Best Practices No 5 - Detecting .NET Application Memory Leaks

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Best Practices No 5: Detecting .NET application memory leaks

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CPOL 28 Sep 2009 78,607 322 times

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By Shivprasad koirala | 20 Aug 2010 | Unedited contribution.NET1.0 .NET1.1 .NET2.0 VS2005 C#1.0 C#2.0 .NET3.0 C#3.0 .NET3.5 VS2008

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In this article we are going to detect the .NET application memory leaks.65

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Best Practices No 5: - Detecting .NET application memory leaksDownload WindowsAppMemoryLeak - 34.04 KB Introduction Avoid task manager to detect memory leak Using private bytes performance counters to detect memory leak 3 step process to investigate memory leak What is the type of memory leak? Total Memory = Managed memory + unmanaged memory How is the memory leak happening? Where is the memory leak? Source code Thanks, Thanks and Thanks

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My other .NET best practices article

IntroductionMemory leaks in .NET application have always being programmers nightmare. Memory leaks are biggest problems when it comes to production servers. Productions servers normally need to run with least down time. Memory leaks grow slowly and after sometime they bring down the server by consuming huge chunks of memory. Maximum time people reboot the system, make it work temporarily and send a sorry note to the customer for the downtime. Please feel free to download my free 500 question and answer eBook which covers .NET , ASP.NET , SQL Server , WCF , WPF , WWF@ http://www.questpond.com .

See Also...Visual Leak Detector - Enhanced Memory Leak Detection for Visual C++ Silverlight application memory leaks detector The ASP.NET Worker Process Part 1 Memory(-Leak) and Exception Trace (CRT and COM Leaks) Memory Leak Detection in .NET Memory Leak Detection

Avoid task manager to detect memory leaksThe first and foremost task is to confirm that there is a memory leak. Many developers use windows task manager to confirm, is there a memory leak in the application?. Using task manager is not only misleading but it also does not give much information about where the memory leak is.

.NET Best Practice No: 1:- Detecting High Memory consuming functions in .NET code Memory Leakage in Internet Explorer - revisited Detecting Memory Leaks using the CrtDbg Library Easy Detection of Memory Leaks Best Practice No 4:- Improve bandwidth performance of ASP.NET sites using IIS compression COM+ and .NET - A practical approach - Part 1 WPF GIF Animation Windows Mobile, iPhone, Android Marketplace Comparison GDI+ and MFC memory leak detection

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First lets try to understand how the task manager memory information is misleading. Task manager shows working set memory and not the actual memory used, ok so what does that mean. This memory is the allocated memory and not the used memory. Adding further some memory from the working set can be shared by other processes / application.

So the working set memory can big in amount than actual memory used.

Using private bytes performance counters to detect memory leak

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In order to get right amount of memory consumed by the application we need to track the private bytes consumed by the application. Private bytes are those memory areas which are not shared by other application. In order to detect private bytes consumed by an application we need to use performance counters. Below are the steps we need to follow to track private bytes in an application using performance counters:Start you application which has memory leak and keep it running. Click start Goto run and type perfmon. Delete all the current performance counters by selecting the counter and deleting the same by hitting the delete button. Right click , select Add counters , select process from performance object. From the counter list select Private bytes. From the instance list select the application which you want to test memory leak for. If you application shows a steady increase in private bytes value that means we have a memory leak issue here. You can see in the below figure how private bytes value is increasing steadily thus confirming that application has memory leak.

The above graph shows a linear increase but in live implementation it can take hours to show the uptrend sign. In order to check memory leak you need to run the performance counter for hours or probably days together on production server to check if really there is a memory leak.

3 step process to investigate memory leakOnce we have confirmed that there is a memory leak, its time to investigate the root problem of the memory leak. We will divide our journey to the solution in 3 phases what, how and where. What: - We will first try to investigate what is the type of memory leak, is it a managed memory leak or an unmanaged memory leak. How: - What is really causing the memory leak. Is it the connection object, some kind of file who handle is not closed etc? Where: - Which function / routine or logic is causing the memory leak.

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What is the type of memory leak? Total Memory = Managed memory + unmanaged memoryBefore we try to understand what the type of leak is, lets try to understand how memory is allocated in .Net applications. .NET application have two types of memory managed memory and unmanaged memory. Managed memory is controlled by garbage collection while unmanaged memory is outside of garbage collectors boundary.

So the first thing we need to ensure what is the type of memory leak is it managed leak or unmanaged leak. In order to detect if its a managed leak or unmanaged leak we need to measure two performance counters. The first one is the private bytes counter for the application which we have already seen in the previous session. The second counter which we need to add is Bytes in all heaps. So select .NET CLR memory in the performance object, from the counter list select Bytes in all heaps and the select the application which has the memory leak.

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Private bytes are the total memory consumed by the application. Bytes in all heaps are the memory consumed by the managed code. So the equation becomes something as shown in the below figure.

Un Managed memory + Bytes in all helps = private bytes, so if we want to find out unmanaged memory we can always subtract the bytes in all heaps from the private bytes. Now we will make two statements:If the private bytes increase and bytes in all heaps remain constant that means its an unmanaged memory leak. If the bytes in all heaps increase linearly that means its a managed memory leak. Below is a typical screenshot of unmanaged leak. You can see private bytes are increasing while bytes in heaps remain constant

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Below is a typical screen shot of a managed leak. Bytes in all heaps are increasing.

How is the memory leak happening?Now that we have answered what type of memory is leaking its time to see how is the memory leaking. In other words who is causing the memory leak ?. So lets inject an unmanaged memory leak by calling Marshal.AllocHGlobal function. This function allocates unmanaged memory and thus injecting unmanaged memory leak in the application. This command is run within the timer number of times to cause huge unmanaged leak.

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Collapse | Copy Code

private void timerUnManaged_Tick(object sender, EventArgs e) { Marshal.AllocHGlobal(7000); }

Its very difficult to inject a managed leak as GC ensures that the memory is reclaimed. In order to keep things simple we simulate a managed memory leak by creating lot of brush objects and adding them to a list which is a class level variable. Its a simulation and not a managed leak. Once the application is closed this memory will be reclaimed.Collapse | Copy Code

private void timerManaged_Tick(object sender, EventArgs e) { for (int i = 0; i < 10000; i++) { Brush obj = new SolidBrush(Color.Blue); objBrushes.Add(obj); } }

In case you are interested to know how leaks can happen in managed memory you can refer to weak handler for more information http://msdn.microsoft.com/en-us/library/aa970850.aspx . The next step is to download debugdiag tool from http://www.microsoft.com/DOWNLOADS/details.aspx?FamilyID=28bd5941c458-46f1-b24d-f60151d875a3&displaylang=en Start the debug diagnostic tool and select Memory and handle leak and click next.

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Select the process in which you want to detect memory leak.

Finally select Activate the rule now.

Now let the application run and Debugdiag tool will run at the backend monitoring memory issues.

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Once done click on start analysis and let the tool the analysis.

You should get a detail HTML report which shows how unmanaged memory was allocated. In our code we had allocated huge unmanaged memory using AllochGlobal which is shown in the report below. Type Description mscorlib.ni.dll is responsible for 3.59 MBytes worth of outstanding allocations. The following are the top 2 memory consuming functions: Warning System.Runtime.InteropServices.Marshal.AllocHGlobal(IntPtr): 3.59 MBytes worth of outstanding allocations.

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ntdll.dll is responsible for 270.95 KBytes worth of outstanding allocations. The following are the top 2 memory consuming functions: Warning ntdll!RtlpDphNormalHeapAllocate+1d: 263.78 KBytes worth of outstanding allocations. ntdll!RtlCreateHeap+5fc: 6.00 KBytes worth of outstanding allocations.

Managed memory leak of brushes are shown using GdiPlus.dll in the below HTML report. Type Description GdiPlus.dll is responsible for 399.54 KBytes worth of outstanding allocations. The following are the top 2 memory consuming functions: GdiPlus!GpMalloc+16: 399.54 KBytes worth of outstanding allocations.

Warning

Where is the memory leak?Once you know the source of memory leak is, its time to find out which logic is causing the memory leak. There is no automated tool to detect logic which caused memory leaks. You need to manually go in your code and take the pointers provided by debugdiag to conclude in which places the issues are. For instance from the report its clear that AllocHGlobal is causing the unmanaged leak while one of the objects of GDI is causing the managed leak. Using these details we need to them go in the code to see where exactly the issue lies.

Source codeYou can download the source code from the top of this article which can help you inject memory leak.

Thanks, Thanks and ThanksIt would be unfair on my part to say that the above article is completely my knowledge. Thanks for all the lovely people down who have written articles so that one day someone like me can be benefit. http://blogs.msdn.com/tess/ A great blog by a lovely lady Tess on debuggers. There are some great labs on memory leak detection using windbg , do not miss it. Tess god bless you, your blog rocks like anything. http://msdn.microsoft.com/en-us/magazine/cc163491.aspx This is a great article by James kovacs on managed and unmanaged memory leaks, must to read. http://davybrion.com/blog/2009/08/finding-memory-leaksin-silverlight-with-windbg/ Great article on finding memory leaks using windbg. http://www.itwriting.com/dotnetmem.php :- Great link which explains in detail the difference between working set memory and private bytes. http://www.microsoft.com/DOWNLOADS

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/details.aspx?FamilyID=28bd5941-c458-46f1-b24d-f60151d875a3& displaylang=en Download for the debugdiag tool. http://blogs.msdn.com/davidklinems/archive/2005/11 /16/493580.aspx David Kline explains the 3 common causes of memory leak in managed application.

My other .NET best practices article.NET best practice 1:- In this article we discuss about how we can find high memory consumption areas in .NET. You can read about the same at http://www.codeproject.com/KB/aspnet/BestPrctice1.aspx.aspx .NET best practice 2:- In this article we discuss how we can improve performance using finalize / dispose pattern. http://www.codeproject.com /KB/aspnet/DONETBestPracticeNo2.aspx .NET best practice 3:- How can we use performance counters to gather performance data from .NET applications http://www.codeproject.com /KB/aspnet/DOTNETBestPractices3.aspx .NET best practice 4 :- How can we improve bandwidth performance using IIS compression DotNetBestPractices4.aspx.

LicenseThis article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Shivprasad koirala I am a Microsoft MVP for ASP/ASP.NET and currently a CEO of a small E-learning company in India. We are very much active in making training videos , writing books and corporate trainings. Do visit my site for .NET, C# , design pattern , WCF , Silverlight , LINQ , ASP.NET , ADO.NET , Sharepoint , UML , SQL Server training and Interview questions and answers

Architect http://www.questpond.com India Member

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Update Refresh my mind My vote of 5 I don't find any process in the "Instances" list in perfmon My vote of 5 Empty Windows Service still shows memory leaks. My vote of 5 Excellent article My vote of 5 My vote of 5 Useful Article Message Automatically Removed Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk Re: Useless Indian Jerk [modified] My Vote of 5 Where is article 1 Re: Where is article 1 Re: Where is article 1 Re: Where is article 1 Last Visit: 19:00 31 Dec '99 General Rant News Admin Mast Avalons Dom P Member 7928159 Knight1219 ludwigs3rd Eric Xue (brokensnow) Michael Bakker mburnie santosh poojari Faddel mypaljohn KunalChowdhury Tom Clement Kunal_Chowdhury Ashish Kaila Shivprasad koirala Lloyd Atkinson Johnny J. Lloyd Atkinson Johnny J. ScruffyDuck gaurav_verma_mca Shivprasad koirala gaurav_verma_mca Shivprasad koirala First Prev Next 1:57 10 Jan '12 9:07 5 Jan '12 2:41 1 Jul '11 15:37 27 Sep '10 8:36 21 Sep '10 22:17 6 Sep '10 5:23 30 Aug '10 23:28 26 Aug '10 3:30 23 Aug '10 5:57 21 Aug '10 0:54 21 Aug '10 3:12 21 Aug '10 10:15 29 Jul '11 17:25 29 Jul '11 5:05 21 Aug '10 10:01 21 Aug '10 3:10 22 Aug '10 4:58 22 Aug '10 6:26 22 Aug '10 7:54 22 Aug '10 0:17 21 Aug '10 21:35 27 Nov '09 22:03 27 Nov '09 18:35 28 Nov '09 18:36 28 Nov '09 1 2 3 Next Bug Answer Joke

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Best Practices No 5 - Detecting .NET Application Memory Leaks

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