Re: sigsev while creating new gdd in multiple threads

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hi Bruno,

From what I can see in the macro definition of gdd_NEWDEL_NEW(gdd) in 
gddNewDel.h, the gddScalar::new() operator is not fully thread safe. 
Initialization of the freelist is not protected. Thus, calling gdd*::new() for 
the first time in two different threads may crash. Maybe using gdd*::new() the 
first time while still in single threaded context may cure the problem.

Dirk


Bruno Coudoin wrote:
> Hi,
>
> Tonight I found something odd. I am perhaps doing something wrong but
> after several test the results were consistant.
>
> I have a multithreaded application, at startup each thread creates
> several gdd. It ends up frequently in the following SIGSEGV:
>   Program received signal SIGSEGV, Segmentation fault.
>   [Switching to Thread 0x98a35b90 (LWP 1020)]
>   0x00f2b2b8 in gdd::operator new (size=44) at ../gdd.cc:26
>   26      gdd_NEWDEL_NEW(gdd)
>
> My code to create the gdd is as simple as:
>   gdd *pDD;
>   pDD = new gddScalar ( gddAppType_value, aitEnumInt32 );
>
> It seems like my program crashes at startup but if it passed the first
> gdd creation of each threads, it becomes stable after that. More threads
> I have, more chance I have to see the crash.
>
> My configuration:
> Epics 3.14.10
> CentOS 5.3
> Multi core processor.
>
> Has anybody ever seen this issue? I'll try to dig further tomorrow, if
> someone has ideas on workarounds or tests to do to refine the issue,
> your welcome.
>
> Bruno.

--
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182