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c#.netidisposablexmlreader
TOMMY WANG
TOMMY WANG

Reputation: 1402

Why is FileStream not closed by XmlReader

So I am using the FileStream inside XmlReader

using (XmlReader reader = XmlReader.Create(new FileStream(archivePath, FileMode.Open), readerSettings))
{
    reader.close()
}

However, the file feed into the XmlReader is still in the lock state after the using scope, weird, I thought the XmlReader is going to close the FileStream for me, is it not?

Thanks for help.

Upvotes: 10

Views: 11928

Answers (4)

Eric Patrick
Eric Patrick

Reputation: 2247

You should be able to control this through XmlReaderSettings.CloseInput.

readerSettings.CloseInput = true;
using (XmlReader reader = XmlReader.Create(new FileStream(archivePath, FileMode.Open), readerSettings))
{
    // do work with the reader
}

Or, more concisely if you don't care about other reader settings:

using (XmlReader reader = XmlReader.Create(new FileStream(archivePath, FileMode.Open), new XmlReaderSettings() { CloseInput = true }))
{
    // do work with the reader
}

Upvotes: 17

SunsetQuest
SunsetQuest

Reputation: 8827

A few years late but maybe this might help someone...

I tried Eric's method as it seemed like a good solution but I kept getting warning CA2202 when I ran VS code analysis on it.

Near the bottom of CA2202, Microsoft recommends to use the following:

(I slightly modified the it for "XmlReader".)

Stream stream = null;
try
{
    stream = new FileStream("file.txt", FileMode.Open);
    using (XmlReader reader = new XmlReader (stream))
    {
        stream = null;
        // Use the reader object...
    }
}
finally
{
    if(stream != null)
        stream.Dispose();
}

instead of...

using (Stream stream = new FileStream("file.txt", FileMode.Open))
{
    using (XmlReader reader = new XmlReader (stream))
    {
        // Use the reader object...
    }
}

It is much longer but at least it does not throw any warnings.

Upvotes: 0

Ed Swangren
Ed Swangren

Reputation: 124692

Have you tried this?

using(var stream = new FileStream(archivePath, FileMode.Open))
using(var reader = XmlReader.Create(stream, readerSettings))
{

}

I couldn't find anything in the documentation that explicitly stated that the XmlReader would call dispose on the underlying stream when it was disposed. Also, I always use it as shown above and I have never encountered a problem.

Browsing through reflector I also find no instances where it calls Dispose() on the stream when creating a XmlTextReaderImpl. The XmlTextReaderImpl does not implement Dispose() and its Close() method looks like this:

internal void Close(bool closeInput)
{
    if (this.parsingFunction != ParsingFunction.ReaderClosed)
    {
        while (this.InEntity)
        {
            this.PopParsingState();
        }
        this.ps.Close(closeInput);
        this.curNode = NodeData.None;
        this.parsingFunction = ParsingFunction.ReaderClosed;
        this.reportedEncoding = null;
        this.reportedBaseUri = string.Empty;
        this.readState = ReadState.Closed;
        this.fullAttrCleanup = false;
        this.ResetAttributes();
    }
}

Upvotes: 12

David
David

Reputation: 1153

You would need to keep track of the FileStream and the XmlReader. It's potentially dangerous for the XmlReader to close the underlying stream. In the case where the FileStream is used by multiple readers: if one of these readers were to close the stream this would cause the other readers to fail unexpectedly.

It's a bit of a pain since some stream readers and writers will close the underlying stream, while others don't. As a best practice I always close and dispose of the streams I open manually. This also helps mitigate some 'gotchas' with certain streams.
e.g. You need to dispose a GZipStream before calling .ToArray()

Upvotes: 1

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