Turning off JIT, and controlling codeflow in MSIL (own VM)

Question

Hi, I'm writing my own scripting language in C#, with some features I like, and I chose to use MSIL as output's bytecode (Reflection.Emit is quite useful, and I dont have to think up another bytecode). It works, emits executable, which can be run ( even decompiled with Reflector :) )and is quite fast.

But - I want to run multiple 'processes' in one process+one thread, and control their assigned CPU time manually (also implement much more robust IPC that is offered by .NET framework) Is there any way to entirely disable JIT and create own VM, stepping instruction-after-instruction using .NET framework (and control memory usage, etc.), without need to write anything on my own, or to achieve this I must write entire MSIL interpret?

EDIT 1): I know that interpreting IL isn't the fastest thing in the universe :)

EDIT 2): To clarify - I want my VM to be some kind of 'operating system' - it gets some CPU time and divides it between processes, controls memory allocation for them, and so on. It doesnt have to be fast, nor effective, but just a proof of concept for some of my experiments. I dont need to implement it on the level of processing every instruction - if this should be done by .NET, I wont mind, i just want to say : step one instruction, and wait till I told you to step next.

EDIT 3): I realized, that ICorDebug can maybe accomplish my needs, now looking at implementation of Mono's runtime.

Answer 1

You could use Mono - I believe that allows an option to interpret the IL instead of JITting it. The fact that it's open source means (subject to licensing) that you should be able to modify it according to your needs, too.

Mono doesn't have all of .NET's functionality, admittedly - but it may do all you need.

Answer 2

Beware that MSIL was designed to be parsed by a JIT compiler. It is not very suitable for an interpreter. A good example is perhaps the ADD instruction. It is used to add a wide variety of value type values: byte, short, int32, int64, ushort, uint32, uint64. Your compiler knows what kind of add is required but you'll lose that type info when generating the MSIL.

Now you need to find it back at runtime and that requires checking the types of the values on the evaluation stack. Very slow.

An easily interpreted IL has dedicated ADD instructions like ADD8, ADD16, etc.

Answer 3

Microsofts implementation of the Common Language Runtime has only one execution system, the JIT. Mono, on the other hand comes with both, a JIT and an interpreter.

I, however, do not fully understand what exactly you want to do yourself and what you would like to leave to Microsofts implementation:

Is there any way to entirely disable JIT and create own VM?

and

... without need to write anything on my own, or to achieve this I must write entire MSIL interpret?

is sort of contradicting.

If you think, you can write a better execution system than microsofts JIT, you will have to write it from scratch. Bear in mind, however, that both microsofts and monos JIT are highly optimized compilers. (Programming language shootout)

Being able to schedule CPU time for operating system processes exactly is not possible from user mode. That's the operating systems task.

Some implementation of green threads might be an idea, but that is definitely a topic for unmanaged code. If that's what you want, have a look at the CLR hosting API.

I would suggest, you try to implement your language in CIL. After all, it gets compiled down to raw x86. If you don't care about verifiability, you can use pointers where necessary.