[BC-Breaking] Remove legacy global backend switch (#3559)

Summary:
This PR removes the legacy backend switch mechanism.
The implementation itself is still available.

Merge after v2.1 release

Pull Request resolved: https://github.com/pytorch/audio/pull/3559

Reviewed By: nateanl

Differential Revision: D48353764

Pulled By: mthrok

fbshipit-source-id: 4d3924dbe6f334ecebe2b12fcd4591c61c4aa656

docs/source/torchaudio.rst

@@ -17,6 +17,7 @@ it easy to handle audio data.
    info
    load
    save
+   list_audio_backends
 
 .. _backend:
 
@@ -91,30 +92,12 @@ please refer to https://github.com/pytorch/audio/issues/2950
 * In 2.0, audio I/O backend dispatcher was introduced.
   Users can opt-in to using dispatcher by setting the environment variable
   ``TORCHAUDIO_USE_BACKEND_DISPATCHER=1``.
-* In 2.1, the disptcher becomes the default mechanism for I/O.
-  Those who need to keep using the previous mechanism (global backend) can do
-  so by setting ``TORCHAUDIO_USE_BACKEND_DISPATCHER=0``.
-* In 2.2, the legacy global backend mechanism will be removed.
+* In 2.1, the disptcher became the default mechanism for I/O.
+* In 2.2, the legacy global backend mechanism is removed.
   Utility functions :py:func:`get_audio_backend` and :py:func:`set_audio_backend`
-  become no-op.
+  became no-op.
 
-Furthermore, we are removing file-like object support from libsox backend, as this
+Furthermore, we removed file-like object support from libsox backend, as this
 is better supported by FFmpeg backend and makes the build process simpler.
 Therefore, beginning with 2.1, FFmpeg and Soundfile are the sole backends that support
 file-like objects.
-
-Backend Utilities
------------------
-
-The following functions are effective only when backend dispatcher is disabled.
-
-Note that the changes in 2.1 marks :py:func:`get_audio_backend` and
-:py:func:`set_audio_backend` deprecated.
-
-.. autosummary::
-   :toctree: generated
-   :nosignatures:
-
-   list_audio_backends
-   get_audio_backend
-   set_audio_backend

test/torchaudio_unittest/backend/utils_test.py

-import torchaudio
-from torchaudio_unittest import common_utils
-
-
-class BackendSwitchMixin:
-    """Test set/get_audio_backend works"""
-
-    backend = None
-    backend_module = None
-
-    def test_switch(self):
-        torchaudio.backend.utils.set_audio_backend(self.backend)
-        if self.backend is None:
-            assert torchaudio.backend.utils.get_audio_backend() is None
-        else:
-            assert torchaudio.backend.utils.get_audio_backend() == self.backend
-        assert torchaudio.load == self.backend_module.load
-        assert torchaudio.save == self.backend_module.save
-        assert torchaudio.info == self.backend_module.info
-
-
-class TestBackendSwitch_NoBackend(BackendSwitchMixin, common_utils.TorchaudioTestCase):
-    backend = None
-    backend_module = torchaudio.backend.no_backend
-
-
-@common_utils.skipIfNoSox
-class TestBackendSwitch_SoXIO(BackendSwitchMixin, common_utils.TorchaudioTestCase):
-    backend = "sox_io"
-    backend_module = torchaudio.backend.sox_io_backend
-
-
-@common_utils.skipIfNoModule("soundfile")
-class TestBackendSwitch_soundfile(BackendSwitchMixin, common_utils.TorchaudioTestCase):
-    backend = "soundfile"
-    backend_module = torchaudio.backend.soundfile_backend

torchaudio/__init__.py

-from . import (  # noqa: F401
+# Initialize extension and backend first
+from . import (  # noqa  # usort: skip
     _extension,
+    _backend,
+)
+from . import (  # noqa: F401
+    backend,  # For BC
     compliance,
     datasets,
     functional,
@@ -11,7 +16,7 @@ from . import (  # noqa: F401
     transforms,
     utils,
 )
-from ._backend.common import AudioMetaData  # noqa
+from ._backend import AudioMetaData, get_audio_backend, info, list_audio_backends, load, save, set_audio_backend
 
 try:
     from .version import __version__, git_version  # noqa: F401
@@ -19,26 +24,11 @@ except ImportError:
     pass
 
 
-def _is_backend_dispatcher_enabled():
-    import os
-
-    return os.getenv("TORCHAUDIO_USE_BACKEND_DISPATCHER", default="1") == "1"
-
-
-if _is_backend_dispatcher_enabled():
-    from ._backend import _init_backend, get_audio_backend, list_audio_backends, set_audio_backend
-else:
-    from .backend import _init_backend, get_audio_backend, list_audio_backends, set_audio_backend
-
-
-_init_backend()
-
-# for backward compatibility. This has to happen after _backend is imported.
-from . import backend  # noqa: F401
-
-
 __all__ = [
     "AudioMetaData",
+    "load",
+    "info",
+    "save",
     "io",
     "compliance",
     "datasets",

torchaudio/_backend/__init__.py

 from typing import List, Optional
 
-import torchaudio
 from torchaudio._internal.module_utils import deprecated
 
+from . import utils
+from .common import AudioMetaData
 
-# TODO: Once legacy global backend is removed, move this to torchaudio.__init__
-def _init_backend():
-    from . import utils
+__all__ = [
+    "AudioMetaData",
+    "load",
+    "info",
+    "save",
+    "list_audio_backends",
+    "get_audio_backend",
+    "set_audio_backend",
+]
 
-    torchaudio.info = utils.get_info_func()
-    torchaudio.load = utils.get_load_func()
-    torchaudio.save = utils.get_save_func()
+
+info = utils.get_info_func()
+load = utils.get_load_func()
+save = utils.get_save_func()
 
 
 def list_audio_backends() -> List[str]:
@@ -24,7 +32,6 @@ def list_audio_backends() -> List[str]:
         - Dispatcher mode: ``"ffmpeg"``, ``"sox"`` and ``"soundfile"``.
         - Legacy backend mode: ``"sox_io"``, ``"soundfile"``.
     """
-    from . import utils
 
     return list(utils.get_available_backends().keys())
 

torchaudio/backend/__init__.py

@@ -3,11 +3,6 @@
 # New things should be added to `torchaudio._backend`.
 # Only things related to backward compatibility should be placed here.
 
-from .utils import _init_backend, get_audio_backend, list_audio_backends, set_audio_backend
-
-
-__all__ = ["_init_backend", "get_audio_backend", "list_audio_backends", "set_audio_backend"]
-
 
 def __getattr__(name: str):
     if name == "common":

torchaudio/backend/_common.py

@@ -7,7 +7,7 @@ def __getattr__(name: str):
             "`torchaudio.AudioMetaData`. Please update the import path.",
             stacklevel=2,
         )
-        from torchaudio._backend.common import AudioMetaData
+        from torchaudio import AudioMetaData
 
         return AudioMetaData
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

torchaudio/backend/utils.py

-"""Defines utilities for switching audio backends"""
-import warnings
-from typing import List, Optional
-
-import torchaudio
-from torchaudio._backend import soundfile_backend
-from torchaudio._internal import module_utils as _mod_utils
-
-from . import _no_backend as no_backend, _sox_io_backend as sox_io_backend
-
-__all__ = [
-    "list_audio_backends",
-    "get_audio_backend",
-    "set_audio_backend",
-]
-
-
-def list_audio_backends() -> List[str]:
-    """List available backends
-
-    Returns:
-        List[str]: The list of available backends.
-    """
-    backends = []
-    if _mod_utils.is_module_available("soundfile"):
-        backends.append("soundfile")
-    if torchaudio._extension._SOX_INITIALIZED:
-        backends.append("sox_io")
-    return backends
-
-
-def set_audio_backend(backend: Optional[str]):
-    """Set the backend for I/O operation
-
-    Args:
-        backend (str or None): Name of the backend.
-            One of ``"sox_io"`` or ``"soundfile"`` based on availability
-            of the system. If ``None`` is provided the  current backend is unassigned.
-    """
-    if backend is not None and backend not in list_audio_backends():
-        raise RuntimeError(f'Backend "{backend}" is not one of ' f"available backends: {list_audio_backends()}.")
-
-    if backend is None:
-        module = no_backend
-    elif backend == "sox_io":
-        module = sox_io_backend
-    elif backend == "soundfile":
-        module = soundfile_backend
-    else:
-        raise NotImplementedError(f'Unexpected backend "{backend}"')
-
-    for func in ["save", "load", "info"]:
-        setattr(torchaudio, func, getattr(module, func))
-
-
-def _init_backend():
-    warnings.warn(
-        "TorchAudio's global backend is now deprecated. "
-        "Please enable distpatcher by setting `TORCHAUDIO_USE_BACKEND_DISPATCHER=1`, "
-        "and specify backend when calling load/info/save function.",
-        stacklevel=3,
-    )
-    backends = list_audio_backends()
-    if "sox_io" in backends:
-        set_audio_backend("sox_io")
-    elif "soundfile" in backends:
-        set_audio_backend("soundfile")
-    else:
-        set_audio_backend(None)
-
-
-def get_audio_backend() -> Optional[str]:
-    """Get the name of the current backend
-
-    Returns:
-        Optional[str]: The name of the current backend or ``None`` if no backend is assigned.
-    """
-    if torchaudio.load == no_backend.load:
-        return None
-    if torchaudio.load == sox_io_backend.load:
-        return "sox_io"
-    if torchaudio.load == soundfile_backend.load:
-        return "soundfile"
-    raise ValueError("Unknown backend.")