Re: Cygwin 1.7: Concurrency Issue with Shared State Initialization

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Fri, Mar 12, 2010 at 04:48:14PM +0100, Schmidt, Oliver wrote:
>Hi,
>
>> Does the patch help?
>
>As the issue is sporadic it's not that easy to come up with a conclusive
>answer...
>
>I downloaded http://cygwin.com/snapshots/cygwin1-20100309.dll.bz2, 
>unpacked and renamed the DLL and used it as drop-in replacement to the
>1.7.1 DLL.
>
>I experienced three times by now the effect that echo.exe "hangs" without
>using significant CPU time.

Is echo being run under a bash shell?  From the command prompt?  In a
.bat file?  Repeatedly in a loop?

>Attaching a MSVC debugger I could only find
>out that in all three cases the executable stays in this endless loop:
>
>7D6373D2  cmp         dword ptr ds:[7D6A0220h],edi 
>7D6373D8  jne         7D628061 
>7D6373DE  lea         eax,[ebp-28h] 
>7D6373E1  push        eax  
>7D6373E2  push        ebx  
>7D6373E3  call        7D61CCB1 
>7D6373E8  cmp         eax,ebx 
>7D6373EA  jge         7D6373D2 
>
>I'm sort of reluctant to present this information this way as I'm afraid
>I'm to give someone a bum steer. However I haven't had this effect so far
>with with the 1.7.1 DLL so it would be at least one possible explanation
>that the patch has a bug showing up in the very sporadic case it is
>supposed to fix.

If you also grab cygwin1-*.dbg.bz2 and uncompress it next to cygwin1.dll
as "cygwin1.dbg" you should be able to attach to a hung process with gdb
and get a backtrace with symbols:

c:\>c:\cygwin\bin\gdb /bin/echo.exe <pid>
(gdb) bt

That may provide more details about where the process is hanging.

Also if you can capture the first few screens after typing:

(gdb) x/80x $esp
(gdb) <just hit enter here>

that would be useful.

cgf

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