[logging] autoflush

[stas00]

This PR proposes to:

• auto-flush transformers logging

When using logging for tracing signals from different parts of the code and which could be mixed with print debug this aids to get all the logging events synchronized.

I don't think this change will introduce any performance impacts.

If it helps someone here is the code I used to sync transformers logging with various other debug prints.

I was porting bart to MP and I needed to trace that the device switching happens correctly and I added a bunch of logger.info calls inside modeling_bart.py and also had some other helpers print debug messages which weren't logger based:

# auto flush std streams
from sys import stdout, stderr
def stdout_write_flush(args, w=stderr.write): w(args); stderr.flush()
def stderr_write_flush(args, w=stderr.write): w(args); stderr.flush()
stdout.write = stdout_write_flush
stderr.write = stderr_write_flush

from transformers import BartTokenizer, BartForConditionalGeneration, BartConfig

import logging
import transformers.utils.logging
import transformers.models.bart.modeling_bart

# I wanted a shorter simpler format
handlers = transformers.utils.logging._get_library_root_logger().handlers
for handler in handlers:
    formatter = logging.Formatter("[%(funcName)s] %(message)s")
    handler.setFormatter(formatter)

transformers.models.bart.modeling_bart.logger.setLevel(transformers.logging.INFO)

# then all the model creation and generate() goes next

@LysandreJik, @sgugger, @patrickvonplaten

[patrickvonplaten]

Nice! LGTM - think @LysandreJik knows best here

[sgugger]

LGTM but let's wait for the logging master ;-)

[LysandreJik]

Yes, this is a welcome change, LGTM! Thanks @stas00.