Handle SoX init/shutdown automatically (#572)

* Add safeguard to SoX initialization/shutdown

* Initialize SoX automatically when it's needed

test/common_utils.py

@@ -78,14 +78,3 @@ def filter_backends_with_mp3(backends):
 
 
 BACKENDS_MP3 = filter_backends_with_mp3(BACKENDS)
-
-
-_IS_SOX_INITIALIZED = False
-
-
-def initialize_sox():
-    """Initialize sox backend only if it has not yet."""
-    global _IS_SOX_INITIALIZED
-    if not _IS_SOX_INITIALIZED:
-        torchaudio.initialize_sox()
-        _IS_SOX_INITIALIZED = True

test/test_dataloader.py

@@ -30,10 +30,6 @@ class TORCHAUDIODS(Dataset):
 
 @unittest.skipIf("sox" not in BACKENDS, "sox not available")
 class Test_DataLoader(unittest.TestCase):
-    @classmethod
-    def setUpClass(cls):
-        common_utils.initialize_sox()
-
     def test_1(self):
         expected_size = (2, 1, 16000)
         ds = TORCHAUDIODS()

test/test_sox_effects.py

@@ -11,10 +11,6 @@ from common_utils import AudioBackendScope, BACKENDS
 class Test_SoxEffectsChain(unittest.TestCase):
     test_filepath = common_utils.get_asset_path("steam-train-whistle-daniel_simon.mp3")
 
-    @classmethod
-    def setUpClass(cls):
-        common_utils.initialize_sox()
-
     def test_single_channel(self):
         fn_sine = common_utils.get_asset_path("sinewave.wav")
         E = torchaudio.sox_effects.SoxEffectsChain()

torchaudio/__init__.py

+import atexit
 import os.path
 from pathlib import Path
 from typing import Any, Callable, Optional, Tuple, Union
@@ -338,25 +339,67 @@ def get_sox_bool(i: int = 0) -> Any:
         return _torch_sox.sox_bool(i)
 
 
+_SOX_INITIALIZED = False
+# This variable has a micro lifecycle. (False -> True -> None)
+# False: Not initialized
+# True: Initialized
+# None: Already shut down (should not be initialized again.)
+
+_SOX_SUCCESS_CODE = 0
+# defined at
+# https://fossies.org/dox/sox-14.4.2/sox_8h.html#a8e07e80cebeff3339265d89c387cea93a9ef2b87ec303edfe40751d9a85fadeeb
+
+
 @_audio_backend_guard("sox")
 def initialize_sox() -> int:
-    """Initialize sox for use with effects chains.  This is not required for simple
-    loading.  Importantly, only run `initialize_sox` once and do not shutdown
-    after each effect chain, but rather once you are finished with all effects chains.
-    """
+    """Initialize sox for use with effects chains.
 
+    You only need to call this function once to use SoX effects chains multiple times.
+    It is safe to call this function multiple times as long as ``shutdown_sox`` is not yet called.
+    Once ``shutdown_sox`` is called, you can no longer use SoX effects and calling this function
+    results in `RuntimeError`.
+
+    Note:
+        This function is not required for simple loading.
+
+    Returns:
+        int: Code corresponding to sox_error_t enum. See
+        https://fossies.org/dox/sox-14.4.2/sox_8h.html#a8e07e80cebeff3339265d89c387cea93
+    """
+    global _SOX_INITIALIZED
+    if _SOX_INITIALIZED is None:
+        raise RuntimeError('SoX effects chain has been already shut down. Can not initialize again.')
+    if not _SOX_INITIALIZED:
         import _torch_sox
-    return _torch_sox.initialize_sox()
+        code = _torch_sox.initialize_sox()
+        if code == _SOX_SUCCESS_CODE:
+            _SOX_INITIALIZED = True
+            atexit.register(shutdown_sox)
+        return code
+    return _SOX_SUCCESS_CODE
 
 
 @_audio_backend_guard("sox")
 def shutdown_sox() -> int:
-    """Showdown sox for effects chain.  Not required for simple loading.  Importantly,
-    only call once.  Attempting to re-initialize sox will result in seg faults.
-    """
+    """Showdown sox for effects chain.
+
+    You do not need to call this function as it will be called automatically
+    at the end of program execution, if ``initialize_sox`` was called.
 
+    It is safe to call this function multiple times.
+
+    Returns:
+        int: Code corresponding to sox_error_t enum. See
+        https://fossies.org/dox/sox-14.4.2/sox_8h.html#a8e07e80cebeff3339265d89c387cea93
+    """
+    global _SOX_INITIALIZED
+    if _SOX_INITIALIZED:
         import _torch_sox
-    return _torch_sox.shutdown_sox()
+        code = _torch_sox.shutdown_sox()
+        if code == _SOX_INITIALIZED:
+            _SOX_INITIALIZED = None
+        return code
+    return _SOX_SUCCESS_CODE
 
 
 def _audio_normalization(signal: Tensor, normalization: Union[bool, float, Callable]) -> None:

torchaudio/sox_effects.py

@@ -149,6 +149,7 @@ class SoxEffectsChain(object):
 
         # print("effect options:", [x.eopts for x in self.chain])
 
+        torchaudio.initialize_sox()
         import _torch_sox
         sr = _torch_sox.build_flow_effects(self.input_file,
                                            out,