[M3devel] help debugging Juno..sanity check?

[Tony Hosking]

Huh?  I don't understand the point of all of this.  Threads can be  
moved by the GC, even if referenced from globals.  The only way to  
prevent a thread moving is to keep a reference to it on some thread  
stack.  (I still don't know what you are trying to achieve -- why not  
use a hardware breakpoint in the debugger?).  That's how I found the  
race in ScrollerVBTClass.m3.

On 28 Sep 2009, at 09:11, Jay K wrote:

> So, I know that ThreadWin32.T instances are prone to being  
> overwritten.
>
> So I did this:
>
>
>   T = BRANDED "Thread.T Win32-1.0" OBJECT
> >      pad1: ARRAY [0..16_1000] OF CHAR;
> >      protect: ARRAY [0..16_1] OF CHAR;
> >      pad2: ARRAY [0..16_1000] OF CHAR;
>
> And then there are two occurences of NEW(T):
>
>
>       next_self          := NEW(T);
> >      Protect(next_self);
>
>
> PROCEDURE CreateT (act: Activation): T =
>   (* LL = 0, because allocating a traced reference may cause
>      the allocator to start a collection which will call  
> "SuspendOthers"
>      which will try to acquire "activeMu". *)
>   VAR t := NEW(T, act := act);
>   BEGIN
> >    Protect(t);
>
>
> PROCEDURE Protect(t: T)=
> VAR old: WinDef.DWORD;
> BEGIN
>  EVAL WinBase.VirtualProtect(LOOPHOLE(ADR(t.protect), SIZE_T), 1,  
> PAGE_READONLY, ADR(old));
> END Protect;
>
>
> This should catch any writes to these fields.
>
>
> Now, a thread can be garbage collected and reused.
> And I'd want to unprotect this memory.
> Or prevent the garbage collector from deciding any thread is garbage.
>  Second option seems easier and suffices.
>
>
> So:
>
>
> VAR
> threads: ARRAY[0..2000] OF T;  (* big enough for our purposes *)
> threadCount: INTEGER;
>
>
> and more completely:
>
> PROCEDURE Protect(t: T)=
> VAR old: WinDef.DWORD;
> BEGIN
>  EVAL WinBase.VirtualProtect(LOOPHOLE(ADR(t.protect), SIZE_T), 1,  
> PAGE_READONLY, ADR(old));
>  RTIO.PutInt(threadCount);
>  RTIO.PutText(" ");
>  RTIO.PutAddr(ADR(threads));
>  RTIO.PutText(" ");
>  RTIO.PutAddr(ADR(t.protect));
>  RTIO.PutText("\n");
>  threads[threadCount] := t;
>  INC(threadCount);
> END Protect;
>
>
> And just in case, I emptied out the FreeSlot function.
>
>
> But yet I get:
>
> 0 0xe2abe0 0x1141021
> 1 0xe2abe0 0x114b429
> 2 0xe2abe0 0x11a2311
> 3 0xe2abe0 0x11a48b1
> 4 0xe2abe0 0x11ab499
> 5 0xe2abe0 0x12e9f11
> 6 0xe2abe0 0x12d211d
> 7 0xe2abe0 0x11bd691
> 8 0xe2abe0 0x11d1011
> 9 0xe2abe0 0x11d3e2d
> 10 0xe2abe0 0x11d6759
> 11 0xe2abe0 0x11d8bd1
> 12 0xe2abe0 0x12089f1
> 13 0xe2abe0 0x1211455
> 14 0xe2abe0 0x12138cd
> 15 0xe2abe0 0x1215ecd
> 16 0xe2abe0 0x12184cd
> 17 0xe2abe0 0x121bcd5
> 18 0xe2abe0 0x121e35d
> Grow (0x210000) => 0x2120000   total: 4.1M   span: 17.9M   density:  
> 23%
> (b60.9d4): Access violation - code c0000005 (first chance)
> First chance exceptions are reported before any exception handling.
> This exception may be expected and handled.
> eax=011b0000 ebx=00010000 ecx=00000060 edx=00000000 esi=011b0000  
> edi=011bd000
> eip=78545e37 esp=01cae5ec ebp=01cae5f0 iopl=0         nv up ei pl nz  
> na pe nc
> cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000              
> efl=00010206
> MSVCR90!fastzero_I+0x20:
> 78545e37 660f7f07        movdqa  xmmword ptr [edi],xmm0 ds: 
> 0023:011bd000=0000000
> 0000000000000000000000000
> 0:003> k
> ChildEBP RetAddr
> 01cae5f0 78545ea9 MSVCR90!fastzero_I+0x20
> 01cae610 005dad48 MSVCR90!_VEC_memzero+0x36
> 01cae634 005d1f34 m3core!RTMisc__Zero+0x1f
> 01cae68c 005c8191 m3core!RTHeapRep__LongAlloc+0xf3
> 01cae6d8 005c7793 m3core!RTAllocator__AllocTraced+0xec
> 01cae70c 005c728d m3core!RTAllocator__GetTracedObj+0x8c
> 01cae730 005d07d9 m3core!RTHooks__AllocateTracedObj+0x15
> 01cae784 005d033f m3core!RTCollector__CollectSomeInStateZero+0x45e
> 01cae798 005cffd6 m3core!RTCollector__CollectSome+0x6e
> 01cae7dc 005c817c m3core!RTHeapRep__CollectEnough+0x9b
> 01cae81c 005c7d06 m3core!RTAllocator__AllocTraced+0xd7
> 01cae858 005c7348 m3core!RTAllocator__GetOpenArray+0x97
> 01cae880 00f9f50d m3core!RTHooks__AllocateOpenArray+0x19
> 01cae930 00f9f201 m3ui!WinScrnPixmap__PixmapFromRaw__ConvertColor+0x8f
> 01cae958 00f9e22f m3ui!WinScrnPixmap__PixmapFromRaw+0x71
> 01cae9ac 00eb4121 m3ui!WinScrnPixmap__Load+0x320
> 01caeee4 00eb298d m3vbtkit!Image__ScaleRaw+0xb30
> 01caef44 00fb2b72 m3vbtkit!Image__ApplyScaled1+0x166
> 01caef70 00fc0af8 m3ui!VBTRep__PixmapApply+0xbf
> 01caefcc 00fa6766 m3ui!Palette__ResolvePixmap+0x7db
> 0:003> r edi
> edi=011bd000
> 0:003>
>
>
> What am I confused about?
>
> Why does it seem that even if I store some pointers in globals, they  
> are getting garbage collected and reused?
>
> I should debug BuildGlobalMap??
>
>  - Jay

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