Re: [Boost-users] Atomic boost::filesystem::rename

Subject: Re: [Boost-users] Atomic boost::filesystem::rename
From: Gavin Lambert (boost_at_[hidden])
Date: 2019-01-15 22:37:20

On 16/01/2019 09:02, Lars wrote:
> What is the most "atomic" way to move two files from a local disk to a 
> server location? The meaning of atomic in this context means that either 
> both files are moved or both files stay in original location. No 
> intermediate files should be present once operation is finished.

When you detect that the source and target are on different filesystems, 
you should first perform a regular copy of the file to the target 
filesystem (using a different filename).  Then perform the rename from 
this temporary file to the actual target filename.

Usually you can put the temporary file in the same target directory but 
with a different file pattern that you know will not be observed by 
consuming directory watchers.  If watchers might be looking for all 
files, then you may need to put temporary files in a different 
directory, as long as it's on the same filesystem.

Using the same target directory also reduces the risk of permissions 
problems, although whatever installation process you use can require 
that the target directory and the temp directory have the same 
permissions, along with ensuring that they're suitably configured so 
your app can find them in the first place.