doc for bg_iterator et al

[vincentqb]

The documentation for torchaudio does not include bg_iterator and disk_cache_iterator from code. Thanks to comment to point this out :)

[vincentqb]

Example usage with any iterator:

for i in bg_iterator(some_iterator):
    # do stuff

In particular with data_loader:

for datapoint in bg_iterator(data_loader):
    # training

[faroit]

I evaluated the use of bg_iterator in my pipeline and got almost no speed up regardless which loading backend I used.

@vincentqb Can you share your experience when to expect an improvement using it especially in combination with the number of workers?

[faroit]

furthermore together with torch 1.7 I now get deadlocks when using bg_iterator... simular to this report. Is there anything that could have caused this?

[mthrok]

@vincentqb Do you want to look into this?

[mthrok]

@AzizCode92 found a bug in bg_iterator. It hangs when loading fails. #1126 (comment)

So the bg_iterator is

1. no speed up
2. not documented
3. buggy

I do not think this utility is providing any value, and this is a pure technical debt. I suggest we remove it from the library.