I am using WPF.
After adding user controls dynamicaaly at runtime, How to Dispose that user control.
Because there is no Dispose Method for User Controls. i dont want to wait untill Garbage Collecter runs.
Even if you were able to dispose it, that wouldn't free memory. Dispose isn't about releasing memory - it's about releasing non-memory resources (e.g. GDI handles). I would assume that if the class doesn't implement IDisposable, it doesn't have any non-memory resources to release.
I think your design is flawed.
If you still have a reference to something then you shouldn't try to free the memory anyway.
Once something is actually no longer alive (no further references to it) it is effectively available memory in that, the next time you need some memory which cannot be supplied without a GC it will become free[1] and available.
Your design is not wasting memory, it is simply churning memory. This in itself may be problematic but it does not waste memory. If your design holds onto references to controls after they are no longer needed that wastes memory, but you cannot 'band-aid' over the problem by 'deleting' them. You need to tackle the root cause of passing these controls all about the place in a manner that makes their life cycle hard to control.
[1] barring finalizers which do not apply here
Is there a reason you don't want to wait for the GC? If you remove the control from it's parent so there's no references to it then the GC will eat it, there's no need to dispose of it manually.
Thanks Steve.
Firstly i add numerous UsrCtr Elements on my Application Frequently. so if they are't removed instanteously, Huge memory will be wasted.
Actually i am using ForEach Loop at several places to iterate all the elements on the Application (WinForm) , so this loop still show the UserCtrs (After removing the UserCtr as chld)
Further more i also pass the refrence of the UserCtrs to several other places in my project through the Custom Defined Events and Delegate. So if add it at one Place on Main Form, still there may be possiblity that Refrence for the User Control Exists some other Place in the Project.
Related
I know this may seem like a duplicate, but I think this specific case may be a bit different.
In my MVC application, I have a ViewModel containing a big List used to display a table similar to an Excel sheet. each MyComplexClass contains a list of MyComplexClass and a list of MyComplexColumn.
This makes a pretty big memory usage, but now I have a problem. I am supposed to write a method that cleans my big table, and load a different set of data into it. I could write something like:
MyViewModel.Lines = new List<MyComplexClass>();
MyViewModel.LoadNewSetOfData(SetOfData);
But, comming from a C background, explicitly losing my reference on the old List is not something I can do, and continue looking at my face in the mirror every morning.
I saw Here, Here, and Here, that I can set the reference to null, and then call
GC.Collect()
But I was told that I was not really best practice, especially because it may really affects performance, and because I have no way to know if the GC has disposed of this specific memory allocation.
Isn't there any way I can just call something like Free() and live on?
Thank you
Don't worry about it! Trying to "encourage" the garbage collector to reclaim memory isn't a great idea - just leave it to do its work in the background.
Just load your different set of data. If memory is getting low the GC will kick in to reclaim the memory without you having to do anything, and if there's plenty of memory available then you'll be able to load the new set without taking the hit of a garbage collection.
The short answer - don't worry about garbage collection. The only time I'd be concerned is if you're putting massive amounts of objects and data in a place where they might not get properly garbage collected at all. For example, you store tons of per-user data in ASP.NET session, and it sits there for a long time even though the user visits a few pages and leaves.
But as long as references to objects are released (as when they go out of scope) then garbage collection will do its job. It might not be perfect, but it's really, really good. The work and thought that went into developing good garbage collection in most cases probably exceeds the work that we put into developing the applications themselves.
Although we have the ability to trigger it, the design of the .NET framework deliberately allows us to focus on higher-level abstractions without having to worry about smaller details like when the memory is freed.
Is it instantaneous after the GC runs?
I was monitoring Memory (Available MBytes) using perfmon while running an application I'm working on. As I loaded files I could see the Available MBytes going down as expected, but as I closed them it didn't go back up so I'm wondering if I am not disposing correctly or if there is something else that affects this.
When a file is loaded:
the contents are stored in some objects
a new instance of a UserControl is created
a new TabPage is created
the UserControl is added to the TabPage
the TabPage is added to the TabControl
Reading on SO I saw that one of the most common things that can cause Memory Leaks is not unsubscribing from event handlers and so I made sure I did that in my UserControl's dispose method. I subscribe to the 'RemovingTab' event of the TabControl but the TabPages themselves have no attached handlers.
When closing a file, I remove stored instances of the objects and call dispose on both the UserControl and the TabPage. I tried running the CLR profiler (which I haven't had any experience with) and it said there was no GC runs.
Another common source of memory not being released is holding onto unmanaged resources, open files being one example.
The memory is available after the GC cleans up whatever is using it. Not every GC run results in memory being released. Any object that survives at least one GC run can end up living a long time because it's no longer in generation 0 - those could end up being around until the app actually needs more memory than is currently available to it. Large objects (larger than 85kb, as far as I remember) are stored on the large object heap which also isn't part of every GC run.
Your best bet is to look at what is actually holding the memory. Use the Visual Studio performance tools or try PerfView. Once you know what is actually holding the memory you'll be in a better position to figure out how to get it released.
Is it instantaneous after the GC runs?
No. As a matter of fact, depending on the memory pressure of your particular application, the GC might not free up any memory during the whole lifespan of your application.
Reading on SO I saw that one of the most common things that can cause Memory Leaks is not unsubscribing from event handlers and so I made sure I did that in my UserControl's dispose method.
Yes that is a common cause.
When closing a file, I remove stored instances of the objects and call dispose on both the UserControl and the TabPage. I tried running the CLR profiler (which I haven't had any experience with) and it said there was no GC runs.
The GC is very good at doing what it's supposed to do and it has been fined tuned to extremes. If it doesn't run its probably because it has decided that it doesn't need to run. Therefore, when the memory is freed up by the GC is up to the GC to decide and, if I'm not mistaken, is implementation defined, so it is not something you can rely upon.
And last but not least, the IDisposable pattern is not, by any means, a deterministic pattern for reclaiming memory; that is most definitely not the pattern's goal.
I have a C# WinForm User control made up of many child user controls such as MenuItem, ToolbarButton, ContextMenu, Splitter, Panel..etc..I open and close this user control many times in a ActiveX container. I see its it leaks memory every time it is open and close. I called GC.Collect in the dispose of this control and found that it leaks less memory now. but still it leaks.
I have also called the dispose on all other child controls MenuItem, ToolbarButton, ContextMenu, Splitter, Panel..etc in Dispose method of User Control but still i see that my User control is not GCed.
Please find the image from .Net profiler..you can copy the link of image in other tab of browser to see it large aaTrendControl is the name of my user control.
Find the image when I click on one child control instance in
Why MenuItem and ToolbarButton control are not releasing my UserControl even when I Dispose them..Is anything I am missing.
Simply calling GC.Collect will not release everything that went out of scope in one go. Garbage collection is allot more complicated. There is a concept of generations. Referring to objects that in turn refer to objects place them in different generations, and one call to GC.Collect will most likely only remove the last generations in one cycle. Calling it multiple times will also have little effect. If there's not much to do it may just ignore the call and return with "I'm done".
I recommend you read the excellent book Under the hood of .Net Memory Management. It's a freely downloadable PDF with allot of details on what's going on.
From your story, it is likely you are creating many "handles". Every control on a form has a so-called handle. These are native windows resources, that need to be "pinned" in order for windows to send messages to them (mouse-over, click etc...). Pinned objects are even more complicated because the GC cannot simply move them to another part of memory when defragmenting, so excessive allocation of controls can cause fragmentation problems. In the old days (before windows XP) there used to be a hard limit on the number of handles that a process would be allowed to allocate.
You may want to consider using GDI+ a little more to save out extra controls. For example, when creating excel-like grids, it is custom to draw the whole grid on one canvas, and only when the user clicks (or focuses) on a single cell, overlay it with a textbox or dropdown control in-place. Creating separate controls for each cell would have an enormous overhead, even on a modern computer.
It's good practice to re-use controls instead of disposing them and recreating them. Reusing controls will have a huge positive impact on performance. This because of the fact that visual controls require a context switch between your process and the OS in order to acquire a handle. Unfortunately I don't know of a good book on windows forms. I learned most of the details from my old Delphi 2 books, almost two decades ago. I might be outdated on some details, but the essential basic concepts in WinForms have not changed since then. Even when you work with .Net, an old book on the native Windows API's should help you get an idea on what's going on under the hood.
.Net will take care of the memory management saving you quite some headache, but fragmentation can cause problems, which can be overcome by reusing visual objects instead of disposing them. If you really need to call GC.Collect in your code, it usually implies you are doing something else wrong (exceptions exist though).
I've been reading a lot about this since I've been asked to fix a C# application that has memory leaking problems, but I haven't found an answer for these 2 issues:
Consider the following code:
private static ArrayList list = new ArrayList();
public void Function()
{
list.add(object1);
list.add(object2);
//didn't call clear() prior to reusing list
list = new ArrayList();
}
Since the list wasn't cleared before creating a new one, will this generate some sort of garbage that won't be released after the static list itself is disposed?
The second issue is regarding Form.Dispose(). I see that a lot of controls available on designer view (i.e. labels, picture boxes) require disposing. It's seems as though calling Dispose() on a Form causes all of these types of controls to be disposed also (correct me if I'm wrong), which is odd since the designer adds an overriden void Dispose(bool disposing) method which does no such thing. I'm assuming that this happens at the void Dispose(bool disposing) method of the base Form class.
The problem with the above is that it is not very clear to me what I need to do to ensure that all of the Form's resources are disposed correctly. I do not understand how the Form knows which objects it needs to dispose. For example, if in my form I have a field which is a custom IDisposable object, will the Form know that it needs disposing? Or should I add the code necessary to release the object myself?
Also, if I do need to add the code to dispose certain objects, then how do I deal with the fact that the designer has already overriden the void Dispose(bool disposing) method? Should I edit the designer generated code or is there a cleaner way to do this?
I hope that this wasn't to confusing, it's a bit hard to explain. Thanks
No, that's not a leak. When the garbage collector goes searching for object references, it won't find a reference to the original ArrayList anymore. You replaced it. So it will automatically destroy that original ArrayList object, as well as all of its elements if they are not referenced anywhere either.
The Form class knows how to dispose itself, as well as all the controls that are child windows on that form. This happens when the user closes the form, the WM_CLOSE message that Windows sends triggers this code. The Form.Controls collection helps it find the reference to all child controls so it can dispose them too.
However, this will not happen if you remove controls from the form yourself. Now it is up to you to call Dispose() on them. Particularly the Controls.Clear() method is dangerous. What is unusual about it is that this causes a permanent leak, the controls you remove are kept alive by the 'parking window'. Which keeps the window handle alive so you can move them elsewhere, on another container window for example. If you don't actually move them, they'll stay hosted on that parking window forever. No other classes in the framework quite behave this way.
This leak is easy to diagnose with Taskmgr.exe, Processes tab. View + Select Columns and tick USER Objects. If this steadily goes up while your program runs then you're leaking controls.
What is the scope of your Static arraylist. Looks to me that it has a form scope. If it is, it will not be disposed since static objects are always considered rooted and has an application life time. In my experience, statics always take more memory and get promoted to gen 2 because of this fact. If you have any doubts, take a .net memory profiler and check it out. You can also take memory dumps and analyze it using windbg to figure out the real cause of the leak.
In many memory-management frameworks, garbage-collected and otherwise, freeing up memory within an application does not generally cause the application to release that memory, but instead record the fact that the memory should be available for future requests. Part of the idea behind garbage collection is that when user code asks for memory and the application knows that it has at least that much immediately available, neither the code nor the application will care about whether any memory not needed for that request is "allocated" or "free". When the last reachable reference to an object is destroyed or becomes unreachable, the object effectively ceases to exist right then and there, but there's generally not much purpose in trying to reclaim memory formerly used by non-existent objects until such reclamation is either required to fulfill an allocation request, or the "memory freed per time spent" ratio is as good as its likely to get.
Note that for the system to reclaim the memory associated with an object, it is absolutely imperative that no reference of any sort exist to that object. If there exist any reachable weak references to an object which is not otherwise reachable, the garbage-collector must invalidate all such references (so they no longer identify the object) before the space used by the object can be reclaimed. If an otherwise-unreachable object has a registered finalizer, the system must put the object on a queue of things needing immediate finalization (thus making it ineligible for reclamation) and unregister the finalizer.
Weak references and the references used for finalization are both invalidated automatically by the GC when all other references to an object are abandoned, and thus do not cause memory leaks. There's another kind of reference, however, which can cause nasty leaks: event subscriptions from publishers that outlive subscribers. If object A subscribes to an event from object B, object A cannot be garbage-collected unless either (1) it unsubscribes from the event, or (2) B itself becomes eligible for garbage-collection. I find myself puzzled at why Microsoft didn't include some means of automatic event unsubscription, but they didn't.
I use a for loop to generate some controls. Each control presents a special visualisation. I can not use controls like ListBox or somethink like that. I must use my approach. The generated controls are hosted in a Canvas. After a while, some controls are not longer needed. Some controls must be removed. I can manually remove a controls via
c.Children.Remove( ... );
this line. How do I determine that the controls was really collected from be garbage collection? Maybe the control already exists in the memory ... . How do I ensure this?
The problem is that I generate data in tons!
Thanks in advance! :-)
So if you call to Destroy the control, and you haven't maintained any other references to the control in memory (like in a hashtable of controls or something), then the GC will collect it.
Don't try and force the .NET GC to do something fancy, let it do its work in its own time as the library authors designed it. If you Destroy it, it will be gone, in due time.
Lastly, if you're concerned that it's still consuming memory, it will be time to start profiling your code, like for instance with RedGate Ants.
Depending on the control that you're using maybe you need to call Control.Dispose() to free all resources. Be careful is you are using unmanaged resources (Learn more)
I think this is not your case.
Then the garbage collector will collect the object for you.
Also, this article about how Garbage Collector works could be very interesting:
http://www.codeproject.com/KB/dotnet/Memory_Leak_Detection.aspx
You don't really need to. That's the sense of garbage collection: as soon as there are too many dead objects, garbage collection jumps in and cleans them out. Or doesn't clean: the GC knows better what and when to remove.
As long as nothing holds a reference to a control, the garbage collector will get rid of it and you have nothing to worry about. Usually, removing a control from the collection that contains it all you need to do.
But you must be careful with event handlers. If object A subscribes to an event that object B raises, object B holds a reference to object A. If your controls subscribe to, say, Canvas.IsEnabledChanged, you can remove them from the Canvas, but the Canvas will still hold a reference to them so that it can notify them when IsEnabled changes, and they won't be garbage-collected. This is the most common cause of "memory leaks" in .NET applications. (They're not really memory leaks, but they might as well be.)
if you're sure the objects arent referenced anywhere anymore, you can force a call to the garbage collector with gc.Collect()