Throw when setting OnStarting after response has already started (#806).

[cesarblum]

#806

@halter73 @mikeharder @pakrym

[mikeharder]

Would it be worthwhile to add a functional test as well, showing how customer code would set OnStarting()?

[benaadams]

Use an enum rather than a string; string version is additional calls, better to push it out to the infrequently called function. (related background info dotnet/coreclr#6634 (comment))

[cesarblum]

You did that in #962, right? I can change this if we take it 😄

[benaadams]

I'll get a move on 😉

[cesarblum]

@benaadams Could you elaborate on your first comment about using an enum? Not sure what's going on there.

[benaadams]

So with the string it inserts a load string call then calls the function

mov      ecx, 0x498F
call     CORINFO_HELP_STRCNS_CURRENT_MODULE
mov      rcx, rax
call     Frame:ThrowResponseAlreadyStartedException(ref)

With the enum it just sets a value

mov      ecx, 3
call     Frame:ThrowResponseAlreadyStartedException(int)

It does push the load string off to Frame:ThrowResponseAlreadyStartedException as the string still needs to get loaded; but that doesn't really ever get called, so the main function is more trim and the instruction cache hotter.

[benaadams]

Also hopefully it will also soon consistently move those calls to the bottom of the function as seen in this example (from dotnet/coreclr#6634 (comment))

Jit inline decisions (decides not to inline the functions that throw [no-return])

Inlines into 06002A67 ArraySegment`1:.ctor(ref,int,int):this
  [0 IL=0004 TR=000067 06000C7B] [FAILED: does not return] ThrowHelper:ThrowArgumentNullException(int)
  [0 IL=0016 TR=000061 06000C69] [FAILED: does not return] ThrowHelper:ThrowArgumentOutOfRangeException(int,int)
  [0 IL=0028 TR=000054 06000C69] [FAILED: does not return] ThrowHelper:ThrowArgumentOutOfRangeException(int,int)
  [0 IL=0043 TR=000048 06000C77] [FAILED: does not return] ThrowHelper:ThrowArgumentException(int)
Budget: initialTime=270, finalTime=270, initialBudget=2700, currentBudget=2700
Budget: initialSize=1727, finalSize=1727

Moves the calling of the throw functions out of the flow, even though they were at the start to a section called "cold code" (which is also does for straight throws, but they have more preamble than a function call)

; Assembly listing for method ArraySegment`1:.ctor(ref,int,int):this
; Emitting BLENDED_CODE for X64 CPU with SSE2
; optimized code
; rsp based frame
; partially interruptible
; Final local variable assignments
;
;  V00 this         [V00,T00] (  5,   5  )   byref  ->  rsi         this
;* V01 TypeCtx      [V01    ] (  0,   0  )    long  ->  zero-ref   
;  V02 arg1         [V02,T01] (  5,   5  )     ref  ->   r8        
;  V03 arg2         [V03,T02] (  5,   5  )     int  ->  rdi        
;  V04 arg3         [V04,T03] (  3,   3  )     int  ->  rbx        
;  V05 loc0         [V05    ] (  1,   1  )  lclBlk (32) [rsp+0x00]  
;
; Lcl frame size = 32
G_M41510_IG01:
       push     rdi
       push     rsi
       push     rbx
       sub      rsp, 32
       mov      rsi, rcx
       mov      edi, r9d
       mov      ebx, dword ptr [rsp+60H]
G_M41510_IG02:
       test     r8, r8
       je       G_M41510_IG08
G_M41510_IG03:
       test     edi, edi
       jl       G_M41510_IG09
G_M41510_IG04:
       test     ebx, ebx
       jl       G_M41510_IG10
G_M41510_IG05:
       mov      edx, dword ptr [r8+8]
       sub      edx, edi
       cmp      edx, ebx
       jl       G_M41510_IG11
G_M41510_IG06:
       mov      rcx, rsi
       mov      rdx, r8
       call     CORINFO_HELP_CHECKED_ASSIGN_REF
       mov      dword ptr [rsi+8], edi
       mov      dword ptr [rsi+12], ebx
G_M41510_IG07:
       add      rsp, 32
       pop      rbx
       pop      rsi
       pop      rdi
       ret      
************** Beginning of cold code **************
G_M41510_IG08:
       mov      ecx, 3
       call     ThrowHelper:ThrowArgumentNullException(int)
G_M41510_IG09:
       mov      ecx, 41
       mov      edx, 4
       call     ThrowHelper:ThrowArgumentOutOfRangeException(int,int)
G_M41510_IG10:
       mov      ecx, 16
       mov      edx, 4
       call     ThrowHelper:ThrowArgumentOutOfRangeException(int,int)
G_M41510_IG11:
       mov      ecx, 23
       call     ThrowHelper:ThrowArgumentException(int)
       int3     
; Total bytes of code 132, prolog size 7 for method ArraySegment`1:.ctor(ref,int,int):this

[mikeharder]

from me, though you might want to review @benaadams comment.

[davidfowl]