Problem reading file immediately after writing

[Joanna Carter]

Hi folks

I need to change the exif:orientation tag on a file and then, immediately, use a thumbnail generator to fetch the freshly rotated image.

At the moment, the only way I can get things to work is to introduce a delay immediately after writing.

I presume this is due to the overwriting of of the safety copy, etc.

Is there any way to get a callback when the safety stuff has completed?

This becomes even more problematic if I want to select multiple files.

[Joanna Carter]

Hello - is there anybody there?

[StarGeek]

This will require Phil's attention as it is beyond my knowledge.  I suspect he is having very good weather and is out birding.

[Joanna Carter]

I suspect he is having very good weather and is out birding

I don't know - these part-time workers 

[greybeard]

You might need to share your code - just enough to show the problem

[Joanna Carter]

I doubt if that is going to help. It is written in Swift for a macOS app and it calls two functions in sequence...

Code Select Expand


            try? ExifWriter.writeOrientation(rotatedOrientation, for: [url])
           
            thumbnailItem.reloadImage()


The first function constructs and executes an ExifTool command line, the second function calls Apple's QLThumbnailGenerator to construct and return a thumbnail image.

Neither function is simple and showing their many lines of code is unlikely to reveal anything more.

Suffice to say that the second function needs to contain a call that delays the retrieval of the thumbnail in order to avoid the ExifTool command not having executed completely.

Code Select Expand


DispatchQueue.main.asyncAfter(deadline: .now() + 1)
    {
      ...


My guess is that ExifTool is tidying up the backup file on a background thread, but there appears to be no completion callback that I can hook into.

[Joanna Carter]

Hi folks

I've found the solution to the problem

Apple have now changed their Process class by deprecating the launch() function, which is asynchronous, and providing a completion handler, which is called after the process has fully run.

Happy days!!!

[greybeard]

the Process terminationHandler should do what you need - I don't think this problem is specific to exiftool

[Joanna Carter]

You are absolutely right. It was something that I didn't find or need a couple of years ago when I started with this app.

Everything worked perfectly before because I had no need to reload the image until I added in the orientation code.

I have been using Xcode for many years and have published apps but, still, there is stuff that seems determined to hide from us as developers