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C# dispose unmanaged resource outside "using" and "try/finalize" block

I want a method to return an unmanaged resource and later in the program dispose of that resource. Does the following implementation do what I intend ?
class DocxManager
{
// DocX is the unmanaged resource
public Docx createDocX(string pathToFile)
{
return new DocX(pathToFile);
}
public void makeChangesAndSaveDocX(DocX wordDoc)
{
wordDoc.Save();
// IS THIS WAY THE UNMANAGED RESOURCE FREED CORRECTLY AND NO MEMORY LEAK ?
((IDisposable)wordDoc).Dispose();
}
}

First off all, you seem to be misunderstanding the concept of managed and unmanaged resources. wordDoc is not an unmanaged resource, its a managed resource which happens to either directly hold an unmanaged resource or acts as a wrapper around some other IDisposable object (you don't care wich of the two is true). Its important you are clear on this because otherwise you will not implement correctly the IDisposable pattern when you need to. Read this for a very instructive answer on the subject and a few chuckles courtesy of Eric Lippert.
Does the following implementation do what I intend ?
No, it does not and to make things worse, the contract of DocXManager is simply horrible (more on that later).
What hapens if wordDoc.Save() throws and exception because the file is being used by another process, or maybe you've run out of space in the hard drive, or you've lost connection, etc.?
If the thrown exception is not recoverable (it's not handled anywhere in your code or it is but you will terminate it ASAP) then it's not really an issue and the runtime will clean up everything behind you when the process is terminated. On the other hand, if the exception is handled (warn the user the file is in use, the directory is not available, etc.) and the process keeps running then you've just maybe leaked a resource.
How to avoid this? Use a try-finally block:
public void makeChangesAndSaveDocX(DocX wordDoc)
{
try
{
wordDoc.Save();
}
finally
{
((IDisposable)wordDoc).Dispose();
}
}
Now you are sure that Dispose() will be called in any recoverable scenario.
So, is this good enough? Well....not exactly. The problem here is that makeChangesAndSaveDocX's (that should be MakeChangesAndSaveDocX by the way) contract is unclear. Who is responsible of disposing wordDoc? MakeChangesAndSaveDocX or the caller? Why one or the other? How does the consumer know that he doesn't need to worry about wordDoc once he's called MakeChangesAndSaveDocX? Or how is he supposed to know he can't use wordDoc after calling the public method MakeChangesAndSaveDocX? Why does DocXManager assume that the consumer will not need to use wordDoc after calling MakeChangesAndSaveDocX? Yuck...this is a mess.
I'd recommend you reconsider your approach and do one of the following:
If the method signature MakeChangesAndSaveDocX(DocX wordDoc) makes sense (somebody else can own wordDoc), then do not dispose wordDoc in MakeChangesAndSaveDocX. Let the caller carry that burden, he should be responsible because the object belongs to him not to MakeChangesAndSaveDocX.
If on the other hand, it makes no sense that somebody else who is not DocXManager owns wordDoc then wordDoc should be part of the state of DocXManager and you should reconsider the implementation of DocXManager to something allong the following lines:
public class DocXManager: IDisposable
{
private readonly DocX docX;
private bool disposed;
public DocXManager(string filePath)
{
docX = new DocX(filePath);
}
public void MakeChangesAndSaveDocX()
{
if (disposed)
throw new ObjectDisposedException();
docX.Save();
}
public void FrobDocX(Frobber frobber)
{
if (disposed)
throw new ObjectDisposedException();
frobber.Frob(docX);
}
public void Dispose()
{
if (disposed)
return;
Dispose(true);
disposed = true;
GC.SupressFinalize(this);
}
public void Dispose(bool disposing)
{
if (disposing)
{
//we can sefely dispose managed resources here
((IDisposable)docX).Dispose();
}
//unsafe to clean up managed resources here, only clean up unmanaged resources if any.
}
~DocXManager()
{
Dispose(false);
}
}
Now you've got a clear contract; DocManagerX is responsible of disposing correctly of DocX and the consumer is responsible of disposing correctly of any instance of DocManagerX he might use. Once responsibilities are clear, its easier to reason about code correctness and who should do what.
You'd use the manager in the following way:
using (var manager = new DocXManager(path))
{
manager.FrobDoxX(frobber);
manager.MakeChangesAndSaveDocX();
} //manager is guaranteed to be disposed at this point (ignoring scenarios where finally blocks are not executed; StackOverflowException, OutOfMemoryException, etc.)

Delegate-parameterized method vs IDisposable implementation for temporary file operation

Narrowed question:
I need to implement reusable functionality that initializes a temporary file, runs some custom logic provided by the user, and then deletes the file. I can do this either through a static utility method that takes the user's logic as a delegate, or through a class that implements IDisposable to perform cleanup during Dispose. The two approaches would be used as follows:
// Delegate-parameterized method approach:
TempFile.Using(filePath =>
{
// use temporary file here
});
// IDisposable implementation approach:
using (var tempFile = new TempFile())
{
// use temporary file here
}
Which are the advantages and drawbacks to each approach? Which one should I use?
Original question:
I am developing some general-purpose functionalities that require a fixed “initialization – custom logic – clean-up” sequence. The clean-up must be performed as part of the same construct used for executing the operation; I don't want to confer the responsibility for calling a Cleanup or Close method to the user.
For example, I might want to provide functionality that automatically creates and deletes a temporary file. The simplest way to implement this is through a method that takes an Action<T> delegate:
public static void UsingTempFile(Action<string> action)
{
// initialization
string tempFilePath = Path.GetTempFileName();
try
{
action(tempFilePath);
}
finally
{
// clean-up
File.Delete(tempFilePath);
}
}
This could be used like so:
UsingTempFile(filePath =>
{
File.WriteAllText(filePath, "Hello world");
string text = File.ReadAllText(filePath);
});
However, this approach often requires me to implement four method overloads to support returned results and anonymous functions:
public static void UsingTempFile(Action<string> action) { /* ... */ }
public static TResult UsingTempFile<TResult>(Func<string, TResult> func) { /* ... */ }
public static async Task UsingTempFile(Func<string, Task> asyncAction) { /* ... */ }
public static async Task<TResult> UsingTempFile<TResult>(Func<string, Task<TResult>> asyncFunc) { /* ... */ }
The former three can implemented as simple wrappers that call the last overload. However, in a public API, they still need to be documented and unit-tested, substantially cluttering my codebase.
An alternative approach is to design an instantiatable class that implements IDisposable to represent the operation. This class would perform the initialization in its constructor, and the clean-up in its Dispose method. It could then be consumed like so:
using (var tempFile = new TempFile())
{
File.WriteAllText(tempFile.FilePath, "Hello world");
string text = File.ReadAllText(tempFile.FilePath);
}
The advantage of this approach is that the C# compiler automatically handles all my four cases ‒ the user can specify return and await keywords in the using block.
However, I often need to be able to throw exceptions from my clean-up logic – like IOException being thrown from File.Delete if the temporary file is still in use in the above example. The MSDN documentation for the Dispose Pattern states:
X AVOID throwing an exception from within Dispose(bool) except under critical situations where the containing process has been corrupted (leaks, inconsistent shared state, etc.).
Users expect that a call to Dispose will not raise an exception.
If Dispose could raise an exception, further finally-block cleanup logic will not execute. To work around this, the user would need to wrap every call to Dispose (within the finally block!) in a try block, which leads to very complex cleanup handlers.
A related question makes a stronger case about the downsides to throwing exceptions from finally blocks:
A first exception is thrown
A finally block is executed as a result of the first exception
The finally block calls a Dispose() method
The Dispose() method throws a second exception
[…] You lose information because .NET unceremoneously replaces the first exception with the second one. A catch block somewhere up the call stack will therefore never see the first exception. However, one is usually more interested in the first exception because that normally gives better clues as to why things started to go wrong.
This argument has merit – if the user's custom logic throws an exception, I would not want it to be hidden (and lost) by any exceptions thrown in the clean-up. There are solutions to this, such as Marc Gravell's wrapper for IDisposable objects (which swallows all Dispose exceptions), but this imparts more responsibility on the user. On the other hand, the .NET Framework Class Library itself seems to disregard this rule ‒ FileStream can throw exceptions from its Dispose method if it fails to flush the buffer's contents to disk.
Which of the two approaches (delegate-parameterized methods vs IDisposable) would be recommendable for these general-purpose implementations? Are there any implications apart from the ones mentioned above?
Update: This is an example of how delegate-parameterized methods can prevent main-logic exceptions from being swallowed:
public static void UsingTempFile(Action<string> action)
{
// initialization
string tempFilePath = Path.GetTempFileName();
bool isSuccess = false;
try
{
// main logic
action(tempFilePath);
isSuccess = true;
}
finally
{
try
{
// clean-up
File.Delete(tempFilePath);
}
catch
{
// only propagate exceptions from clean-up if there were
// no unhandled exceptions from the main logic
if (isSuccess)
throw;
}
}
}

Using the using-statement with an already instantiated object

I have a very simple logging mechanism in my application which periodically writes a line to a file (a logging library would be overkill for my needs) which looks something like this:
private string logfile = #"C:\whatever.log";
public void WriteLine(string line)
{
using(FileStream fs = File.Open(logfile, FileMode.Append))
{
// Log Stuff
}
}
So any time I call that method, a new FileStream is created and disposed after logging is finished. So I considered using an already instantiated object to prevent the continuous creation of new objects:
private string logfile = #"C:\whatever.log";
private FileStream myStream = File.Open(logfile, FileMode.Append);
public void WriteLine(string line)
{
using(myStream)
{
// Log Stuff
}
}
However, the MSDN reference discourages this (last example), due to scope issues.
What does one do in that case? Is the overhead in my first example negligible?

The using statement doesn't do anything else than calling the Dispose() method of the object.
So considering your second example, after the first call to the WriteLine(string) method the filestream is disposed. So any other call, after the first one, to this Method will result in an exception.
Using the File.AppendText() method like Chris had suggested in the comment would be a way to go. But keep in mind, that using this or any other File... method will also open a stream and close and dispose it afterwards.
It will just result in less code.

The second approach does also dispose the stream every time you call WriteLine since you are also using the using-statement. MSDN discourages from this approach because the variable myStream does still "exist" even if the object is disposed. So that is more error-prone.
If you often need to use this method you should cosider to use the using "outside" or use a try-catch-finally:
var myLogger = new MyLogger();
try
{
// here is your app which calls myLogger.WriteLine(...) often
}
catch(Exception ex)
{
// log it
}
finally
{
myLogger.Dispose(); // myLogger is your Log class, dispose should call myStream.Dispose();
}

The overhead might not be negligible, but that might be beside the point.
When you are using using, the creation, acquisition of resource and the disposing of the used resources is nicely scoped. You know where it starts, where it's used, and where it's finished.
If you go for the second scenario, you know where it starts (it's when the containing class is created), but after that, you have no platform-guaranteed way to control where it's used, and where (if at all) the resources are disposed.
You can do this yourself if this is critical code, and your containing class implements the IDisposable pattern properly, but this can be tricky and not for the faint of heart :)
However, you stated in the question "a logging library would be overkill for my needs", so I think you are fine with the minimal overhead. IMHO, you should be fine with one of the ready-made File methods, like File.AppendAllText:
public void WriteLine(string line)
{
//add an enter to the end
line += Environment.NewLine;
File.AppendAllText(logfile, line);
}
or File.AppendAllLines:
public void WriteLine(string line)
{
File.AppendAllLines(logfile, new []{line});
}

Why is the Destructor not being called?

I have a very interesting scenario where I would like a class to inform another entity it has been destroyed; however, its not doing what I want it too.
The Problem
The deconstructor, for some reason does not do what its supposed to do.
The Question
Why is the destructor not being invoked and make sure that it does do its necessary clean up.
The Code
So here we have the informer ~
class Connection
{
public const int Port = 50000;// Can be any range between 49152 and 65536
//Teh Constructor
public Boolean Connect()
{
//SetInformation
Information.Id = 545;
using (var WebServ = new ClientSDKSoapClient("ClientSDKSoap"))
{
ContinueConnection.WaitOne();
WebServ.ClientLogin(Information);
}
return true;
}
~Connection()
{
using (var WebServ = new ClientSDKSoapClient("ClientSDKSoap"))
{
WebServ.ClientLogout(Information);
}
}
}
Additional Information
I want the web service to record if the Connection Class is destroyed for any given reason.
When the client is connecting, it works perfectly. The Web Service records every method called from it. If I call ClientLogout explicitly, it will work.
I am aware I can implement IDisposable; however, this object is not intended to be used within the lifetime of one method. In fact, its intended for use for the entire duration of the program and the failure of this object basically results in the failure of the entire project. (Although I suppose main IS a method...)
I need to release a network connection; however, its not in this program, its in another program and unless ClientLogout is called, it won't be released.
My Research
Microsoft says that you should use the deconstructor for the release of unmanaged resources making an explicit reference to network connections. This ones got my quite stumped.

I think you should implement a Dispose pattern for your Connection class, rather than relying on an obscure deconstructor metaphor. This would be the "canonical" way to do it.
public class Connection : IDisposable // <== Inherit from IDisposable interface
{
public const int Port = 50000;// Can be any range between 49152 and 65536
private SomeType webserv; // Use whatever real type is appropriate here.
private Information information = new Information(); // or whatever
// This is a real constructor.
public Connection()
{
//SetInformation
information.Id = 545;
webServ = new ClientSDKSoapClient("ClientSDKSoap"))
webserv.ContinueConnection.WaitOne();
webServ.ClientLogin(information);
}
// Implement IDisposable interface
public void Dispose()
{
webServ.ClientLogout(information);
}
}
And then use it thusly
using (var connection = new Connection())
{
// Use the connection here.
}
The client will be logged out when you leave the using block.

Microsoft says that you should use the deconstructor for the release of unmanaged resources making an explicit reference to network connections. This ones got my quite stumped.
The docs here are misleading. It really just means you need a finalizer somewhere in your object inheritance chain, to ensure that any unmanaged resources are appropriately cleaned up. But you only need this finalizer once for the entire inheritance tree, at the level where the unmanaged resource is first allocated.
As an example, you do not need a destructor or finalizer if you build a class for a data access layer to wrap the SqlConnection type, because the core SqlConnection type already has one. What you should do, though, is implement IDisposable and write code to ensure prompt disposal, so the finalizer on your SqlConnection will be called sooner, rather than later. But if you were to build a whole new database engine that competes with Sql Server, MySql, Oracle, Access, and the like, and were implementing the ADO.Net provider for this new database engine, then would need to write a finalizer for your connection type, because none exists yet.
In this case, ClientSDKSoap type already has a destructor; you do not need to write another.

Cleanly shutting down a DLL's Static events in a host I don't control

Does the following psuedo code accomplish my goal of cleaning up after myself when my DLL is being hosted by code I don't control?
More specifically, how do I clean up my objects created in my static constructor?
Do I need to suppress Finalize in the Disposable?
Am I guaranteed that the compiler or something will call IDisposable even if the Host doesn't?
Psuedo code:
public class MyDLL : SomeHostICantControl, IDisposable
{
public SpinLock MyDictionarySpinlock = new Spinlock; // approximate syntax
public static Dictionary<string, string> MyDictionary = null;
public static Timer MyCleanUpTimer = null;
public static MyDLL()
{
// Set up Cache Here ... how do I dispose of it?
MyDictionary = new Dictionary<string, string>();
// remove old data from the dictionary, use spinlock to sync writes
// or use concurrent dictionary in .NET 4
MyCleanUpTimer = new Timer(); // run every hour
}
// many instances will be created and disposed of. I have no control when or how often
public void MyDll()
{
this.MyHostEvent += New Event Handler....
}
//.. some event handler code here
public void Dispose()
{
this.MyHostEvent -= Event Handler.;
// Do I need to suppressFinalize here?
}
//~MyDll()
//{
// Is this the right place to clean up after my constuctor?
//}
}

Answering your questions in order:
Static fields exist for the lifetime of the application, as such they are "cleaned up" as a result of the application exiting (memory is reclaimed, files are closed etc.). You don't appear to be doing anything that might require explicit action to be taken to clean-up (e.g. flushing buffered data in a StreamWriter to file), but perhaps there are details missing in your code snippet.
You need to suppress finalize in your Dispose() method if your class has a finalizer (yours appears not to as it's commented out), or if someone can derive from your class and may introduce unmanaged resources that may need cleaning up. The latter applies here as your class is not marked sealed, so you should suppress finalize in Dispose().
The runtime will not call Dispose(), however it will call the finalizer if one is present. Note however that as you class instances don't appear to be using any unmanaged resources, a finalizer should not be required.