Re: Edit and continue feature - C# Discussion Boards

George_George28-Apr-08 3:52

28-Apr-08 3:52

Thanks Luc,

I think for console and Windows Service application, we should never use Application.Exit, right?

regards,
George

Re: Application.Exit

Luc Pattyn28-Apr-08 4:26

Luc Pattyn

28-Apr-08 4:26

Application.Exit() causes Application.Run() to return, both make sense in windows apps only.
this has been asked and answered many times in the last couple of days, it is not going
to change any time soon ...

Smile | :)

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Re: Application.Exit

George_George28-Apr-08 4:47

George_George

28-Apr-08 4:47

Thanks Luc,

Question answered.

regards,
George

Re: Application.Exit

PIEBALDconsult27-Apr-08 4:18

PIEBALDconsult

27-Apr-08 4:18

I never use Application.Exit; I just call the form's Close method.

Re: Application.Exit

George_George27-Apr-08 4:24

George_George

27-Apr-08 4:24

Thanks PIEBALDconsult,

I just want to confirm in console and Windows service application, we should not use Application.Exit to terminate the process, right?

regards,
George

Edit and continue feature

George_George26-Apr-08 22:06

George_George

26-Apr-08 22:06

Hello everyone,

Mentioned in the book -- "CLR via C#", page 15, chapter 1 "The CLR's Execution Model",

--------------------
the C# compiler will emit NOP (no-operation) instructions into the code. The NOP instructions are emitted to enable edit-and-continue feature while debugging.
--------------------

What means "edit-and-continue" feature? Why emitting NOP instructions will facilitate this feature?

thanks in advance,
George

Re: Edit and continue feature

Urs Enzler26-Apr-08 22:42

Urs Enzler

26-Apr-08 22:42

Hi George

Edit and Continue is that you can stop the running program on a break point, change the code in that method and continue the execution, i.e. you can code while debugging.

Why the compiler adds nops, I don't know Smile | :)

Urs

-^-^-^-^-^-^-^-
no risk no funk

Re: Edit and continue feature

George_George26-Apr-08 22:49

George_George

26-Apr-08 22:49

Thanks Urs,

I am also wondering why NOP instructions will facilitate edit-and-continue feature. Let us wait for comments from others. Smile | :)

regards,
George

Re: Edit and continue feature

Anthony Mushrow27-Apr-08 0:37

Anthony Mushrow

27-Apr-08 0:37

Perhaps it replaces the NOP's with any new sets of instructions if you edit your code while debugging.
I don't really know, but it seems quite possible.

My current favourite word is: Bacon!

-SK Genius

Re: Edit and continue feature

George_George27-Apr-08 1:42

George_George

27-Apr-08 1:42

Interesting point, SK!

But the developer when debugging may insert as many instructions as possible. How many NOP instructions of IL will be generated? Smile | :)

regards,
George

Re: Edit and continue feature

Anthony Mushrow27-Apr-08 2:10

Anthony Mushrow

27-Apr-08 2:10

I didn't mean it would replace just the NOP instruction with other instructions. Infact, thats quite difficult since a NOP is 1 byte and most other instructions are more like 3bytes+

I meant instead of the debugger having to start inserting extra instructions after the current one, or before it. It can just replace (and expand) the current instruction (which is just a NOP).

But of course, what if you remove instructions, what happens then?
I think the answer to this is way beyond me Confused | :confused:

My current favourite word is: Bacon!

-SK Genius

Re: Edit and continue feature

George_George27-Apr-08 2:21

George_George

27-Apr-08 2:21

Thanks SK,

I agree with the basic policy you posted above. But suppose I can copy and paste a large code segment into current function, save it and continue to run. In this case, I do not think compiler will be smart enough to know in advance I will past a lot of code and will reserve a lot of NOP operations. Any comments? Smile | :)

regards,
George

A new idea

Anthony Mushrow27-Apr-08 2:15

Anthony Mushrow

27-Apr-08 2:15

Pehaps they are just there for somewhere for execution of the program to wait at, safely without fear of the current instruction changing.

If you stopped on something like push 01 and you wanted to change that to push 02 and exection had paused on that instruction, would it be able to change it? Whereas if you where stopped on a NOP then the instruction will never be changed even if everything else around it is.

I think we need some kinda expert on this one.

My current favourite word is: Bacon!

-SK Genius

Re: A new idea

George_George27-Apr-08 2:25

George_George

27-Apr-08 2:25

Thanks SK!

I think it has nothing to do with NOP. It is how the function of debugger is designed -- does it allowed to change current statement or not (not means only be able to change statement from next statement to execute). Any comments?

regards,
George

Re: Edit and continue feature [modified]

Roger Alsing27-Apr-08 2:38

Roger Alsing

27-Apr-08 2:38

Here is my guess:

If the compiler inserts a few nops at the _begining_ of a method, it can then replace those nops with a call + ret to another method.

thus it can re emit the entire method with all the changes, and just make a redirect from the original method to the altered method. thus not having to worry about adding too many or removing operands in the original body.

eg (pseudo):

original:

public int Foo()
{
    nop
    Console.Write("hello");
    return 1;
}

altered:

public int Foo()
{
    return RuntimeModifiedFoo(); //replaced nop with this call and return

    //will not execute
    Console.Write("hello");
    return 1;
}

//runtime emitted:
public int RuntimeModifiedFoo()
{
    Console.Write("hello");
    Console.WriteLine ("modified method");
    return 123;
}

And if you edit even more, it simply replace the first "return RuntimeModifiedFoo();" with a "return RuntimeModifiedFoo#2();"

MS introduced DynamicMethod http://msdn2.microsoft.com/en-us/library/system.reflection.emit.dynamicmethod.aspx[^]

in .NET 2, and that was at the same time as C# got edit and continue..

My 2 cents Smile | :)

Blog: http://www.rogeralsing.com
Projects: http://www.puzzleframework.com

modified on Sunday, April 27, 2008 8:47 AM

Re: Edit and continue feature

George_George27-Apr-08 2:49

George_George

27-Apr-08 2:49

Interesting and smart, Roger!

A further question, if we do not inser NOP, what are the additional efforts?

regards,
George

Re: Edit and continue feature

Roger Alsing27-Apr-08 3:07

Roger Alsing

27-Apr-08 3:07

I think it might be impossible to do it w/o inserting the nop.

Lets say that we have an empty method that we want to modify.

public void Foo()
{
//empty
}

and lets pretend that it looks like this in memory:

1000000 ret //start and end of foo , we can only alter this single byte w/o overwriting the next methiod
1000001 start of next method

There would simply not be any space for us to insert the call to the modified method there, we can only alter 1 byte and if we alter more we start to overwrite some other method.

(But again, I do not know if my guess is how it works, but Id say it would be the easiest approach.)

Blog: http://www.rogeralsing.com
Projects: http://www.puzzleframework.com

Re: Edit and continue feature

George_George27-Apr-08 3:30

George_George

27-Apr-08 3:30

Thanks Roger,

Your idea is cool. Let me know if you have found any related documents. I am interested in this topic. Smile | :)

regards,
George

Re: Edit and continue feature

Daniel Grunwald27-Apr-08 11:59

Daniel Grunwald

27-Apr-08 11:59

In the debugger, you can also set breakpoints on lines like "{" "}". Breakpoints can be only set on instructions, so the C# compiler has to emit NOPs for those lines.

I don't know if edit-and-continue needs any additional NOPs.

Re: Edit and continue feature

George_George27-Apr-08 17:40

George_George

27-Apr-08 17:40

Cool, Daniel!

Let us see if other people has experience to share why emitting NOP will facilitate edit-and-continue feature?

regards,
George

Re: Edit and continue feature

Roger Alsing27-Apr-08 20:56

Roger Alsing

27-Apr-08 20:56

Daniel is correct, I verified this with reflector:

static void Main(string[] args)
        {
            if(true)
            {
                Console.Write("hello");
                {
                    {
                        {
                        }
                    }
                }
            }
        }

got emitted as:

.method private hidebysig static void Main(string[] args) cil managed
{
    .entrypoint
    .maxstack 1
    .locals init (
        [0] bool CS$4$0000)
    L_0000: nop 
    L_0001: ldc.i4.0 
    L_0002: stloc.0 
    L_0003: nop 
    L_0004: ldstr "hello"
    L_0009: call void [mscorlib]System.Console::Write(string)
    L_000e: nop 
    L_000f: nop 
    L_0010: nop 
    L_0011: nop 
    L_0012: nop 
    L_0013: nop 
    L_0014: nop 
    L_0015: nop 
    L_0016: ret 
}