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 ) 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);
}