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I'm thinking you've got a buffer over-run
problem. Set a breakpoint on *memory* where you watch for that
rsThreadData to get changed. You'll have to set a breakpoint probably in
the ctor to then set this memory breakpoint, then you'll find every time this
memory changes and hopefully you'll see somewhere in your code that is changing
the memory.
This problem intrigues me and if you can zip up
the project where all I have to do is compile and run to make it blow up (or
maybe run two versions that talk to each other as that seems to be your case),
I'll be happy to take a look myself.
----- Original Message -----
Sent: Monday, February 21, 2005 10:26
AM
Subject: RE: [msvc] Overlapped Comms - It
Came Back To Bite Me
OK - I definitely appear to have caught it in the
act.
Here's the assembly for the loop that calls
WaitForRX():
511: if (
(DWORD)psThreadData == 0x00000001)
02CD1B7B
cmp
esi,ebx
02CD1B7D
jne CommsRXThreadProc+45h
(02cd1b81)
512:
psThreadData->bTerminate = FALSE ;
02CD1B7F
mov dword ptr
[esi],edi
513:
dwNumBytes = WaitForRX(*psThreadData, sNotifyOverlapData);
02CD1B81
lea
eax,[sNotifyOverlapData]
02CD1B84
push eax
02CD1B85
push esi
02CD1B86
call WaitForRX
(02cd1bbb)
02CD1B8B
pop
ecx
It did NOT hit the breakpoint set at lines 511 /
512, so the pointer was still valid when it went into the call.
Here's
WaitForRX(), with the breakpoint I added and it triggered:
DWORD
WaitForRX(COMMS_RX_THREAD_DATA_S& rsThreadData, OVERLAPPED&
rsNotifyOverlapData)
{
BOOL bDone ;
COMSTAT sStatus ;
DWORD dwEvent, dwError, dwDummy, dwNumBytes
;
dwNumBytes = 0
; // Until we have definitely been
notified of something
// being received.
//
JDEBUG
if ( (DWORD)&rsThreadData ==
0x00000001)
dwDummy = 0
; <== Hit breakpoint
here
if
(!::WaitCommEvent(rsThreadData.hPortHandle,
&dwEvent,
&rsNotifyOverlapData)
)
{
As you can
clearly see, it got corrupted on entry to the call! Bearing in mind it will
have gone through this call hundreds of times successfully before it
(apparently) suddenly fails...
I can confirm that the only other place
the structure is referenced by the pointer passed to the comms thread is in
ReceiveBytes(), which doesn't get called until AFTER WaitForRX(), and there
are checks to make sure the pointer isn't going wrong after that - and it is
not. The original structure is not being used beyond when the thread is
created and its address is initially passed, and it is not going out of
scope.
How is this possible?
--
Jason
Teagle
[EMAIL PROTECTED]
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