Things that you didn’t know

I am working on a some sort of file cache system lately and I’ve encountered a bizarre error. When a certain file representing an image had to be deleted it wouldn’t let it – an IOException was thrown stating:

The process cannot access the file '[FILEPATH]' because it is being used by another process.

The odd thing is that I’ve used this file only for retrieve images from and I had no idea why would it be locked. Eventually I’ve traced the lock down to this line:

Image result = Image.FromFile(path);

Would you say that the line above would lock a file? I wouldn’t. But it does for some obscure reason. Thus switching to Image.FromStream did the trick:

using (FileStream stream = File.OpenRead(path))
{
    return Image.FromStream(stream);
}

It is more lines but it works as expected.

IMPORTANT UPDATE: The workaround described above only seems to work - it crashes randomly. By reading documentation (who does that anyway? - thanks Dario for the hint Smile) it states that the stream has to open for the lifetime of the Image. Ouch. So here is the second workaround that works for sure - I copy the data to a MemoryStream and create image from there. It is even more lines but this time it has to work (there is a Stream.CopyTo method in forthcomming .net 4.0).

using (FileStream stream = File.OpenRead(path))
{
    MemoryStream imageDataStream = new MemoryStream(Convert.ToInt32(stream.Length));
    byte[] buffer = new byte[4096];
    int read;
    while ((read = stream.Read(buffer, 0, buffer.Length)) != 0)
    {
        imageDataStream.Write(buffer, 0, read);
    }
    imageDataStream.Position = 0;
    return Image.FromStream(imageDataStream);
}

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