[1.7.0-60] crash on exit on c++ program (octave)

Dave Korn dave.korn.cygwin@googlemail.com
Fri Aug 21 15:41:00 GMT 2009

Christopher Faylor wrote:
> On Fri, Aug 21, 2009 at 10:57:42AM +0200, Corinna Vinschen wrote:
>> On Aug 20 21:12, Dave Korn wrote:
>>> Dave Korn wrote:
>>>>   We should probably make running the dtors idempotent, or unlink each dll
>>>> from the dll_list as we go.  I need to think about this for a little while,
>>>> more later.
>>>   The solution could be as simple as this.  Just don't call dtors for dlopen'd
>>> DLLs when we run the global dll dtors.  If the application dlcloses them,
>>> their dtors get run then.  If it doesn't, they'll be run much later when the
>>> dlopen'd module receives DLL_PROCESS_DETACH as everything is being closed.
>>> Only thing I'm wondering about is if we shouldn't forcibly dlclose any
>>> left-over modules as part of the dtors sequence so that they run before the
>>> newlib i/o shutdown.  Anyone got an opinion?
>> I think the dlclose call should be enforced for left-over modules.  We
>> can use the below as temporary patch to avoid the crash for now.
> I did some debugging on this last night.  I made what seemed to be an
> obvious fix of running the destructors before the dll was unloaded and
> still got a segv.  I didn't have time to track it down further but I
> don't like the fact that destructors for dlopened modules cause a crash.
> Dave's change seems wrong to me.  I don't know why we'd avoid running
> destructors.  We should just not run them after the module has been
> unloaded.

  That isn't the problem.  The dtors were being run *twice*.  The program
exits, and all the atexit calls get run; first the program's dtors, then
dll_global_dtors gets called.  That works its way down the dll list, calling
all their dtors.  First it calls the dtors of the dlopen'd modules, which were
added to the end most recently.  Then it calls the dtors of some of the
statically loaded DLLs, one of which calls dlclose.  dlclose calls
FreeLibrary, the DLL gets a PROCESS_DETACH notification, and calls its dtors
for a second time.


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