how can you implement the Dispose method after using "using" on a MemoryStream object in a class that implements IDisposable?
public class ControlToByte :IDisposable
{
public static byte[] GetByte(object control)
{
using (System.IO.MemoryStream memoryStream = new System.IO.MemoryStream())
{ //do something here }
public void Dispose()
{
//how do you dispose of memorystream object?
}
You don't have to implement IDispose, nor do you have to call Dispose explicitly. The using block will ensure that, after completion, the MemoryStream will be disposed. using blocks actually work like try/finally blocks. Something like:
{
System.IO.MemoryStream memoryStream = null;
try
{
memoryStream = new System.IO.MemoryStream();
//....your code
}
finally
{
if (memoryStream != null) //this check may be optmized away
memoryStream.Dispose();
}
}
using C#
The using statement ensures that Dispose is called even if an
exception occurs while you are calling methods on the object. You
can achieve the same result by putting the object inside a try block
and then calling Dispose in a finally block; in fact, this is how
the using statement is translated by the compiler.
In your current code, you are implementing IDisposable on your class ControlToByte, This would be useful if you want to dispose resourses in ControlToByte. As illustrated, you don't need to implement IDisposable for your class.
Related
I have an issue with the following code. I create a memory stream in the GetDB function and the return value is used in a using block. For some unknown reason if I dump my objects I see that the MemoryStream is still around at the end of the Main method. This cause me a massive leak. Any idea how I can clean this buffer ?
I have actually checked that the Dispose method has been called on the MemoryStream but the object seems to stay around, I have used the diagnostic tools of Visual Studio 2017 for this task.
class Program
{
static void Main(string[] args)
{
List<CsvProduct> products;
using (var s = GetDb())
{
products = Utf8Json.JsonSerializer.Deserialize<List<CsvProduct>>(s).ToList();
}
}
public static Stream GetDb()
{
var filepath = Path.Combine("c:/users/tom/Downloads", "productdb.zip");
using (var archive = ZipFile.OpenRead(filepath))
{
var data = archive.Entries.Single(e => e.FullName == "productdb.json");
using (var s = data.Open())
{
var ms = new MemoryStream();
s.CopyTo(ms);
ms.Seek(0, SeekOrigin.Begin);
return (Stream)ms;
}
}
}
}
For some unknown reason if I dump my objects I see that the MemoryStream is still around at the end of the Main method.
That isn't particuarly abnormal; GC happens separately.
This cause me a massive leak.
That isn't a leak, it is just memory usage.
Any idea how I can clean this buffer ?
I would probably just not use a MemoryStream, instead returning something that wraps the live uncompressing stream (from s = data.Open()). The problem here, though, is that you can't just return s - as archive would still be disposed upon leaving the method. So if I needed to solve this, I would create a custom Stream that wraps an inner stream and which disposes a second object when disposed, i.e.
class MyStream : Stream {
private readonly Stream _source;
private readonly IDisposable _parent;
public MyStream(Stream, IDisposable) {...assign...}
// not shown: Implement all Stream methods via `_source` proxy
public override void Dispose()
{
_source.Dispose();
_parent.Dispose();
}
}
then have:
public static Stream GetDb()
{
var filepath = Path.Combine("c:/users/tom/Downloads", "productdb.zip");
var archive = ZipFile.OpenRead(filepath);
var data = archive.Entries.Single(e => e.FullName == "productdb.json");
var s = data.Open();
return new MyStream(s, archive);
}
(could be improved slightly to make sure that archive is disposed if an exception happens before we return with success)
I wrote a piece of code. I want to make sure that I am Disposing an Object in right way.
I have a Disposable Class like this
Which is used to read some data from unmanaged resource.
class MyFileReader : IDisposable
{
private readonly FileStream _stream;
public MyFileReader(FileStream stream)
{
_stream = stream;
}
public void Dispose()
{
_stream.Dispose();
}
}
Currently in my program I Dispose objects like this.
using (FileStream stream = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read))
{
using (MyFileReader reader = new MyFileReader(stream))
{
//...
}
}
This seems ok to me. later I have noticed That Classes are passed by reference so maybe if I dispose one of them there is no need to dispose the other one.
My question is Can i Do Something like this?
using (FileStream stream = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read))
{
MyFileReader reader = new MyFileReader(stream);
// Remove IDisposable from MyFileReader and stream will close after using.
}
Or this one?
FileStream stream = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read);
// stream will close after using.
using (MyFileReader reader = new MyFileReader(stream))
{
//...
}
Yes, you can write code like that.
But, no, you should not do that.
Your class looks like on of XxxxReader classes that by convention own the stream they read from. As result your MyFileReader class is expected to dispose the inner stream. You also normally expected to dispose each and every disposable object when you know that such object's lifetime is over.
Note that sometimes it lead to multiple Dispose calls on some objects (which should be expected by implementations of IDisposable). While it may sometimes lead to Code Analysis warning it is better than missing Dispose calls if one routinely tries to "optimize" number of calls to Dispose by skipping some.
Alternative approach is to expose method that reads content which by convention is not expected to take ownership of stream/reader like:
using(stream....)
{
var result = MyFileReader.ReadFrom(stream);
}
If MyFileReader is accessing some unmanaged resource and you need the Disponse method to be called explicitly after this code block, then you have to stick with your current implementation.
In the second implementation, the Dispose method will not be called for the MyFileReader object. (until you probably call it in the destructor which you don't know when that would be called)
If you do not like the nested using, then you can probably go with the second alternative and in the Dispose() method implementation of MyFileReader class, explicitly dispose the Stream. If this stream is only use by MyFileReader, then this is a good practice to have MyFileReader manage its lifecycle and dispose it.
Many framework stream-wrapping classes have constructor overloads with leaveOpen parameter that controls stream disposing behavior.
Examples include StreamReader, BinaryReader, GZipStream.
There is also property approach, SharpZipLib example:
using (var zip = new ZipInputStream(stream) { IsStreamOwner = false }) { ... }
Code is:
using (MemoryStream memorystream = new MemoryStream(bytes))
{
using (BinaryWriter writer = new BinaryWriter(memorystream))
{
writer.Write((double)100.0);
}
return memorystream.ToArray();
}
Isn't the above code appropriate to properly dispose of both object?
Is the code analysis at all useful? Other than garbage information about variables names and namespaces it seems to complain about a lot of things that are not reality. I am really thinking that maybe it is useful and I am just missing the point.
OKAY to address concerns whether the MemoryStream is disposed of or not (its not) here is an example where the VS code analysis gives me the exact same warning. Clearly nothing is getting disposed of here
public class MyClass : IDisposable
{
public void DoSomethingElse()
{
}
#region IDisposable Members
public void Dispose()
{
throw new NotImplementedException();
}
#endregion
}
public class MyOtherClass : IDisposable
{
public MyOtherClass(MyClass mc)
{
}
public void DoSomething() { }
}
public void Foo()
{
using (MyClass mc = new MyClass())
{
using (MyOtherClass otherclass = new MyOtherClass(mc))
{
otherclass.DoSomething();
}
mc.DoSomethingElse();
}
}
On "If the stream were disposed then how can I call memorystream.ToArray()" part of the question:
MemeoryStream.Dispose does not release internal buffer. The only thing that it does is blocking all Stream methods (like Read) by throwing "Object Disposed" exception. I.e. following code is perfectly valid (usually similar code accessing lower level storage can be written for other other Stream objects that manage some sort of storage):
MemoryStream memoryStream = new MemoryStream();
using (memoryStream)
{
// write something to the stream
}
// Note memoryStream.Write will fail here with an exception,
// only calls to get storage (ToArray and GetBuffer) make sense at this point.
var data = memoryStream.ToArray();
BinaryWriter does not dispose the MemoryStream. YOU NEED TO DISPOSE OF IT. Get the results of .ToArray in a variable, then dispose the MemoryStream, then return the result. Or use a try/finally to dispose of the MemoryStream.
If I were to guess I would say that the logic of the analysis rule is identifying a possiblity that goes someting like this:
"You are passing a disposable object into the constructor of another disposable object (thus semantically implying a transfer of ownership). If ownership is truly being trasnsferred to the second object, it's likely that it will dispose of the object passed to its constructor in its own Dispose method but you're disposing of it as well."
Your second example proves that it is not actually analysing whether or not the second object takes ownership of and disposes the first, but rather this rule is saying this pattern has some semantic ambiguity, as the code responsible for disposal of the first object is no longer clear.
The dispose pattern has all of the inherent pitfalls of alloc/free and new/delete as only one class should own and thus control the lifetime of a disposable instance.
All pure conjecture of course but that's how I'd read it.
MemoryStream wraps a managed buffer that will be garbage collected at some point in the future regardless of whether its disposed of.
The IDisposable implementation is part of the Stream contract. It closes the stream preventing you from using the Read and Write methods but you are still permitted to access the underlying bytes. (Preventing calls to ToArray would probably make it difficult to use with StreamWriters.) A Stream implementation that does use unmanaged resources like a FileStream would release the file handle when it is disposed of.
The code analysis is noting that both you and the StreamWriter are calling Dispose on the same object and warning about it. This is pretty meaningless for a MemoryStream but might be dangerous with some other IDisposable implementations.
You appear to be confusing the IDisposable interface with garbage collection. Calling Dispose does not release managed objects, it just gives your class the opportunity to release unmanaged resources in a deterministic manner.
I think BinaryWriter.Dispose() will call its underlying MemoryStream's .Dispose(), and then your using will re-dispose it.
At least I think that's what will happen. I haven't opened the source for BinaryWriter to verify, but I was always under the impression it closed and disposed its underlying stream.
Edit:
This is the source for the classes. You can see where your memory stream is being disposed:
BinaryStream:
public BinaryWriter(Stream output) : this(output, new UTF8Encoding(false, true))
{
}
public BinaryWriter(Stream output, Encoding encoding)
{
if (output==null)
throw new ArgumentNullException("output");
if (encoding==null)
throw new ArgumentNullException("encoding");
if (!output.CanWrite)
throw new ArgumentException(Environment.GetResourceString("Argument_StreamNotWritable"));
Contract.EndContractBlock();
OutStream = output;
_buffer = new byte[16];
_encoding = encoding;
_encoder = _encoding.GetEncoder();
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
OutStream.Close();
}
MemoryStream:
public class MemoryStream : Stream
{
....
}
Stream
public virtual void Close()
{
Dispose(true);
GC.SuppressFinalize(this);
}
To answer one of your further questions, "why can you still call .ToArray() if MemoryStream has been disposed", well, this test passes just fine:
[TestMethod]
public void TestDispose()
{
var m = new MemoryStream();
m.WriteByte(120);
m.Dispose();
var a = m.ToArray();
Assert.AreEqual(1, a.Length);
}
So the .ToArray() method is still accessible after dispose.
The bytes are still available. MemoryStream dispose just sets some flags internally that prevent you from further modifying the stream:
protected override void Dispose(bool disposing)
{
try {
if (disposing) {
_isOpen = false;
_writable = false;
_expandable = false;
// Don't set buffer to null - allow GetBuffer & ToArray to work.
}
}
finally {
// Call base.Close() to cleanup async IO resources
base.Dispose(disposing);
}
}
In fact, note that the source has the comment in it:
// Don't set buffer to null - allow GetBuffer & ToArray to work.
so that really answers that question :)
I have a class which reads data from one file stream and writes to another. I am concerned about closing the streams after the processing has finished in closeFiles().
How would you handle the possibility that the dispose of one stream may throw an exception stopping the dispose of the other stream from being called.?
Should I be calling close and dispose on the streams or just one?
What happens if I catch any errors from the stream disposes and then continue with moving and deleting of the files as shown in lastOperation()?
In a perfect world I'd like to use a using statement in a c++ style initialisation list but I'm pretty sure that's not possible in c#.
EDIT : thanks for the quick responses guys. So what I should be doing is deriving from IDisposable and then change the constructor and add the two disposing methods like this?:
~FileProcessor()
{
Dispose(true);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
private void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
sw.Flush();
}
closeFiles();
disposed = true;
}
}
This is basically what I'm doing:
class FileProcessor
{
private string in_filename;
private string out_filename;
private StreamReader sr;
private StreamWriter sw;
bool filesOpen = false;
public FileProcessor(string filename)
{
in_filename = filename;
out_filename = filename + ".out";
openFiles();
}
~FileProcessor()
{
closeFiles();
}
private void openFiles()
{
sr = new StreamReader(in_filename);
sw = new StreamWriter(out_filename);
filesOpen = true;
}
private void closeFiles()
{
if (filesOpen)
{
sr.Close();
sw.Close();
sr.Dispose();
sw.Dispose();
filesOpen = false;
}
}
/* various functions to read, process and write to the files */
public void lastOperation()
{
closeFiles();
File.Delete( in_filename );
Directory.Move(out_filename, outdir + out_filename);
}
}
Your FileProcessor class should not have a destructor. It is of no use but it is expensive.
It should have a Dispose() (and implement the IDisposable interface) to call closeFiles().
And like #marcelo answered, Stream.Dispose() should not throw. You can rely on this for BCL classes.
But you should check each Reader/Writer for null, in case the first one opened but the second one failed:
if (sr != null) sr.Dispose();
if (sw != null) sw.Dispose();
Your filesOpen can't cover both.
I think it is a good practise to have your class implements IDisposable interface if you are using IDisposable object inside it.
Then, you should make sure that, in your Dispose() implementation, don't throw exceptions. If every object you dispose makes this guarantee, your client will be safe.
Dispose methods should never throw exceptions. There's even a code analysis tool warning for this.
In C#, using does exist. The object provided to the using statement must implement the IDisposable interface. This interface provides the Dispose method, which should release the object's resources.
If your StreamReader and StreamWriter implement IDisposable, you can put them in a using block, and they will be disposed of cleanly when you have finished with them.
using(var sr = new StreamReader(in_filename)) {
// Perform reader actions
}
// Reader will now be disposed.
I have a class DocumentGenerator which wraps a MemoryStream. So I have implemented IDisposable on the class.
I can't see how/where I can possibly dispose it though.
This is my current code, which performs a file download in MVC:
using (DocumentGenerator dg = DocumentGenerator.OpenTemplate(path))
{
/* some document manipulation with the
DocumentGenerator goes here ...*/
return File(dg.GetDocumentStream(), "text/plain", filename);
}
This errors as the stream is closed/disposed before the controller has finished with it. How can I make sure my resources are properly disposed in this situation?
EDIT: My implementation of IDisposable at the moment just disposes the MemoryStream. I know it's not a proper implementation, I just used it as a test. Is there something different I could do here to make it work?
public void Dispose()
{
_ms.Dispose();
_ms = null;
}
You don't need to dispose the stream. It will be disposed by the FileStreamResult.WriteFile method. Code excerpt from this class:
public FileStreamResult(Stream fileStream, string contentType) : base(contentType)
{
if (fileStream == null)
{
throw new ArgumentNullException("fileStream");
}
this.FileStream = fileStream;
}
protected override void WriteFile(HttpResponseBase response)
{
Stream outputStream = response.OutputStream;
using (this.FileStream)
{
byte[] buffer = new byte[0x1000];
while (true)
{
int count = this.FileStream.Read(buffer, 0, 0x1000);
if (count == 0)
{
return;
}
outputStream.Write(buffer, 0, count);
}
}
}
Notice the using. When you call File(dg.GetDocumentStream(), "text/plain", filename) from your controller this invokes the constructor which stores the stream into a public property which is disposed during the rendering.
Conclusion: you don't need to worry about disposing the stream obtain with dg.GetDocumentStream().
Just to add to what Darin has said, it's important to note this concept:
public Stream GetDownloadFile(...)
{
using (var stream = new MemoryStream()) {
return stream;
}
}
public Stream GetDownloadFile(...)
{
using (var generator = DocumentGenerator.OpenTemplate(path))
{
// Document manipulation.
return File(generator.GetDocumentStream(), "text/plain", filename);
}
}
Regardless of how you are using it in your method, the using block ensures that Dispose is always called, this is important when you consider to use the result of the using block as a return statement, it won't stop it from being disposed....