Programming with .NET Compact Framework 1.0 and SQL CE 2.0 : Part II

Background

In this article I am going to talk about garbage collection and JIT process in .NET compact framework and what are the differences between these two model of framework .

In my previous article I have explained how to develop application target to pocket PC  using .NET compact framework and MS-SQL CE  the article will be incomplete without talking about garbage collector and JIT in .NET compact framework .In this article I am going to explain about Garbage Collector / the garbage collection process  and JIT process in .NET compact framework.

As we all know in .NET the garbage collection happens automatically and  it is a un-deterministic process .The garbage collection in compact framework initiate in different ways like if the managed heap is not enough to allocate new objects or forcefully calling of GC.Collect() or if the size of object allocation in heap is more then 750 KB.

There are certain differences between .NET compact framework garbage collector and .NET framework garbage collection like as I have mention .NET compact framework design for memory constrains devices such as Pocket PC or smart phone but the .NET framework  is a platform to run different flavors of application like desktop or web based application. It has two types of garbage collector one is workstation garbage collector (Mscorwks.dll) and other is server garbage collector(Mscorsvr.dll) .Server garbage collector is much efficient then workstation garbage collector for more information click here as such .NET compact framework is concern its neither usages any of these garbage collector but it is using single collection model  garbage collector .

The other interesting things are .NET framework usages generation mechanism to collect dead objects and survival objects are promote to higher/next generation but .NET compact does not have generation model to collect objects  that mean while garbage collection process it collect all dead objects ,compact  heap and rearrange the survival objects. This is one of the key difference between two type of framework .Some time .NET compact framework free code that has jitted earlier in order to conserve memory for further allocation but .NET framework never does any code pitching for memory saving.

The garbage collection process in .NET compact framework is almost identical as .NET framework garbage collection process  like before garbage collection CLR brings all threads to safe point , examine the objects in managed heap for collection , collect all dead objects , compact the heap , reset the survival objects and some time release the pre-jitted code for additional memory .

Lets talk about the Jitting process in .NET compact framework , as we all aware that the IL code converts ( on demand)  into x86 code on the target system by the JIT compiler for example When a method is called, it is detected that there is no x86 code (native code) for the method, so IL is compiled into x86 code and executed, next time the method is called the x86 code gets executed, which means the execution of the method will be faster  for subsequent calls and leverage the application performance . In .NET compact framework is the jitted code cached in managed heap that means it will be part of garbage collection process when the  full GC happens ( called code pitching) , compact framework can jit the code up to 64 KB only if the code exceeds the limit then split the code into multiple methods and as I told earlier it does not support ngen to pre-compile your assemblies to native images.Finally compact framework support two types of JIT called iJIT and sJIT. iJIT managed call-stack as linked list where as sJIT managed call-stack as liner manner.

For more information

http://blogs.msdn.com/mikezintel/archive/2004/12/08/278153.aspx
http://blogs.msdn.com/stevenpr/archive/2004/07/26/197254.aspx