Add sox_effects submodule and delegate sox_effects init/shutdown (#708)

There are couple of aspects of this PR that overall improves the maintainability of the code base, based on "decoupling" and "separation of concerns".

First, `sox_effects` functionalities can be either available or unavailable. From the viewpoint of `torchaudio` main module, the looser the connection between the `torchaudio` module and `torchaudio.sox_effects`, the more manageable the code base become because you can change the two modules independently. This is mostly accomplished when the definitions of `initialize_sox` and `shutdown_sox` were moved from `torchaudio.__init__` to `torchaudio.sox_effects`, but the initialization of sox effects are still happening in `torchaudio.__init__`. If we move the initialization to `sox_effects` module, the responsibility of sox initialization is moved to `sox_effects` module, along with the required module availability check etc. The main `torchaudio` module can be carefree about how the `sox_effects` module should work.

In addition to that, I found that `initialize_sox` and `shutdown_sox` are confusing because it sound like they are required for `libsox` based I/O. To make it clear, I renamed them to include `sox_effect` in function name.

Also moving functions from the original places are BC breaking itself, therefore, these functions are re-imported in `torchaudio.__init__` and renamed to match the original names. Therefore the PR is not BC breaking.

torchaudio/__init__.py

@@ -23,11 +23,10 @@ from torchaudio.backend import (
     SignalInfo,
     EncodingInfo,
 )
-from torchaudio._internal import (
-    module_utils as _mod_utils,
-    misc_ops as _misc_ops,
+from torchaudio.sox_effects import (
+    init_sox_effects as initialize_sox,
+    shutdown_sox_effects as shutdown_sox,
 )
-from torchaudio.sox_effects import initialize_sox, shutdown_sox
 
 try:
     from .version import __version__, git_version  # noqa: F401
@@ -35,11 +34,6 @@ except ImportError:
     pass
 
 
-if _mod_utils.is_module_available('torchaudio._torchaudio'):
-    from . import _torchaudio
-    initialize_sox()
-
-
 def load(filepath: Union[str, Path],
          out: Optional[Tensor] = None,
          normalization: Union[bool, float, Callable] = True,

torchaudio/sox_effects/__init__.py

+from torchaudio._internal import module_utils as _mod_utils
+from .sox_effects import (
+    init_sox_effects,
+    shutdown_sox_effects,
+    effect_names,
+    SoxEffect,
+    SoxEffectsChain,
+)
+
+
+if _mod_utils.is_module_available('torchaudio._torchaudio'):
+    init_sox_effects()

torchaudio/sox_effects.py → torchaudio/sox_effects/sox_effects.py

@@ -2,7 +2,6 @@ import atexit
 from typing import Any, Callable, List, Optional, Tuple, Union
 
 import torch
-import torchaudio
 from torch import Tensor
 
 from torchaudio._internal import (
@@ -11,7 +10,7 @@ from torchaudio._internal import (
 )
 
 if _mod_utils.is_module_available('torchaudio._torchaudio'):
-    from . import _torchaudio
+    from torchaudio import _torchaudio
 
 
 _SOX_INITIALIZED: Optional[bool] = False
@@ -26,7 +25,7 @@ _SOX_SUCCESS_CODE = 0
 
 
 @_mod_utils.requires_module('torchaudio._torchaudio')
-def initialize_sox() -> int:
+def init_sox_effects() -> int:
     """Initialize sox for use with effects chains.
 
     You only need to call this function once to use SoX effects chains multiple times.
@@ -48,13 +47,13 @@ def initialize_sox() -> int:
         code = _torchaudio.initialize_sox()
         if code == _SOX_SUCCESS_CODE:
             _SOX_INITIALIZED = True
-            atexit.register(shutdown_sox)
+            atexit.register(shutdown_sox_effects)
         return code
     return _SOX_SUCCESS_CODE
 
 
 @_mod_utils.requires_module("torchaudio._torchaudio")
-def shutdown_sox() -> int:
+def shutdown_sox_effects() -> int:
     """Showdown sox for effects chain.
 
     You do not need to call this function as it will be called automatically