In the unmanaged languages like C++ I can delete object using delete operator. But .NET platform is managed, so only the garbage collector can delete object from memory. We can only remove all references to the object and Garbage Collector will collect it sometime. But I want to perform instant delete of object.
Is there a way delete object using C++ library? The main idea:
Create C++ library
Define method DeleteUnsafe(void* pointer) that uses mscoree.dll to delete object
Refer to the C++ library from .NET using DllImport attribute
Is it possible to perform second step? Or use some another way to achieve my goal? What the start point?
Is it possible to perform without corrupting CLR? For example, GC will try collect already deleted object. How we can remove the object from GC queue?
Not too sure about the why you want to do this, but I'll assume you have a reason.
What comes to mind would be forcing garbage collection, but here's a quote from MS:
"It is possible to force garbage collection by calling Collect, but
most of the time, this should be avoided because it may create
performance issues. "
(you can have a look here for more: https://stackoverflow.com/a/233647/1698987.
Other than that, if you really need that fine control, maybe c# ain't the answer?
hmm ... have a look at this msdn page. Seems that calling GC.Collect method assuming that you know what you're doing isn't that bad after all... :)
Related
I need to dispose of an object so it can release everything it owns, but it doesn't implement the IDisposable so I can't use it in a using block. How can I make the garbage collector collect it?
You can force a collection with GC.Collect(). Be very careful using this, since a full collection can take some time. The best-practice is to just let the GC determine when the best time to collect is.
Does the object contain unmanaged resources but does not implement IDisposable? If so, it's a bug.
If it doesn't, it shouldn't matter if it gets released right away, the garbage collector should do the right thing.
If it "owns" anything other than memory, you need to fix the object to use IDisposable. If it's not an object you control this is something worth picking a different vendor over, because it speaks to the core of how well your vendor really understands .Net.
If it does just own memory, even a lot of it, all you have to do is make sure the object goes out of scope. Don't call GC.Collect() — it's one of those things that if you have to ask, you shouldn't do it.
You can't perform garbage collection on a single object. You could request a garbage collection by calling GC.Collect() but this will effect all objects subject to cleanup. It is also highly discouraged as it can have a negative effect on the performance of later collections.
Also, calling Dispose on an object does not clean up it's memory. It only allows the object to remove references to unmanaged resources. For example, calling Dispose on a StreamWriter closes the stream and releases the Windows file handle. The memory for the object on the managed heap does not get reclaimed until a subsequent garbage collection.
Chris Sells also discussed this on .NET Rocks. I think it was during his first appearance but the subject might have been revisited in later interviews.
http://www.dotnetrocks.com/default.aspx?showNum=10
This article by Francesco Balena is also a good reference:
When and How to Use Dispose and Finalize in C#
http://www.devx.com/dotnet/Article/33167/0/page/1
Garbage collection in .NET is non deterministic, meaning you can't really control when it happens. You can suggest, but that doesn't mean it will listen.
Tells us a little bit more about the object and why you want to do this. We can make some suggestions based off of that. Code always helps. And depending on the object, there might be a Close method or something similar. Maybe the useage is to call that. If there is no Close or Dispose type of method, you probably don't want to rely on that object, as you will probably get memory leaks if in fact it does contain resourses which will need to be released.
If the object goes out of scope and it have no external references it will be collected rather fast (likely on the next collection).
BEWARE: of f ra gm enta tion in many cases, GC.Collect() or some IDisposal is not very helpful, especially for large objects (LOH is for objects ~80kb+, performs no compaction and is subject to high levels of fragmentation for many common use cases) which will then lead to out of memory (OOM) issues even with potentially hundreds of MB free. As time marches on, things get bigger, though perhaps not this size (80 something kb) for LOH relegated objects, high degrees of parallelism exasperates this issue due simply due to more objects in less time (and likely varying in size) being instantiated/released.
Array’s are the usual suspects for this problem (it’s also often hard to identify due to non-specific exceptions and assertions from the runtime, something like “high % of large object heap fragmentation” would be swell), the prognosis for code suffering from this problem is to implement an aggressive re-use strategy.
A class in Systems.Collections.Concurrent.ObjectPool from the parallel extensions beta1 samples helps (unfortunately there is not a simple ubiquitous pattern which I have seen, like maybe some attached property/extension methods?), it is simple enough to drop in or re-implement for most projects, you assign a generator Func<> and use Get/Put helper methods to re-use your previous object’s and forgo usual garbage collection. It is usually sufficient to focus on array’s and not the individual array elements.
It would be nice if .NET 4 updated all of the .ToArray() methods everywhere to include .ToArray(T target).
Getting the hang of using SOS/windbg (.loadby sos mscoreei for CLRv4) to analyze this class of issue can help. Thinking about it, the current garbage collection system is more like garbage re-cycling (using the same physical memory again), ObjectPool is analogous to garbage re-using. If anybody remembers the 3 R’s, reducing your memory use is a good idea too, for performance sakes ;)
I'm sure this has been asked before and I just don't know the right terms to search for. In a C# program I am working on I have an List that keeps track of Objects. Those objects can also be displayed on the screen via references by other objects.
Sometimes after an object is removed from the list it is still temporarily available to those other objects (as it should be)... After those objects are done however I want to make sure the object is 100% gone and not staying in memory still being referenced by a forgotten object... How can I do this?
To be clear, this doesn't need to happen as part of the shipped program, only for debugging.
You normally can't. The GC is meant to take care of memory management behind the scenes, and does it's job very specifically and by means best not trifled with. In particular, other parts of your code may keep a reference to the item you want removed, which SHOULD prevent its collection. such is the nature of memory managed languages such as C#.
That being said, however, there are a few ways to check for when an object is disposed. The easiest to to create a simple destructor and breakpoint it, allowing you to "see" whenever an object is collected.
~MyClass()
{ // Breakpoint here
}
The other way is to make a static list of WeakReferences to your objects, which each object subscribes to when it's created. Make sure to keep that other list, however, as a weak reference is specifically designed to allow garbage collection, allowing you to track an object to its destruction. The other list is necessary to keep the objects alive. Also note that in .NET 4.5, there is a generic version of WeakReference. EDIT: This is definitely the solution I recommend after seeing the updates to your question. You can also quickly query which objects are still being refernced via Linq
var leftoverObjects = WeakCache
.Select(wr => wr.Target)
.OfType<MyObject>() // Only if you're not using that Generic Weak Reference
.Except(ObjectList); // filters away objects in the List
Be warned the above query creates a result which has strong references, so once run, it'll keep those objects in memory as long as the result is referenced.
If you have some sort of unmanaged memory backing your object, that's exactly what the IDisposable interface is designed for.
UPDATE: finally, if you MUST do so, you can Force the GC to Collect. This is often heavily advised against, as you start to warp the Generations that help optimize the GC in the first place.
I guess you need this for testing purpose. In such case I would recommend to use memory profiler such as ANTS Memory Profiler or JetBrains dotTrace. You can find more complete list of profilers here
There is no easy way to look for an object reference "backwards", basically you would need to use reflection to loop through all objects and structs that exist in the application and check all references. You just have to make sure that all code that uses the reference really removes it when they are done.
One way to check if there seems to be any live references (but not where they are) is to keep a list of weak references to the objects that you don't use any more. The weak references will not keep the objects from being collected, but you can use them to check if the objects have been collected or not.
As there is no guarantee that an object should be collected within any certain time, you can never know for sure if it's an actual reference that keeps an object alive, but the longer the objects survive, the more likely it is that you have a reference to it somewhere.
Sorry for being confused, at C++ I know to return local variable's reference or pointers can cause bad_reference exception. I am not sure how it is in C# ?
e.g
List<StringBuilder> logs = new List<StringBuilder>();
void function(string log)
{
StringBuilder sb = new StringBuilder();
logs.Add(sb);
}
at this function a local object is created and stored in a list, is that bad or must be done in another way. I am really sorry for asking this, but I am confused after coding C++ for 2 months.
Thanks.
Your C# code doesn't return an object reference so it doesn't match your concern. It is however a problem that doesn't exist in C#. The CLR doesn't let you create objects on the stack, only the heap. And the garbage collector makes sure that object references stay valid.
In C#, the garbage collector manages all the (managed) objects you create. It will not delete one unless there are no longer any references to it.
So that code is perfectly valid. logs keeps a reference to the StringBuilder. The garbage collector knows this, so it will not clean it up even after the context in which it was originally created goes out of scope.
In C# object lifecycle is managed for you by the CLR; compared to C++ where you have to match each new with a delete.
However in C# you can't do
void fun()
{
SomeObject sb(10);
logs.Add(sb);
}
i.e. allocating on the stack you have to use new - so in this respect both C# and C++ work similarly - except when it comes to releasing / freeing the object reference.
It is still possible to leak memory in C# - but it's harder than in C++.
There's nothing wrong with the code you've written. This is mostly because C#, like any .NET language, is a "managed" language that does a lot of memory management for you. To get the same effect in C++ you would need to explicitly use some third-party library.
To clear up some of the basics for you:
In C#, you rarely deal with "pointers" or "references" directly. You can deal with pointers, if you need to, but that is "unsafe" code and you really avoid that kind of thing unless you know what you're doing. In the few cases where you do deal with references (e.g. ref or out parameters) the language hides all the details from you and lets you treat them as normal variables.
Instead, objects in C# are defined as instances of reference types; whenever you use an instance of a reference type, it is similar to using a pointer except that you don't have to worry about the details. You create new instances of references types in C# in the same way that you create new instances of objects in C++, using the new operator, which allocates memory, runs constructors, etc. In your code sample, both StringBuilder and List<StringBuilder> are reference types.
The key aspect of managed languages that is important here is the automatic garbage collection. At runtime, the .NET Framework "knows" which objects you have created, because you're always creating them from it's own internally-managed heap (no direct malloc or anything like that in C#). It also "knows" when an object has gone completely out of scope -- when there are no more references to it anywhere in your program. Once that happens, the runtime is able to free the memory whenever it wants to, typically when it starts to run low on free memory, and you never have to do it. In fact, there is no way in C# to explicitly destroy a managed object (though you do have to clean up unmanaged resources if you use them).
In your example, the runtime knows that you've created a StringBuilder and put it into a List<>; it will keep track of that object, and as long as it's in the List<> it will stick around. Once you either remove it from the List<>, or the List<> itself goes away, the runtime will automatically clean up the StringBuilder for you.
Scenario
Lets say that I've decided I really need to call GC.Collect();
What do I need to do to ensure that an object is prepared to be garbage collected appropriately before I actually call this method?
Would assigning null to all properties of the object be enough? Or just assigning null to the object itself?
If you really need to know why.....
I have a distributed application in WCF that sends a DataContract over the wire every few seconds, containing 8 Dictionaries as DataMembers.
This is a lot of data and when it comes into the Client-side interface, a whole new DataContract object is created and the memory usage of the application is growing so big that I'm getting OutOfMemory Exceptions.
Thanks
EDIT
Thanks for all the comments and answers, it seems that everyone shares the same opinion.
What I cannot understand is how I can possibly dispose correctly because the connection is open constantly.
Once I've copied the data over from the incoming object, I don't need the object anymore, so would simply implementing IDisposable on that DataContract object be enough?
My original problem is here - Distributed OutOfMemory Exceptions
As long as nothing else can see the object it is already eligible for collection; nothing more is required. The key point here is to ensure that nothing else is watching it (or at least, nothing with a longer lifetime):
is it in a field somewhere?
is it in a variable in a method that is incomplete? (an infinite loop or iterator block, perhaps)
is it in a collection somewhere?
has it subscribed to some event?
it is captured in a closure (lambda / anon-method) that is still alive?
I genuinely doubt that GC.Collect() is the answer here; if it was eligible it would have already been collected. If it isn't elgible, calling GC.Collect() certainly won't help and quite possibly will make things worse (by tying up CPU when nothing useful can be collected).
You don't generally need to do anything.
If the object is no longer referenced then it's a candidate for collection. (And, conversely, if the object is still referenced then it's not a candidate for collection, however you "prepare" it.)
You need to clean up any unmanaged resources like database connections etc.
Typically by implementing IDisposable and call Dispose.
If you have a finalizer you should call GC.SuppressFinilize.
The rest is cleaned up by the garbage collector.
Edit:
And, oh, naturally you need to release all references to your object.
But, and here is this big but. Unless you have a very very special case you don't need to call GC.Collect. You probably forgets to release some resources or references, and GC.Collect won't help you with that. Make sure you call Dispose on everything Disposable (preferably with the using-pattern).
You should probably pick up a memory profiler like Ants memory profiler and look where all your memory has gone.
If you have no more direct reference to an object, and you're running out of memory, GC should do this automatically. Do make sure you call .Dispose() on your datacontext.
Calling GC.Collect will hardly ever prevent you from getting OutOfMemory exceptions, because .NET will call GC.Collect itself when it is unable to create a new object due to OOM. There is only one scenario where I can think of and that is when you have unreferenced objects that are registered in the finalizable queue. When these objects reference many other objects it can cause a OOM. The solution to this problem is actually not to call GC.Collect but to ensure that those objects are disposed correctly (and implement the dispose pattern correctly when you created those objects).
Using GC.Collect in general
Since you are trying to get rid of a very large collection, it's totally valid to use GC.Collect(). From the Microsoft docs:
... since your application knows more about its behavior than the runtime does, you could help matters by explicitly forcing some collections. For example, it might make sense for your application to force a full collection of all generations after the user saves his data file.
"Preparing" your objects
From the excellent Performance Considerations for Run-Time Technologies in the .NET Framework (from MSDN):
If you keep a pointer to a resource around, the GC has no way of knowing if you intend to use it in the future. What this means is that all of the rules you've used in native code for explicitly freeing objects still apply, but most of the time the GC will handle everything for you.
So, to ensure it's ready for GC, Make sure that you have no references to the objects you wish to collect (e.g. in collections, events, etc...). Setting the variable to null will mean it's ready for collection before the variable goes out of scope.
Also any object which implements IDisposable should have it's Dispose() method called to clean up unmanaged resources.
Before you use GC.Collect
Since it looks like your application is a server, using the Server GC may resolve your issue. It will likely run more often and be more performant in a multi-processor scenario.
The server GC is designed for maximum throughput, and scales with very high performance.
See the Choosing Which Garbage Collector to Use within Performance Considerations for Run-Time Technologies in the .NET Framework (from MSDN):
One of my friend told me that dynamic method is the only way if you want to at run time construct code that can be garbage collected.
One question in my mind that how garbage collector garbage the object which generated using reflection?
An object constructed using reflection will be garbage collected like any other type of object, for example when it leaves the scope of a method if it's a method variable.
Garbage collection will collect any .NET objects. It doesn't differ wether they are created using reflection or not.
how should an object created by reflection be different than one created normally?
you have an instance variable of this object... the runtime exactly knows what type of object it is, and also does the GC.
only the way the object is created is different. the object should be exactly the same as one created with new MyObject()
There is more complexity than this.
For example, search for Tess (good MS employee) blog about xml serializer leaking memory.
There are ways to fix this in code pattern. Anyway, this xml serializer memory leak problem won't be fixed by GC. In fact, these types of dynamically generated dll only get deleted when the parent app is unloaded (IIS worker process that hosts web service that use xml serializer).
Bottom line: even for .Net project, don't rely on GC for all cases. There are leaks that need work-around code/code pattern fix.
This bug is still in 3.5 I think.
More link:
http://plainoldstan.blogspot.com/2011/04/wcf-memory-leak-with.html
read the Tess link an other link inside this:
Are there still known memory leaks with XMLSerialization in .Net 3.5?
Any piece of code that runs under the control of CLR is managed code and CLR governs and decides for garbage collection.
there are ways in which you can coltrol the Garbage collection but unless it is really required let CLR decide.