Dispose of object more than one time error. CA2202. Is there a better way?

4
votes

How can I ensure the following code is disposing of all objects in a better fashion? Currently, Code Analysis is telling me

Error 45 CA2202 : Microsoft.Usage : Object 'ns' can be disposed more than once in method 'CPCommunicator.GetResults(string)'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 64, 65

NetworkStream ns = null;
StreamWriter requestStream = null;
TextReader responseStream = null;

var results = new StringBuilder();

try
{
    ns = new NetworkStream(CreateConnection(), true);
    requestStream = new StreamWriter(ns);
    requestStream.Flush();
    responseStream = new StreamReader(ns);

    requestStream.Write(reportData);
    requestStream.Flush();
    while (responseStream.Peek() != -1)
    {
        var currentLine = responseStream.ReadLine();
        results.Append(currentLine);
        results.Append("\n");
    }
}
finally
{
    if (requestStream != null) requestStream.Close();
    if (responseStream != null) responseStream.Close();
    if (cpNetworkStream != null) cpNetworkStream.Close();
}

Since both requestStream and responseStream use ns, they both dispose of ns so in order to satisfy the code analysis warning, I have to comment out the last two close methods in the finally block. But do I really want to do this?????

2
c#dispose
Although the recommendation is definitely good practice, the documentation for Dispose states that "if an object's Dispose method is called more than once, the object must ignore all calls after the first one. The object must not throw an exception if its Dispose method is called multiple times". msdn.microsoft.com/en-us/library/… - LukeH
@LukeH: The recommendation could be considered "good practice" for exactly one reason: Ideally, an object is disposed at the end of its useful life, and disposing it a second time could imply or even cause some confusion about its real vs intended lifetime. But as you said, correct implementation of IDisposable requires that Dispose be idempotent. - cHao

2 Answers

4
votes

Yes, imho you really should only call it once.

Alternatively you could use the using syntax on ns, which makes the whole situation even clearer.

using (ns = new NetworkStream(CreateConnection(), true)) {
   ...
}
2
votes

I would refactor your code to be like this:

using (NetworkStream ns = new NetworkStream(CreateConnection(), true))
using (StreamWriter requestStream = new StreamWriter(ns))
using (TextReader responseStream = new StreamReader(ns))
{

    var results = new StringBuilder();

    requestStream.Flush();

    requestStream.Write(reportData);
    requestStream.Flush();
    while (responseStream.Peek() != -1)
    {
        var currentLine = responseStream.ReadLine();
        results.Append(currentLine);
        results.Append("\n");
    }
}