[TECHNICAL] Improve performance in main-thread operations

[nbd-boss]

Dear developers,

I am analyzing owncloud using a static code checker. I found some potential slow operations in owncloud's UI thread.

Android documentation says this:

http://developer.android.com/training/articles/perf-anr.html

"Any method that runs in the UI thread should do as little work as possible on that thread. In particular, activities should do as little as possible in key life-cycle methods such as onCreate(). Potentially long running operations such as network or database operations, or computationally expensive calculations such as resizing bitmaps should be done in a worker thread (e.g., via AsyncTask)."

I've identified the following operations running on the UI thread that may cause performance issues:

1. File system I/O:
   ReceiveExternalFilesActivity.onCreate() synchronously invokes prepareStreamsToUpload(), which performs blocking file system operations (e.g., calling File.getCanonicalPath()).
2. Database I/O:
   FolderPickerActivity.onCreate() synchronously invokes initAndShowListOfFilesFragment(), which triggers disk I/O by querying the local SQLite database via FileDataStorageManager.getFileByPath().

Do you think these slow operations will affect owncloud's performance (e.g., make GUI not smooth enough)? If yes, perhaps moving them to a separate thread can help make owncloud super smooth in user interaction. Looking forward to your reply and hope I can help improve owncloud.

[joragua]

Hi @nbd-boss! Thanks for opening a new issue 🍻

Yes, as you mentioned, all of these operations could potentially affect owCloud's performance. Long operations (like network or database operations) should not run on the main thread. Some of the code you pointed out was created several years ago 🤔 (since 2015...) by different developers, which might explain why the application is structured this way. Anyway, we will keep this issue on our radar, but addressing it will require significant research and refactoring (there are probably more methods that can be refactored besides the ones mentioned)

In any case, if you would like to contribute to the project, you are welcome to create a PR with your changes! If you have any questions, feel free to reach out! 😄