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Windows Server 2008. How can I quickly use up RAM so to induce GC in my app. If there is a way to do it without needing Visual Studio or installing a language runtime it would be good.

EDIT: I don't want to have to write an app and then copy it over to the server. I'm looking for a way to do it quickly without writing an app that requires an IDE or installation of a runtime/compiler. Perhaps a powershell or batch script?...

Mr. Flibble
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    I'm curious as to why you would ever need or want to do this. In languages that are garbage collected, you should trust the garbage collector to do it's job properly. – Thomas Owens Nov 10 '09 at 18:54
  • I have a memory leak that disappears when I manually call GC :-/ – Mr. Flibble Nov 10 '09 at 18:59
  • @Mr Flibble: What language/runtime are you using? – Sam Harwell Nov 10 '09 at 19:01
  • @280Z28 Please see my edit in the question. – Mr. Flibble Nov 10 '09 at 19:02
  • @Mr Flibble: I mean what language/runtime is the application with the leak. – Sam Harwell Nov 10 '09 at 19:07
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    @Mr Flibble: If the leak disappears when you call garbage collection, doesn't that disqualify it as a 'leak'? – axel_c Nov 10 '09 at 19:14
  • Maybe you should just try to limit the amount of memory available to your app. – Nick Nov 10 '09 at 19:18
  • Operating systems don't have garbage collection. So a powershell or batch script will *never* be able to trigger garbage collection. It will instead use up the process heap, until the OS finally decides to terminate the process. This has *nothing* to do with the memory being used by your application. If your application is leaking memory, then you need to put a memory profiler on your application and figure out what's happening. – Daniel Pryden Nov 10 '09 at 19:19
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    who is minusing everybody without explaining why? those answers all made sense before the poster edited the question. he asked for answers, and said he would prefer a non programming way, but also implied programming answers were possible. – Peter Recore Nov 10 '09 at 19:23
  • @Daniel Pryden. Ok, thanks. I thought a memory shortage would cause GC earlier. My bad. My comment to Peter's question has more details. – Mr. Flibble Nov 10 '09 at 19:27
  • @axel_c I don't know. What is it called when your app slowly uses up more and more memory when it should (_in my mind..._) release it? – Mr. Flibble Nov 10 '09 at 19:29
  • @Peter. Aye, sorry about that. I didn't build an edit button into the site! I tried to imply that a programming was was bad by saying a 'non-programing' was would be good. Sorry for the bad description. – Mr. Flibble Nov 10 '09 at 19:34
  • @Mr. Flibble: In this case, your application is not leaking *managed* memory, but *unmanaged* resources. This is because you are using `IDisposable` objects without manually disposing of them. Eventually, the finalizer thread will get around to disposing of them (and forcing GC can help move that along) but the real problem is that you should be disposing of the unmanaged resources as soon as you aren't going to use them anymore. That's what the `using` statement is for in C#. – Daniel Pryden Nov 10 '09 at 19:35
  • @Daniel - as per my comment in Peter's question...Calling `Dispose` doesn't fix the problem. When you say 'Eventually, the finalizer thread will get around to disposing of them' do you mean only if I call IDisposable? I'm getting OutOfMemory exceptions so it isn't getting around to it in time. – Mr. Flibble Nov 10 '09 at 19:43
  • @Mr. Flibble: I suggest you open a new question to discuss your memory leak in your .NET application, since that will get you more useful responses. But I think you need to read up on `IDisposable` and finalizers. The garbage collector is only saving you from an `OutOfMemoryException` as a *side effect*, because GC is forcing finalizers to run. Open a new question and I'll add an answer explaining more clearly. – Daniel Pryden Nov 10 '09 at 19:48

3 Answers3

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I don't think using up RAM outside your process is going to necessarily trigger GC.

If I understand your question correctly, you have a program Foo.exe that is written in some unknown language, running on some unknown runtime (are you not allowed to post the details for some reason, or do you just not know?), and you want to try to get that program's runtime to trigger a garbage collection. However, you want to do this by using up RAM outside of foo.exe.

You could do this by creating a simple batch file that just started up a hundred copies of IE or Word or whatever program you want. However, I don't think that will do what you want it to do. If your process has already allocated a certain amount of memory, it won't necessarily give that memory up or trigger GC just because other processes are being started. It may page to disk, or may force other programs to page to disk. But not all Garbage Collectors are alike, so we can't really help without more details. I'm pretty sure some VM's never give back memory once they've allocated it, even after GC.

Peter Recore
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  • Thanks Peter. So an external shortage of memory (external to my app) won't induce garbage collection. My mistake. FWIW, I'm on the .NET runtime in IIS (ASP.NET MVC app). I've a LINQ2SQL datacontext which is instantiated using Windsor IoC container on a per-web-request basis. For some reason the LINQ2SQL datacontext is not getting GCed naturally and is causing OutOfMemory exceptions in my app. If I call GC manually when I am done with the datacontext the memory leak goes away. – Mr. Flibble Nov 10 '09 at 19:24
  • @Mr. Flibble: `DataContext` implements `IDisposable`. Are you properly disposing of it (e.g. with a `using` block)? – Daniel Pryden Nov 10 '09 at 19:28
  • Daniel, it isn't in a `using` block but I have tried calling `.Dispose` on it but it didn't have an effect. Calling GC does have an effect without calling `.Dispose` – Mr. Flibble Nov 10 '09 at 19:31
  • I would lay very good odds that your problem is that somewhere you have an `IDisposable` object that you aren't disposing of. The GC only manages "managed" allocations. In your case, you're doing LINQ to SQL, so your SQL Server driver will allocate big data objects directly from the OS (as "unmanaged" memory). The GC *cannot* release those objects back to the OS. All the GC can do is release the managed object that is holding a pointer to the unmanaged object. If you're lucky, the managed object will have a finalizer, and forcing GC will force that finalizer to run and release the object. – Daniel Pryden Nov 10 '09 at 19:40
  • But the whole reason the `IDisposable` interface exists is so you can *explicitly* release the unmanaged resources held by a managed object. So you should just go through your code, and every time you construct any object that implements `IDisposable`, make sure it's in a `using` block, or else that there's a `finally` clause that calls `.Dispose()`. – Daniel Pryden Nov 10 '09 at 19:41
  • @Daniel My problem (apart from that calling Dispost doesn't seem to work) is that I have no clue where to start a `using` block when the instance is created using Windsor IoC container. I guess I need to do some research. – Mr. Flibble Nov 10 '09 at 19:45
  • @Mr. Flibble: I think the real answer is that you probably shouldn't be creating `IDisposable` objects with an IoC container. This question may be useful to you, though: http://stackoverflow.com/questions/987761/how-do-you-reconcile-idisposable-and-ioc – Daniel Pryden Nov 10 '09 at 19:53
  • BTW, Peter: Sorry to hijack the comments on your answer like this. :-) Thanks for understanding... – Daniel Pryden Nov 10 '09 at 19:57
  • Part deux: http://stackoverflow.com/questions/1710992/linq-to-sql-datacontext-windsor-ioc-memory-leak-problem – Mr. Flibble Nov 10 '09 at 20:33
  • @Daniel - no problem. You are chiming in with lots of good details. my answer was pretty high level. – Peter Recore Nov 12 '09 at 16:46
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You could run your program inside a virtual machine such as Virtual Box, where you specify the memory ceiling of the guest operating system.

I'm having trouble imagining a scenario where this would be necessary though. Could you provide more information about the problem?

Karmic Coder
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If you are using java you can specify the max amount of memory using Xmx. Search for JVM memory setting

Nick
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