,
+        pool: Optional[Pool] = None,
         num_processes: Optional[int] = None,
         beam_width: Optional[int] = None,
         beam_prune_logp: Optional[float] = None,
@@ -297,16 +301,32 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
 
         <Tip>
 
-        This function makes use of Python's multiprocessing.
+        This function makes use of Python's multiprocessing. Currently, multiprocessing is available only on Unix
+        systems (see this [issue](https://github.com/kensho-technologies/pyctcdecode/issues/65)).
+
+        If you are decoding multiple batches, consider creating a `Pool` and passing it to `batch_decode`. Otherwise,
+        `batch_decode` will be very slow since it will create a fresh `Pool` for each call. See usage example below.
 
         </Tip>
 
         Args:
             logits (`np.ndarray`):
                 The logits output vector of the model representing the log probabilities for each token.
+            pool (`multiprocessing.Pool`, *optional*):
+                An optional user-managed pool. If not set, one will be automatically created and closed. The pool
+                should be instantiated *after* `Wav2Vec2ProcessorWithLM`. Otherwise, the LM won't be available to the
+                pool's sub-processes.
+
+                <Tip>
+
+                Currently, only pools created with a 'fork' context can be used. If a 'spawn' pool is passed, it will
+                be ignored and sequential decoding will be used instead.
+
+                </Tip>
+
             num_processes (`int`, *optional*):
-                Number of processes on which the function should be parallelized over. Defaults to the number of
+                If `pool` is not set, number of processes on which the function should be parallelized over. Defaults
-                available CPUs.
+                to the number of available CPUs.
             beam_width (`int`, *optional*):
                 Maximum number of beams at each step in decoding. Defaults to pyctcdecode's DEFAULT_BEAM_WIDTH.
             beam_prune_logp (`int`, *optional*):
@@ -332,17 +352,19 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
 
                 <Tip>
 
-                Please take a look at the Example of [`~model.wav2vec2_with_lm.processing_wav2vec2_with_lm.decode`] to
+                Please take a look at the Example of [`~Wav2Vec2ProcessorWithLM.decode`] to better understand how to
-                better understand how to make use of `output_word_offsets`.
+                make use of `output_word_offsets`. [`~Wav2Vec2ProcessorWithLM.batch_decode`] works the same way with
-                [`~model.wav2vec2_with_lm.processing_wav2vec2_with_lm.batch_decode`] works the same way with batched
+                batched output.
-                output.
 
                 </Tip>
 
         Returns:
-            [`~models.wav2vec2.Wav2Vec2DecoderWithLMOutput`] or `tuple`.
+            [`~models.wav2vec2.Wav2Vec2DecoderWithLMOutput`].
 
+        Example:
+            See [Decoding multiple audios](#decoding-multiple-audios).
         """
+
         from pyctcdecode.constants import (
             DEFAULT_BEAM_WIDTH,
             DEFAULT_HOTWORD_WEIGHT,
@@ -364,11 +386,34 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
         # create multiprocessing pool and list numpy arrays
         # filter out logits padding
         logits_list = [array[(array != -100.0).all(axis=-1)] for array in logits]
-        pool = get_context("fork").Pool(num_processes)
+
+        # create a pool if necessary while also using it as a context manager to close itself
+        if pool is None:
+            # fork is safe to use only on Unix, see "Contexts and start methods" section on
+            # multiprocessing's docs (https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods)
+            default_context = get_start_method()
+
+            if default_context == "fork":
+                cm = pool = get_context().Pool(num_processes)
+            else:
+                logger.warning(
+                    "Parallel batch decoding is not currently supported in this platform. "
+                    "Falling back to sequential decoding."
+                )
+                cm = nullcontext()
+        else:
+            # pool is managed by the user, so we don't need to close it
+            cm = nullcontext()
+
+            if num_processes is not None:
+                logger.warning(
+                    "Parameter `num_process` was passed, but it will be ignored since `pool` was also specified."
+                )
 
         # pyctcdecode
+        with cm:
             decoded_beams = self.decoder.decode_beams_batch(
-            pool,
+                pool=pool,
                 logits_list=logits_list,
                 beam_width=beam_width,
                 beam_prune_logp=beam_prune_logp,
@@ -377,9 +422,6 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
                 hotword_weight=hotword_weight,
             )
 
-        # clone multi-processing pool
-        pool.close()
-
         # extract text and scores
         batch_texts, logit_scores, lm_scores, word_offsets = [], [], [], []
         for d in decoded_beams:
@@ -440,13 +482,12 @@ class Wav2Vec2ProcessorWithLM(ProcessorMixin):
 
                 <Tip>
 
-                Please take a look at the example of [`~models.wav2vec2_with_lm.processing_wav2vec2_with_lm.decode`] to
+                Please take a look at the example below to better understand how to make use of `output_word_offsets`.
-                better understand how to make use of `output_word_offsets`.
 
                 </Tip>
 
         Returns:
-            [`~models.wav2vec2.Wav2Vec2DecoderWithLMOutput`] or `tuple`.
+            [`~models.wav2vec2.Wav2Vec2DecoderWithLMOutput`].
 
         Example:
 

src/transformers/processing_utils.py

@@ -99,8 +99,8 @@ class ProcessorMixin(PushToHubMixin):
         <Tip>
 
         This class method is simply calling [`~feature_extraction_utils.FeatureExtractionMixin.save_pretrained`] and
-        [`~tokenization_utils_base.PreTrainedTokenizer.save_pretrained`]. Please refer to the docstrings of the methods
+        [`~tokenization_utils_base.PreTrainedTokenizerBase.save_pretrained`]. Please refer to the docstrings of the
-        above for more information.
+        methods above for more information.
 
         </Tip>
 

tests/models/wav2vec2/test_modeling_flax_wav2vec2.py

@@ -14,6 +14,7 @@
 
 import inspect
 import math
+import multiprocessing
 import unittest
 
 import numpy as np
@@ -21,6 +22,7 @@ from datasets import load_dataset
 
 from transformers import Wav2Vec2Config, is_flax_available
 from transformers.testing_utils import (
+    CaptureLogger,
     is_flaky,
     is_librosa_available,
     is_pt_flax_cross_test,
@@ -53,6 +55,7 @@ if is_flax_available():
 
 if is_pyctcdecode_available():
     from transformers import Wav2Vec2ProcessorWithLM
+    from transformers.models.wav2vec2_with_lm import processing_wav2vec2_with_lm
 
 
 if is_librosa_available():
@@ -554,3 +557,58 @@ class FlaxWav2Vec2ModelIntegrationTest(unittest.TestCase):
         transcription = processor.batch_decode(np.array(logits)).text
 
         self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")
+
+    @require_pyctcdecode
+    @require_librosa
+    def test_wav2vec2_with_lm_pool(self):
+        ds = load_dataset("common_voice", "es", split="test", streaming=True)
+        sample = next(iter(ds))
+
+        resampled_audio = librosa.resample(sample["audio"]["array"], 48_000, 16_000)
+
+        model = FlaxWav2Vec2ForCTC.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+        processor = Wav2Vec2ProcessorWithLM.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+
+        input_values = processor(resampled_audio, return_tensors="np").input_values
+
+        logits = model(input_values).logits
+
+        # test user-managed pool
+        with multiprocessing.get_context("fork").Pool(2) as pool:
+            transcription = processor.batch_decode(logits.numpy(), pool).text
+
+        self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")
+
+        # user-managed pool + num_processes should trigger a warning
+        with CaptureLogger(processing_wav2vec2_with_lm.logger) as cl, multiprocessing.get_context("fork").Pool(
+            2
+        ) as pool:
+            transcription = processor.batch_decode(logits.numpy(), pool, num_processes=2).text
+
+        self.assertIn("num_process", cl.out)
+        self.assertIn("it will be ignored", cl.out)
+
+        self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")
+
+    @require_pyctcdecode
+    @require_librosa
+    def test_wav2vec2_with_lm_invalid_pool(self):
+        ds = load_dataset("common_voice", "es", split="test", streaming=True)
+        sample = next(iter(ds))
+
+        resampled_audio = librosa.resample(sample["audio"]["array"], 48_000, 16_000)
+
+        model = FlaxWav2Vec2ForCTC.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+        processor = Wav2Vec2ProcessorWithLM.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+
+        input_values = processor(resampled_audio, return_tensors="np").input_values
+
+        logits = model(input_values).logits
+
+        # change default start method, which should trigger a warning if different than fork
+        multiprocessing.set_start_method("spawn")
+        with CaptureLogger(processing_wav2vec2_with_lm.logger) as cl:
+            transcription = processor.batch_decode(logits.numpy()).text
+
+        self.assertIn("Falling back to sequential decoding.", cl.out)
+        self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")

tests/models/wav2vec2/test_modeling_tf_wav2vec2.py

@@ -18,6 +18,7 @@ import copy
 import glob
 import inspect
 import math
+import multiprocessing
 import unittest
 
 import numpy as np
@@ -26,7 +27,7 @@ from datasets import load_dataset
 
 from huggingface_hub import snapshot_download
 from transformers import Wav2Vec2Config, is_tf_available
-from transformers.testing_utils import is_flaky, require_librosa, require_pyctcdecode, require_tf, slow
+from transformers.testing_utils import CaptureLogger, is_flaky, require_librosa, require_pyctcdecode, require_tf, slow
 from transformers.utils import is_librosa_available, is_pyctcdecode_available
 
 from ...test_configuration_common import ConfigTester
@@ -42,6 +43,7 @@ if is_tf_available():
 
 if is_pyctcdecode_available():
     from transformers import Wav2Vec2ProcessorWithLM
+    from transformers.models.wav2vec2_with_lm import processing_wav2vec2_with_lm
 
 
 if is_librosa_available():
@@ -590,3 +592,56 @@ class TFWav2Vec2ModelIntegrationTest(unittest.TestCase):
         transcription = processor.batch_decode(logits.numpy()).text
 
         self.assertEqual(transcription[0], "el libro ha sido escrito por cervantes")
+
+    @require_pyctcdecode
+    @require_librosa
+    def test_wav2vec2_with_lm_pool(self):
+        downloaded_folder = snapshot_download("patrickvonplaten/common_voice_es_sample")
+        file_path = glob.glob(downloaded_folder + "/*")[0]
+        sample = librosa.load(file_path, sr=16_000)[0]
+
+        model = TFWav2Vec2ForCTC.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+        processor = Wav2Vec2ProcessorWithLM.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+
+        input_values = processor(sample, return_tensors="tf").input_values
+
+        logits = model(input_values).logits
+
+        # test user-managed pool
+        with multiprocessing.get_context("fork").Pool(2) as pool:
+            transcription = processor.batch_decode(logits.numpy(), pool).text
+
+        self.assertEqual(transcription[0], "el libro ha sido escrito por cervantes")
+
+        # user-managed pool + num_processes should trigger a warning
+        with CaptureLogger(processing_wav2vec2_with_lm.logger) as cl, multiprocessing.get_context("fork").Pool(
+            2
+        ) as pool:
+            transcription = processor.batch_decode(logits.numpy(), pool, num_processes=2).text
+
+        self.assertIn("num_process", cl.out)
+        self.assertIn("it will be ignored", cl.out)
+
+        self.assertEqual(transcription[0], "el libro ha sido escrito por cervantes")
+
+    @require_pyctcdecode
+    @require_librosa
+    def test_wav2vec2_with_lm_invalid_pool(self):
+        downloaded_folder = snapshot_download("patrickvonplaten/common_voice_es_sample")
+        file_path = glob.glob(downloaded_folder + "/*")[0]
+        sample = librosa.load(file_path, sr=16_000)[0]
+
+        model = TFWav2Vec2ForCTC.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+        processor = Wav2Vec2ProcessorWithLM.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+
+        input_values = processor(sample, return_tensors="tf").input_values
+
+        logits = model(input_values).logits
+
+        # change default start method, which should trigger a warning if different than fork
+        multiprocessing.set_start_method("spawn")
+        with CaptureLogger(processing_wav2vec2_with_lm.logger) as cl:
+            transcription = processor.batch_decode(logits.numpy()).text
+
+        self.assertIn("Falling back to sequential decoding.", cl.out)
+        self.assertEqual(transcription[0], "el libro ha sido escrito por cervantes")

tests/models/wav2vec2/test_modeling_wav2vec2.py

@@ -15,6 +15,7 @@
 """ Testing suite for the PyTorch Wav2Vec2 model. """
 
 import math
+import multiprocessing
 import os
 import pickle
 import tempfile
@@ -25,6 +26,7 @@ from datasets import load_dataset
 
 from transformers import Wav2Vec2Config, is_torch_available
 from transformers.testing_utils import (
+    CaptureLogger,
     is_pt_flax_cross_test,
     is_pyctcdecode_available,
     is_torchaudio_available,
@@ -74,6 +76,7 @@ if is_torchaudio_available():
 
 if is_pyctcdecode_available():
     from transformers import Wav2Vec2ProcessorWithLM
+    from transformers.models.wav2vec2_with_lm import processing_wav2vec2_with_lm
 
 
 if is_torch_fx_available():
@@ -1611,6 +1614,71 @@ class Wav2Vec2ModelIntegrationTest(unittest.TestCase):
 
         self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")
 
+    @require_pyctcdecode
+    @require_torchaudio
+    def test_wav2vec2_with_lm_pool(self):
+        ds = load_dataset("common_voice", "es", split="test", streaming=True)
+        sample = next(iter(ds))
+
+        resampled_audio = torchaudio.functional.resample(
+            torch.tensor(sample["audio"]["array"]), 48_000, 16_000
+        ).numpy()
+
+        model = Wav2Vec2ForCTC.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm").to(
+            torch_device
+        )
+        processor = Wav2Vec2ProcessorWithLM.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+
+        input_values = processor(resampled_audio, return_tensors="pt").input_values
+
+        with torch.no_grad():
+            logits = model(input_values.to(torch_device)).logits
+
+        # test user-managed pool
+        with multiprocessing.get_context("fork").Pool(2) as pool:
+            transcription = processor.batch_decode(logits.numpy(), pool).text
+
+        self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")
+
+        # user-managed pool + num_processes should trigger a warning
+        with CaptureLogger(processing_wav2vec2_with_lm.logger) as cl, multiprocessing.get_context("fork").Pool(
+            2
+        ) as pool:
+            transcription = processor.batch_decode(logits.numpy(), pool, num_processes=2).text
+
+        self.assertIn("num_process", cl.out)
+        self.assertIn("it will be ignored", cl.out)
+
+        self.assertEqual(transcription[0], "bien y qué regalo vas a abrir primero")
+
+    @require_pyctcdecode
+    @require_torchaudio
+    def test_wav2vec2_with_lm_invalid_pool(self):
+        ds = load_dataset("common_voice", "es", split="test", streaming=True)
+        sample = next(iter(ds))
+
+        resampled_audio = torchaudio.functional.resample(
+            torch.tensor(sample["audio"]["array"]), 48_000, 16_000
+        ).numpy()
+
+        model = Wav2Vec2ForCTC.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm").to(
+            torch_device
+        )
+        processor = Wav2Vec2ProcessorWithLM.from_pretrained("patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm")
+
+        input_values = processor(resampled_audio, return_tensors="pt").input_values
+
+        with torch.no_grad():
+            logits = model(input_values.to(torch_device)).logits
+
+        # change default start method, which should trigger a warning if different than fork
+        multiprocessing.set_start_method("spawn")
+        with CaptureLogger(processing_wav2vec2_with_lm.logger) as cl:
+            transcription = processor.batch_decode(logits.numpy()).text
+
+        self.assertIn("Falling back to sequential decoding.", cl.out)
+        self.assertEqual(transcription[0], "el libro ha sido escrito por cervantes")
+
     def test_inference_diarization(self):
         model = Wav2Vec2ForAudioFrameClassification.from_pretrained("anton-l/wav2vec2-base-superb-sd").to(torch_device)
         processor = Wav2Vec2FeatureExtractor.from_pretrained("anton-l/wav2vec2-base-superb-sd")

tests/models/wav2vec2_with_lm/test_processor_wav2vec2_with_lm.py

@@ -25,6 +25,7 @@ import numpy as np
 from datasets import load_dataset
 from packaging import version
 
+from parameterized import parameterized
 from transformers import AutoProcessor
 from transformers.models.wav2vec2 import Wav2Vec2CTCTokenizer, Wav2Vec2FeatureExtractor
 from transformers.models.wav2vec2.tokenization_wav2vec2 import VOCAB_FILES_NAMES
@@ -194,7 +195,8 @@ class Wav2Vec2ProcessorWithLMTest(unittest.TestCase):
         self.assertEqual(decoded_decoder[-2], decoded_processor.logit_score)
         self.assertEqual(decoded_decoder[-1], decoded_processor.lm_score)
 
-    def test_decoder_batch(self):
+    @parameterized.expand([[None], ["fork"], ["spawn"]])
+    def test_decoder_batch(self, pool_context):
         feature_extractor = self.get_feature_extractor()
         tokenizer = self.get_tokenizer()
         decoder = self.get_decoder()
@@ -203,17 +205,25 @@ class Wav2Vec2ProcessorWithLMTest(unittest.TestCase):
 
         logits = self._get_dummy_logits()
 
+        # note: pool should be instantiated *after* Wav2Vec2ProcessorWithLM.
+        #       otherwise, the LM won't be available to the pool's sub-processes.
+        # manual logic used to allow parameterized test for both pool=None and pool=Pool(...)
+        if pool_context is None:
             decoded_processor = processor.batch_decode(logits)
+        else:
+            with get_context(pool_context).Pool() as pool:
+                decoded_processor = processor.batch_decode(logits, pool)
 
         logits_list = [array for array in logits]
-        pool = get_context("fork").Pool()
+
-        decoded_beams = decoder.decode_beams_batch(pool, logits_list)
+        with get_context("fork").Pool() as p:
+            decoded_beams = decoder.decode_beams_batch(p, logits_list)
+
         texts_decoder, logit_scores_decoder, lm_scores_decoder = [], [], []
         for beams in decoded_beams:
             texts_decoder.append(beams[0][0])
             logit_scores_decoder.append(beams[0][-2])
             lm_scores_decoder.append(beams[0][-1])
-        pool.close()
 
         self.assertListEqual(texts_decoder, decoded_processor.text)
         self.assertListEqual(["<s> <s> </s>", "<s> <s> <s>"], decoded_processor.text)
@@ -242,7 +252,8 @@ class Wav2Vec2ProcessorWithLMTest(unittest.TestCase):
         decoded_processor = decoded_processor_out.text
 
         logits_list = [array for array in logits]
-        pool = get_context("fork").Pool()
+
+        with get_context("fork").Pool() as pool:
             decoded_decoder_out = decoder.decode_beams_batch(
                 pool,
                 logits_list,
@@ -250,7 +261,6 @@ class Wav2Vec2ProcessorWithLMTest(unittest.TestCase):
                 beam_prune_logp=beam_prune_logp,
                 token_min_logp=token_min_logp,
             )
-        pool.close()
 
         decoded_decoder = [d[0][0] for d in decoded_decoder_out]
 
@@ -287,12 +297,12 @@ class Wav2Vec2ProcessorWithLMTest(unittest.TestCase):
             unk_score_offset=unk_score_offset,
             lm_score_boundary=lm_score_boundary,
         )
-        pool = get_context("fork").Pool()
+
+        with get_context("fork").Pool() as pool:
             decoded_decoder_out = decoder.decode_beams_batch(
                 pool,
                 logits_list,
             )
-        pool.close()
 
         decoded_decoder = [d[0][0] for d in decoded_decoder_out]