[Fix] Fix the permission denied error on windows.

[fjfzlzj]

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Motivation

To fix the permission denied error when using '--resuming-from' on Windows. [#1063] [#4966(mmdet)]
I'm not sure whether that modification will cause any problems on other platforms or not, so I add an 'if' to ensure Windows only.

Modification

Modify the behavior of loading config on Windows:

• Temporary file now will be closed without being deleted before reading on Windows.
• When read ends, it will be deleted by os.unlink.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Merging #1077 (9b51959) into master (d212bd5) will increase coverage by 1.92%.
The diff coverage is 100.00%.

❗ Current head 9b51959 differs from pull request most recent head e9c54ad. Consider uploading reports for the commit e9c54ad to get more accurate results

@@            Coverage Diff             @@
##           master    #1077      +/-   ##
==========================================
+ Coverage   65.72%   67.64%   +1.92%     
==========================================
  Files         157      159       +2     
  Lines       10092    10281     +189     
  Branches     1828     1856      +28     
==========================================
+ Hits         6633     6955     +322     
+ Misses       3113     2961     -152     
- Partials      346      365      +19     

Flag	Coverage Δ
unittests	67.64% <100.00%> (+1.92%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmcv/utils/config.py	89.88% <100.00%> (+0.02%)	⬆️
mmcv/ops/multi_scale_deform_attn.py	58.40% <0.00%> (-11.29%)	⬇️
mmcv/utils/ext_loader.py	35.89% <0.00%> (-2.34%)	⬇️
mmcv/runner/fp16_utils.py	58.12% <0.00%> (-1.61%)	⬇️
mmcv/runner/hooks/optimizer.py	16.66% <0.00%> (-1.08%)	⬇️
mmcv/ops/__init__.py	100.00% <0.00%> (ø)
mmcv/cnn/bricks/__init__.py	100.00% <0.00%> (ø)
mmcv/cnn/bricks/registry.py	100.00% <0.00%> (ø)
mmcv/runner/hooks/logger/__init__.py	100.00% <0.00%> (ø)
mmcv/runner/hooks/logger/dvclive.py	86.36% <0.00%> (ø)
... and 7 more

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[wangruohui]

As a suggestion, a cleaner way is :

with tempfile.NamedTemporaryFile('w', delete=False, suffix=file_format) as temp_file:
    temp_file.write(cfg_str)
cfg = Config.fromfile(temp_file.name)
# see PR #1077 for more detail
os.unlink(temp_file.name)

This should work for both windows and linux.
The reason is not "the file is deleted when reading", instead , the reason is that, on windows, a file cannot be opened twice. Here, temp_file is opened first in the with statement and second in function from_file thus resuting the error on windows.

So as a potentially more stable solution, just create the file on disk, run fromfile, then delete it, all manually.

[fjfzlzj]

Thanks for the suggestion. I add [#4966(mmdet)] to comment and modify code as your suggest.

[wangruohui]

good

[zhouzaida]

LGTM

[hellock]

A comment may be left to note windows compatibility.

[OpenMMLab-Coodinator]

Hi @fjfzlzj ！First of all, we want to express our gratitude for your significant PR in this project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.

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