Consider a variant of deleteFile that on Windows retries x times before giving up

[Mistuke]

As discussed in haskell/hsc2hs#25 there are various services on Windows that can keep a file open for a fraction of time, such as indexer or AV services. That means that deleteFile may fail temporarily.

It's a reasonably common idiom, SQLlite for instance does so as well https://www.sqlite.org/src/info/89f1848d7f and we do it in the GHC testsuite and now hsc2hs to avoid a race condition with the file deletion.

Would it be perhaps handy to have such a function in Directory?

[Rufflewind]

It's not a very elegant solution, but I guess it's kind of needed on Windows. I would suggest making a somewhat generic retry function if possible, as there are many variants of removeFileThing:

retryOnPermissionError :: {- numRetries -} Int -> IO a -> IO a

[Rufflewind]

Is there still interest in this feature?

[Mistuke]

Is there still interest in this feature?

Yes, it's used in GHC, hsc2hs, cabal and GHC's testsuite. So it would allow us to align those implementations and I believe it's useful for third parties as well. But I honestly don't know when I would personally have the time to implement this.

[hasufell]

retryOnPermissionError :: {- numRetries -} Int -> IO a -> IO a

I think the wording is problematic. Afais, the exceptions to retry on are ERROR_LOCK_VIOLATION and ERROR_SHARING_VIOLATION, which are very specific. And we don't know if that will change or if there are more use cases for this for some users. Code-paths that rely on exception types are very very fragile.

I would go so far to say this doesn't belong in this library, but is a generic exception handling function and already exists in various forms, such as retryBool.

The documentation of removeFile should simply document this behavior. That's what the python sdtlib does as well.

[Rufflewind]

I'm inclined to agree with @hasufell that this might be getting a bit out of scope for this library. A general retry function probably belongs to System.IO.Exception or similar.

Closing this issue for now. Let me know if there are any concerns.