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CA2202, how to solve this case
(12 answers)
Closed 8 years ago.
CA2000 and CA2202 warnings have recently been the bane of my existence. What am I doing wrong here? I basically get a FileStream using File.Open and then pass it into a function that may return a new stream or may return the same stream. I then perform some more actions on my stream and then in my finally block I dispose the stream I was using if it was different.
I get two CA warnings. 2000 for fileStream in the using block and 2202 for changedStream in the finally block. What gives?
using (Stream fileStream = File.Open(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
Stream changedStream = null;
try
{
changedStream = someCondition ? fileStream : DoSomeActionThatMayReturnNewStream(fileStream);
DoSomeMoreStuffWithStream(changedStream);
}
finally
{
if (changedStream != null && changedStream != fileStream)
{
changedStream.Dispose();
}
}
}
Under what cases, if any, will DoSomeActionThatMayReturnNewStream dispose of the passed-in stream? If when it creates a new stream it disposes of the passed-in one (which would generally be expected), the Dispose triggered by the using block will be redundant.
It appears as though the behavior of your code might be correct if DoSomeActionThatMayReturnNewStream never disposes of the passed-in stream, but FxCop has no way of analyzing its complex and unorthodox pattern of object ownership. I would suggest that it would be better to do something like
Stream inputFile = null;
try
{
inputFile = File.Open(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
DoSomeActionThatMayReturnNewStream(ref inputFile);
DoSomeMoreStuffWithStream(inputFile);
}
finally
{
if (inputFile != null)
inputFile.Dispose();
}
The DoSomeActionThatMayReturnNewStream should dispose of the old stream if it's going to open a new one. It should null the variable immediately before closing the old stream and and assign it immediately upon opening the new one. That will ensure that if an exception occurs during the method, the old stream will get disposed if and only if it hasn't been disposed before, and the new stream will get disposed if its constructor completed, even if the DoSomeActionThatMayReturnNewStream threw an exception after that [if that method calls Dispose on the new stream in case an exception gets thrown, it should null out the variable in such case].
What's wrong with the following:
using (var fileStream = System.IO.File.Open(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (var changedStream = someCondition ? fileStream : DoSomeActionThatMayReturnNewStream(fileStream))
{
DoSomeMoreStuffWithStream(changedStream);
}
}
Related
why in fs2 object throw error ?? i already have written a FileShare.ReadWrite in fs object
FileStream fs = new FileStream("hello.txt",FileMode.OpenOrCreate,FileAccess.ReadWrite,FileShare.ReadWrite);
mama();
Console.ReadKey();
}
static void mama()
{
FileStream fs2 = new FileStream("hello.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
fs2.Read(new byte[3], 0, 3);
}
can any one tell me why this error ?
error = The process cannot access the file 'C:\Users\iP\documents\visual studio 2015\Projects\ConsoleApplication32\ConsoleApplication32\bin\Debug\hello.txt' because it is being used by another process.
You're getting that error because you're passing FileShare.None to the second call. If you change that to FileShare.ReadWrite to match the first call, you won't have that problem.
The reason for this is because the FileStream constructor calls CreateFileW underneath, and if you take a look at the documentation for that function, it states:
You cannot request a sharing mode that conflicts with the access mode
that is specified in an existing request that has an open handle.
CreateFile would fail and the GetLastError function would return
ERROR_SHARING_VIOLATION.
You already have an open handle from the first request using FileAccess.ReadWrite as the access mode, which conflicts with FileShare.None in the second call.
Because your code never closes the file and has an open handle to it
If you can, always use the using statement, it will flush and close the file
using(var fs = new FileStream(...))
{
// do stuff here
} // this is where the file gets flushed and closed
If 2 methods are working on the same file, pass the FileStream in
static void mama(FileStream fs )
{
fs .Read(new byte[3], 0, 3);
}
I have read the MSDN page on this: https://msdn.microsoft.com/en-us/library/ms182334.aspx
And also this SO answer: https://stackoverflow.com/a/32554589/2257227
But the following code still generates 2 CA2202 warnings for me:
FileStream fileStream = null;
BufferedStream bufferedStream = null;
try
{
fileStream = File.Open(...);
bufferedStream = new BufferedStream(fileStream);
using (StreamReader streamReader = new StreamReader(bufferedStream))
{
...
}
}
finally
{
if (bufferedStream != null)
{
bufferedStream.Dispose();
}
if (fileStream != null)
{
fileStream.Dispose();
}
}
The "bufferedStream.Dispose()" line still gives the following two warnings:
Severity Code Description Project File Line Suppression State
Warning CA2202 Object 'bufferedStream' can be disposed more than once in method 'Loader.UpdateIndex()'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 930 Loader C:\Users\user\Loader\Loader.cs 930 Active
and
Severity Code Description Project File Line Suppression State
Warning CA2202 Object 'fileStream' can be disposed more than once in method 'Loader.UpdateIndex()'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 930, 935 Loader C:\Users\user\Loader\Loader.cs 930 Active
Presumably this is because fileStream could be disposed of more than once? But how can bufferedStream be disposed of more than once?
Edit: I've marked #Damien_The_Unbeliever's answer as correct. You can actually trim it down as well, because as was mentioned somewhere below, you don't need the bufferedReader variable. Here's what I ended up with. It's kinda ugly, but it works:
FileStream fileStream = null;
try
{
fileStream = File.Open("iaushdiuh", FileMode.Open);
fileStream = null;
using (StreamReader streamReader = new StreamReader(fileStream))
{
streamReader.ReadLine();
}
}
finally
{
if (fileStream != null)
{
fileStream.Dispose();
}
}
If you don't use the underlying streams after you've "passed ownership" of these objects to other objects, you can silence the warning like this:
FileStream fileStream = null;
BufferedStream bufferedStream = null;
try
{
fileStream = File.Open(...);
bufferedStream = new BufferedStream(fileStream);
fileStream = null;
using (StreamReader streamReader = new StreamReader(bufferedStream))
{
bufferedStream = null;
...
}
}
finally
{
if (bufferedStream != null)
{
bufferedStream.Dispose();
}
if (fileStream != null)
{
fileStream.Dispose();
}
}
You'll want the assignments to null to occur immediately following the constructor call that "takes ownership" of the disposable object. In this way, you ensure that if the constructor throws, you dispose the inner object and if the constructor succeeds then it is then going to arrange for disposal to occur.
in my WPF application code i got the following Warnings:
CA2202 Do not dispose objects multiple times Object 'fs' can be
disposed more than once in method
'MainWindow.TestResults_Click(object, RoutedEventArgs)'. To avoid
generating a System.ObjectDisposedException you should not call
Dispose more than one time on an object. : Lines:
429 yesMonitor MainWindow.xaml.cs 429
for code:
FileStream fs = new FileStream(System.AppDomain.CurrentDomain.BaseDirectory + "TestResult.htm", FileMode.Create);
using (fs)
{
using (StreamWriter w = new StreamWriter(fs, Encoding.UTF8))
{
w.WriteLine(GetTestResultsHtml());
}
}
what should be the reason for these warning?
Nested using statements can cause violations of the CA2202 warning. If the IDisposable resource of the nested inner using statement contains the resource of the outer using statement, the Dispose method of the nested resource releases the contained resource. When this situation occurs, the Dispose method of the outer using statement attempts to dispose its resource for a second time.
In the following example, a Stream object that is created in an outer using statement is released at the end of the inner using statement in the Dispose method of the StreamWriter object that contains the stream object. At the end of the outer using statement, the stream object is released a second time. The second release is a violation of CA2202.
using (Stream stream = new FileStream("file.txt", FileMode.OpenOrCreate))
{
using (StreamWriter writer = new StreamWriter(stream))
{
// Use the writer object...
}
}
To resolve this issue, use a try/finally block instead of the outer using statement. In the finally block, make sure that the stream resource is not null.
Stream stream = null;
try
{
stream = new FileStream("file.txt", FileMode.OpenOrCreate);
using (StreamWriter writer = new StreamWriter(stream))
{
stream = null;
// Use the writer object...
}
}
finally
{
if(stream != null)
stream.Dispose();
}
Personally in this case I would use:
public StreamWriter(
string path,
bool append
)
Initializes a new instance of the StreamWriter class for the specified
file by using the default encoding and buffer size. If the file
exists, it can be either overwritten or appended to. If the file does
not exist, this constructor creates a new file.
But there is NO good solution, see CA2202, how to solve this case
I'm using : boito = Serializer.DeSerializeObject("XOPC.xml"); with try catch.
so here is method :
public static ObjectToSerialize DeSerializeObject(string filename)
{
ObjectToSerialize objectToSerialize;
Stream stream = File.Open(filename, FileMode.Open);
BinaryFormatter bFormatter = new BinaryFormatter();
objectToSerialize = (ObjectToSerialize)bFormatter.Deserialize(stream);
stream.Close();
return objectToSerialize;
}
I had changed structure and it's failing to DeSerialize this file but on next step when I'm trying to serialize it again I'm getting error : "This file is using by another process" and I can't access it.
So how to stop using file after error in deserialization ?
You're not closing the stream if an exception is thrown. Use a using statement:
using (Stream stream = File.Open(filename, FileMode.Open))
{
BinaryFormatter bFormatter = new BinaryFormatter();
return (ObjectToSerialize) bFormatter.Deserialize(stream);
}
This is equivalent to disposing of the stream in a finally block.
This isn't just about deserialization - you should (almost1) always use using statements for unmanaged resources. Any explicit call to Close or Dispose (outside a Dispose implementation merely releasing composed resources) is suspicious.
1 Very occasionally you want to leave a resource open on success, but close it if something else fails. This is rare and awkward.
When I run code analysis on the following chunk of code I get this message:
Object 'stream' can be disposed more than once in method 'upload.Page_Load(object, EventArgs)'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.
using(var stream = File.Open(newFilename, FileMode.CreateNew))
using(var reader = new BinaryReader(file.InputStream))
using(var writer = new BinaryWriter(stream))
{
var chunk = new byte[ChunkSize];
Int32 count;
while((count = reader.Read(chunk, 0, ChunkSize)) > 0)
{
writer.Write(chunk, 0, count);
}
}
I don't understand why it might be called twice, and how to fix it to eliminate the error. Any help?
I struggled with this problem and found the example here to be very helpful. I'll post the code for a quick view:
using (Stream stream = new FileStream("file.txt", FileMode.OpenOrCreate))
{
using (StreamWriter writer = new StreamWriter(stream))
{
// Use the writer object...
}
}
Replace the outer using statement with a try/finally making sure to BOTH null the stream after using it in StreamWriter AND check to make sure it is not null in the finally before disposing.
Stream stream = null;
try
{
stream = new FileStream("file.txt", FileMode.OpenOrCreate);
using (StreamWriter writer = new StreamWriter(stream))
{
stream = null;
// Use the writer object...
}
}
finally
{
if(stream != null)
stream.Dispose();
}
Doing this cleared up my errors.
To illustrate, let's edit your code
using(var stream = File.Open(newFilename, FileMode.CreateNew))
{
using(var reader = new BinaryReader(file.InputStream))
{
using(var writer = new BinaryWriter(stream))
{
var chunk = new byte[ChunkSize];
Int32 count;
while((count = reader.Read(chunk, 0, ChunkSize)) > 0)
{
writer.Write(chunk, 0, count);
}
} // here we dispose of writer, which disposes of stream
} // here we dispose of reader
} // here we dispose a stream, which was already disposed of by writer
To avoid this, just create the writer directly
using(var reader = new BinaryReader(file.InputStream))
{
using(var writer = new BinaryWriter( File.Open(newFilename, FileMode.CreateNew)))
{
var chunk = new byte[ChunkSize];
Int32 count;
while((count = reader.Read(chunk, 0, ChunkSize)) > 0)
{
writer.Write(chunk, 0, count);
}
} // here we dispose of writer, which disposes of its inner stream
} // here we dispose of reader
edit: to take into account what Eric Lippert is saying, there could indeed be a moment when the stream is only released by the finalizer if BinaryWriter throws an exception. According to the BinaryWriter code, that could occur in three cases
If (output Is Nothing) Then
Throw New ArgumentNullException("output")
End If
If (encoding Is Nothing) Then
Throw New ArgumentNullException("encoding")
End If
If Not output.CanWrite Then
Throw New ArgumentException(Environment.GetResourceString("Argument_StreamNotWritable"))
End If
if you didn't specify an output, ie if stream is null. That shouldn't be a problem since a null stream means no resources to dispose of :)
if you didn't specify an encoding. since we don't use the constructor form where the encoding is specified, there should be no problem here either (i didn't look into the encoding contructor too much, but an invalid codepage can throw)
if you don't pass a writable stream. That should be caught quite quickly during development...
Anyway, good point, hence the edit :)
The BinaryReader/BinaryWriter will dispose the underlying stream for you when it disposes. You don't need to do it explicitly.
To fix it you can remove the using around the Stream itself.
A proper implementation of Dispose is explicitly required not to care if it's been called more than once on the same object. While multiple calls to Dispose are sometimes indicative of logic problems or code which could be better written, the only way I would improve the original posted code would be to convince Microsoft to add an option to BinaryReader and BinaryWriter instructing them not to dispose their passed-in stream (and then use that option). Otherwise, the code required to ensure the file gets closed even if the reader or writer throws in its constructor would be sufficiently ugly that simply letting the file get disposed more than once would seem cleaner.
Your writer will dispose your stream, always.
Suppress CA2202 whenever you are sure that the object in question handles multiple Dispose calls correctly and that your control flow is impeccably readable. BCL objects generally implement Dispose correctly. Streams are famous for that.
But don't necessarily trust third party or your own streams if you don't have unit tests probing that scenario yet. An API which returns a Stream may be returning a fragile subclass.