Cannot delete image file passsed to PredictionEngine for Image Classification after disposing the engine

[giuseppe-terrasi]

System information

• OS version/distro: Windows 10 Pro 10.0.18363
• .NET Version (eg., dotnet --info): 3.1.0

Issue

• What did you do?: I've tried to delete an image file used by PredictionEngine after disposing the engine
• What happened?: An exception was thorwn: "The process cannot access the file because it is being used by another process."
• What did you expect?: Image file deletion

Source code / logs

private ImagePrediction ClassifySingleImage(MLContext mLContext, ITransformer model, string imagePath)
{
    var imageData = new ImageData()
    {
        ImagePath = imagePath
    };
    var predictor = mLContext.Model.CreatePredictionEngine<ImageData, ImagePrediction>(model);
    var prediction = predictor.Predict(imageData);
    predictor.Dispose();
    System.IO.File.Delete(imagePath);  // throws a FileIO exception
    return prediction;
}

[giuseppe-terrasi]

Are there any updates on this issue?

[ganik]

I ll take a look, thx

[ganik]

@giuseppe-terrasi I am not able to repro this with the latest code from master branch. I checked that image file is loaded within using{ .... } statement before actual prediction happens (in \machinelearning\src\Microsoft.ML.ImageAnalytics\ImageLoader.cs : TryLoadDataIntoBuffer(..) method). Could you try your code with the latest ML.NET from master branch.

[giuseppe-terrasi]

@ganik Sorry for the delay. I created a test solution here.
I used both nuget versions 1.4.0 and 1.5.0-preview with the same result. I also tried to compile the source from master branch but I received a compilation error.

[giuseppe-terrasi]

Are there any updates on this issue? Due to it I have a lot of temporary images used by this code that I must delete manually after restarting the process. I can give more information if needed. Thanks.

[venkateshkrc]

This is not a solution to this issue but I faced the similar issue and ended up using ITransformer.Transform as an workaround for the prediction.

Using PredictionEngine is cleaner but ITransfomer does not seem to lock files.

[giuseppe-terrasi]

@ganik Still no updates?

[konabuta]

@ganik My customer also encounters this issue. Any update on this ?

[konabuta]

@ganik No updates on this ?

[ganik]

@giuseppe-terrasi @konabuta Hi, sorry for delay and thank you for repro solution. I was able to find the rootcause in machinelearning\src\Microsoft.ML.ImageAnalytics\ImageLoader.cs, line 238:
dst = new Bitmap(path) { Tag = path };
BitMap locks the file. There are various approaches how to handle this as per: https://stackoverflow.com/questions/4803935/free-file-locked-by-new-bitmapfilepath
I ll investigate various solutions and will submit a fix shortly. Thx.