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.NET Forum / Languages / C# / October 2007Metaprogramming
If you do metaprogramming in C#, is the generated code garbage collected or does it leak indefinitely?  SignatureDr Jon D Harrop, Flying Frog Consultancy http://www.ffconsultancy.com/products/?u > If you do metaprogramming in C#, is the generated code garbage collected > or does it leak indefinitely? Can you give an example? Regards, Mads SignatureMed venlig hilsen/Regards Systemudvikler/Systemsdeveloper cand.scient.dat, Ph.d., Mads Bondo Dydensborg Dansk BiblioteksCenter A/S, Tempovej 7-11, 2750 Ballerup, Tlf. +45 44 86 77 34 Regardless of how they come to be (Reflection.Emit, etc), dynamic assemblies are treated the same as regular assemblies; there is no good way to unload an assembly from an active appdomain. You can, however, load it into a second app-domain and then kill the app- domain. A good bet is to (for instance) use a static cache so that you don't end up creating the same code over and over, but simply re-use the assembly you emitted earlier. Executing code is treated as normal; instances will be collected (or not) using the same rules. Marc > If you do metaprogramming in C#, is the generated code garbage collected > or does it leak indefinitely? Without providing more detail, I find it difficult to be sure what you're really trying to do. If you dynamically create and load assemblies, you should probably load them into a new appdomain. You cannot unload an assembly, but you can discard an appdomain and discarding the appdomain will discard all the assemblies loaded into it with it. Ben > > If you do metaprogramming in C#, is the generated code garbage collected > > or does it leak indefinitely? > > Without providing more detail, I find it difficult to be sure what you're > really trying to do. I think he's trying to prove that F# is superior to C#. That's Jon Harrop's usual purpose on this group ;) Jon > I think he's trying to prove that F# is superior to C#. That's Jon > Harrop's usual purpose on this group ;) Interstingly, I think it is a valid discussion - but the important context is: "at what?". Functional languages do have advantages, especially in areas such as science / modelling - however, it isn't necessarily a great fit for the typical business application. It is *certainly* a much more meaningful discussion than the far-too- regular VB vs C# ;-p Marc > > I think he's trying to prove that F# is superior to C#. That's Jon > > Harrop's usual purpose on this group ;) [quoted text clipped - 3 lines] > especially in areas such as science / modelling - however, it isn't > necessarily a great fit for the typical business application. Absolutely. > It is *certainly* a much more meaningful discussion than the far-too- > regular VB vs C# ;-p True. I just wish Jon would get into it properly rather than just asking leading questions: "If you do X does C# behave badly", "Is C# going to give way to F#" etc. Jon >> > I think he's trying to prove that F# is superior to C#. That's Jon >> > Harrop's usual purpose on this group ;) [quoted text clipped - 14 lines] > > Jon Agree. In this way he's actually doing more harm than good for F# community. There are better ways to evangelize new ideas. > True. I just wish Jon would get into it properly rather than just > asking leading questions: "If you do X does C# behave badly", "Is C# > going to give way to F#" etc. You forget that he thinks ML is more used than C#. :-) Arne >> If you do metaprogramming in C#, is the generated code garbage collected >> or does it leak indefinitely? [quoted text clipped - 6 lines] > discard an appdomain and discarding the appdomain will discard all the > assemblies loaded into it with it. Right. I think I'm getting to grips with this. So you must deallocate code explicitly yourself, i.e. it is not garbage collected. To be able to deallocate code there is the technical issue of wrapping your assembly in an appdomain. I read somewhere that types cannot be collected but that makes sense because (I believe) the .NET platform prohibits structural subtyping. So all types are regarded as different even if they are structurally identical, e.g. if you define an (int, float) pair in two different assemblies then they are considered to be different types. So types have the same place as code in .NET from the point of view of allocation, and deallocating an appdomain will deallocate the types it defines. One final question: is code deallocation safe? So, if function A in assembly A' calls function B in assembly B' and you deallocate the appdomain containing B' before calling A, do you get a nice exception or a nasty access violation? SignatureDr Jon D Harrop, Flying Frog Consultancy http://www.ffconsultancy.com/products/?u <snip> > One final question: is code deallocation safe? So, if function A in assembly > A' calls function B in assembly B' and you deallocate the appdomain > containing B' before calling A, do you get a nice exception or a nasty > access violation? You'll get an AppDomainUnloadException. Jon >> One final question: is code deallocation safe? So, if function A in >> assembly A' calls function B in assembly B' and you deallocate the >> appdomain containing B' before calling A, do you get a nice exception or >> a nasty access violation? > > You'll get an AppDomainUnloadException. Ok. Can you garbage collect generated code by putting it in an app domain and wrapping the app domain in a class that uses a finalizer to explicitly deallocate the app domain? SignatureDr Jon D Harrop, Flying Frog Consultancy http://www.ffconsultancy.com/products/?u > > You'll get an AppDomainUnloadException. > [quoted text clipped - 3 lines] > wrapping the app domain in a class that uses a finalizer to explicitly > deallocate the app domain? I guess you probably could, yes. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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