Auto-DJ stops when file is missing but cached

[Daniel Schürmann]

TrackInfoObect caches the file exist info.
It may happens that a cached file no longer exists do to a removable media.
In this case, Auto-DJ does not skip the missing track.
The attached patch solves the problem against lp:mixx #3003

[RJ Skerry-Ryan (rryan)]

My main hesitation with the patch is that it makes a method of TIO hit the disk (And QFileInfo is notoriously slow) so if someone called exists() on a ton of TIO's in a loop or if somebody called exists() in the engine callback we would be doing file I/O without realizing it. I looked at all the callers of TIO::exists() and CachingReader calls it but from the CR thread and not from the engine callback. So I think the patch is fine to add.

Could you use QFile::exists() instead of QFileInfo? I think that QFileInfo looks up much more information from the filesystem that we won't use. Hopefully the implementation of QFile::exists() is cheaper.

[Daniel Schürmann (daschuer)]

I have set this bug to triaged, because the patch does not solve the issue for the 1.10 branch.
Furthermore there are some other Auto DJ issues which are more annoying. We should consider if we back port some of the auto DJ parts of 1.11 to 1.10.1 or if we just recommend to upgrade to 1.11 if one wants to use Auto DJ.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/6344