Does anybody know of a way to automatically find any variable, where the type implements IDisposable but the using construct is not used?
ie. a way to check for potentially unreleased unmanaged resources?
Also, is it possible to see the number and types of resource held by a running application?
There's a code analysis rule for this:
http://msdn.microsoft.com/en-us/library/ms182289%28VS.100%29.aspx
This can be run from VS 2010 Premium or Ultimate or separately with FxCop:
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=917023f6-d5b7-41bb-bbc0-411a7d66cf3c
Another thing I've seen done is to capture a stack trace when an IDisposable object is constructed and then if the finalize is hit (meaning Dispose() was not called) log an error with the constructed stack trace. This is expensive so you may only want to do it in development, or only start collecting stack traces the second time your app runs into this problem (if you run into it once, you're most likely going to run into it many times within a single app execution). This method works for IDisposable instances that are longer lived (not just local variables). Of course it also only works for custom IDisposable objects since it requires custom code in the constructor/dispose/finalizer.
VS 2010 code analyzer's and FxCop? (not sure) Reliability Rules will do a pretty good job on detecting if there exists execution paths in the analyized code where objects implementing IDisposable are going out of scope without calling Dispsoe() (it is overeager and will in many ocasions detect false positives).
This will of course not enforce the using construct as a correctly implemented try-finally block will pass the test (both are obviously equivalent under the hood, so I'm not sure if thats an issue).
EDIT: FX Cop does not support this warning. Its availabe since VS 2005 code analyzer.
Related
I am trying to figure out the cause of a (possible) memory leak in a complex C# based application. As I cannot debug the problem at runtime due to the system becoming very slow and unstable because of the high CPU and memory usage of the application, I created a dump (dmp) file of the application via the task manager at runtime and then opened that dump for further analysis in my local Visual Studio 2022 instance. When I now try to view the threads of the application at the point of time when the dump was created, it only shows me the call stack until where something async is executed. Everything that happens inside this async execution seems impossible to access. In the call stack it just says that it is waiting for an async process and I should double click or press enter to show async call stacks. However, this doesn't seem to do anything. Am I missing something, or how can I see what is happening inside the async process?
The typical approach to find memory leaks would be to create two or more memory snapshots/dumps and compare them with a memory debugger to see if there is some type of object that seem to only increase in count. I'm not sure stack traces would provide all that much value when trying to find memory leaks.
I have mostly used dotMemory but have no affiliation. I would expect most competent tools to have equivalent functionality, but terminology might be different.
There should be a comparison view where you should be able to sort object by either delta count or delta bytes . This often provides a good indication on what objects are leaking.
Once you have a candidate type you should be able to inspect an instance of that type and some way to view a retention graph where you can view the graph of objects keeping your instance alive. If you see anything suspicious, you should review the code and see if there is some possibility for leaks.
Common reasons are unregistered event handlers. If a object registers an event handler it should also ensure it is unregistered. If it is done in the constructor you should implement IDisposable and unregister in the dispose method, and ensure the object is always disposed. Possibly with a finalizer that only runs for undisposed objects, that logs, or otherwise alerts you, that the object was not disposed.
I've had this problem several times and until now not found a satisfying solution for it (restarting the computer is quite annoying if it takes 15 min to do so...):
When programming something with files, you have to use filestreams. The problem with them is (at least in C#) that they need to release the file again before you can access it from another place. As this is of course a good idea most of the time, it happened to me a few times that I forgot to release the file in the process of programming and debugging or the program crashed before the stream could be closed.
Is there any way to find and kill those streams using windows features or something like that? Problems like that occured in C# as well as in C++ (or C, I am not sure anymore).
From the answers I read, that this should not occur when the stream is handled properly. But what if I was to dumb to handle it right and the stream is not closed properly (because of whatever reason)? Is there a way to fix this while the PC is running?
This should not be a problem.
When your application is running normally, you use a using block to ensure that unmanaged resources like these are properly released. This is necessary for any object that implements the IDisposable interface.
If that fails, the operating system will jump in and save your bacon. The OS automatically releases any file handles that a process had open when it terminates, so even if your application crashes, there is no issue.
Anything that implements the IDisposable interface (which includes Streams) should always be either enclosed in a using block or be a member of a class which in turn implements IDisposable itself (and the new Dispose() method will also call the member's Dispose() method). There ought to be a compiler warning for this, imo.
Do this, and your file locks will be released properly.
I need to find automatically all code that not disposed properly.
Is it possible to check via reflection that my type N is used inside using statement (Dispose is called)?
No. The closest you could come is to add a finalizer - possibly conditionally so that it's only included for debug builds - which checks whether or not you've been disposed and logs the problem otherwise. (You'd probably want to keep the stack trace on construction in this case, in order to blame the right code.)
Bear in mind that adding finalizers will cause garbage to stick around for longer - although in your Dispose call you could suppress finalization, so correct code wouldn't have a significant penalty, other than generating the stack trace on construction...
Now that's all assuming you want to do things at execution time. There are various static analysis tools (such as the code analysis built into Visual Studio) which will tell you at build time if it looks like you haven't disposed of everything appropriately.
I have a ASP.NET C# singleton (scoped to a session through HttpContext.Current.Session) which receives messages from code (warnings, errors, exceptions etc.). The messages are related to code problems, mainly used while debugging, not during production.
I wrote the custom destructor for this object so that its contents are written/appended as a file on a disk.
I wanted to ask two things related to this situation:
a] Is is a good idea to open a file and write to it during object destructor? The concurrency IO access is handled through static lock.
b] When is the destructor called for session scoped objects? Is it only when the session is expired on the server?
I also recommend using some existing logging package. If you do decide to do this yourself, and just to bare in mind for the future:
a) No it's not a good idea. You shouldn't access managed resources in the finalizer (destructor), so if you have some log strings in memory for example, it's bad practice to access them (or the list they are contained in) as they may have already been finalized themselves at this point.
I don't want to repeat the recommended pattern, so see https://stackoverflow.com/a/1943856/2586804
You'll see there is only one place you should access managed during Dispose and this is if it is called by user code and not be the GC. So this should help you come to the conclusion that to achieve this, you must call .Dispose() yourself (or by using a using) as when (and if) the GC does it, it cannot access the managed members that contain the log lines.
b) Don't know, but it doesn't matter as you cannot use finalizer for this purpose anyway.
The bottom line is you can't rely on GC to run code for you. It's bad practice because you don't know when it's going to happen, plus any reference to the object anywhere, now or in the future will prevent the object being collected and introduce a bug.
You also shouldn't get c# Finalizers/Destructors to run code because that's not what they are for, they are for freeing unmanaged resources so that the machine doesn't run out. And note, it's a rare occurrence to use them in C# because most peoples day-to-day work is all with managed objects.
Instead explicitly tell the object to write it's logs, a method called Flush would be a good name. Or just let it write one line at a time. This would be the usual behaviour.
To accomplish this implement IDisposable and then wrap instances of your logger in a using block which will guarantee to call the dispose method on your logger.
I am thinking about adding a diagnostics mode build into an app I am writing to count method usage and execution time, similar to what many code profilers like dotTrace do.
I'm having some trouble finding resources through google on how to accomplish this though; obviously it is possible, but can anyone point me to some resources on how I can implement something like method call counts in .NET?
The Code Project article Creating a Custom .NET Profiler describes the process of creating a profiler using the CLR profiler hooks.
This involves creating a COM object that implements the ICorProfilerCallback2 interface and then using environment variables to indicate to the CLR that we wish to profile by using this class:
When the CLR begins a process, it looks for two environment variables:
COR_ENABLE_PROFILING: This environment variable is set to either 1 or 0. 1 indicates that the CLR should use a profiler. 0 (or the non-existence of this environment variable) indicates that it should not use a profiler.
COR_PROFILER: Now that we've told the CLR that we want to profile, we have to tell it which profiler to use. Because profilers are implemented as COM objects, this environment variable will be set to the GUID of the coclass that implements the ICorProfilerCallback2 interface.
Perhaps I am being too simple here, but my solution to this would be logging. Using entlib or log4net and log debug level messages. Then you can just write a little script/program to analyse the log file and give you the method count. There might even be other log diagnostic tools.
Unless you need rich visualization or real time complex relationship mapping etc. Would you need a profiler? For method count and execution time, wouldn't a log file suffice? Once you are in production or don't care about instrumentation you turn your logging level up and forget about those debug messages.