create_dir_all is not thread safe

[weiznich]

For concurrent requests to create the same directory using create_dir_all it is possible that the request fails with Error { repr: Os { code: 17, message: "File exists" } because a second thread already has created that directory. The problem is caused by create_dir_all function in DirBuilder.

I see three solution for this problem:

1. Document this behaviour
2. Make create_dir_all
3. Make create_dir_all ignoring this error?

Platform: Ubuntu 16.04 x86_64

[durka]

Duplicate of #33707.

[alexcrichton]

Indeed!