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.NET Forum / .NET Framework / CLR / April 2007GB.Collect() can be trusted?
Hi, I'm wondering if the GC.Collect method really collects all objects possible objects? Or is this still a "smart" process sometimes keeping objects alive even if they can be garbage collected? I need to know because I'm looking for memory leaks in an application. It would be really helpful to be able to determine if an object after manually invoking the GC.Collect is only kept alive because it still being referenced by other alive objects in contrast to being alive because the GC.Collect didn't found it necessary to collect the object, even when asked explicitly. Regards, Ward GC.Collect is documented as "Use this method to attempt to reclaim all memory that is inaccessible. However, the Collect method does not guarantee that all inaccessible memory is reclaimed". I can't think of any reason why the GC won't collect all inaccessible memory. WinDbg and SOS are a little more helpful at what you're describing.  SignatureBrowse http://connect.microsoft.com/VisualStudio/feedback/ and vote. http://www.peterRitchie.com/blog/ Microsoft MVP, Visual Developer - Visual C# > Hi, > [quoted text clipped - 13 lines] > > Ward > I can't think of any reason why the GC won't collect all inaccessible > memory. The only thing that comes to mind is fragmentation. GC.Collect typically does the collection and them performs a compaction. When the heap is fragmented, that compaction doesn't work very well, and you can end up without much "free" memory... SignatureChris Mullins, MCSD.NET, MCPD:Enterprise, Microsoft C# MVP http://www.coversant.com/blogs/cmullins That shouln't cause a particular object to not be collected though. My interpretation of "memory leak" could have been different than yours or Ward's. Mine what that a particular object wasn't collected... I don't pay attention to usable space as an indiciation of memory leaks. Due, as you say, to fragmentation... SignatureBrowse http://connect.microsoft.com/VisualStudio/feedback/ and vote. http://www.peterRitchie.com/blog/ Microsoft MVP, Visual Developer - Visual C# > > I can't think of any reason why the GC won't collect all inaccessible > > memory. [quoted text clipped - 4 lines] > When the heap is fragmented, that compaction doesn't work very well, and you > can end up without much "free" memory... I agree - this wouldn't at all cause something to not be collected. The original poster should be able to use one of the existing tools (Scitech's Memory Profiler, Red Gate's Memory Profiler, heck - even WinDbg with SOS can do this), walk the root paths, and see why his object wasn't collected. It should be pretty easy. The tools have recently started getting so very good. Red Gate & SciTech now have x64 support, SciTech can load in MiniDump files so you can do post-crash memory analysis - it makes debugging so much easier than it used to be. SignatureChris Mullins, MCSD.NET, MCPD:Enterprise, Microsoft C# MVP http://www.coversant.com/blogs/cmullins > That shouln't cause a particular object to not be collected though. > [quoted text clipped - 13 lines] >> you >> can end up without much "free" memory... Thanks guys for your help, More discussion of this thread can be found here: news://news.microsoft.com:119/e0ZNz6mgHHA.4704@TK2MSFTNGP06.phx.gbl Hello, > I need to know because I'm looking for memory leaks in an application. Maybe you should rather use a memory profiler, such as dotTrace, for example? That way you'll clearly see the objects that are “leaked” and trace the references that are preventing them from being reclaimed. (H) Serge YourKit .NET profiler shows GC activity and has tools for memory leak hunting http://www.yourkit.com/dotnet/ GR, Sergey
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