#12 Thread safety

[Alessandro Ranellucci]

Hello!
Am I right in assuming OpenGL::Array is not thread safe? It looks like the underlying data storage is not duplicated when object is cloned, but DESTROY {} tries to free it twice.

The following workaround should be enough:
*OpenGL::Array::CLONE_SKIP = sub { 1 };

[Chris Marshall]

I don't see a duplicate free() in the DESTROY() call for OpenGL::Array objects. This is for the current release version 0.6703. It is possible that the code is not thread safe but I don't think there are tests for that. Could you give a link/line number or more detail for what you see?

Thanks,
Chris

[Alessandro Ranellucci]

Oh, it's very easy to reproduce:

my $array = OpenGL::Array->new(4, GL_FLOAT);
threads->create(sub { $array })->join;

perl(65121,0x313540) malloc: *** error for object 0x544540: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

Double free() happens because both threads call $array->DESTROY().
See http://perldoc.perl.org/perlmod.html#Making-your-module-threadsafe
I think a CLONE_SKIP { 1 } would be the best choice for OpenGL::Array.

[Chris Marshall]

Thanks, I see what you mean. It is definitely not
thread safe then. I'll add that work around and info
to the release.

-chm

On Sat, May 3, 2014 at 5:17 AM, Alessandro Ranellucci
alexrj@users.sf.netwrote:

Oh, it's very easy to reproduce:

my $array = OpenGL::Array->new(4, GL_FLOAT);
threads->create(sub { $array })->join;

perl(65121,0x313540) malloc:
* error for object 0x544540: pointer being freed was not allocated * set
a breakpoint in malloc_error_break to debug

Double free() happens because both threads call $array->DESTROY().
See http://perldoc.perl.org/perlmod.html#Making-your-module-threadsafe
I think a CLONE_SKIP { 1 } would be the best choice for OpenGL::Array.

---

• [bugs:#12] http://sourceforge.net/p/pogl/bugs/12/ Thread safety*

Status: open
Group: POGL 0.xx
Created: Fri May 02, 2014 11:12 AM UTC by Alessandro Ranellucci
Last Updated: Fri May 02, 2014 09:59 PM UTC
Owner: nobody

Hello!
Am I right in assuming OpenGL::Array is not thread safe? It looks like the
underlying data storage is not duplicated when object is cloned, but
DESTROY {} tries to free it twice.

The following workaround should be enough:
*OpenGL::Array::CLONE_SKIP = sub { 1 };

---

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[Alessandro Ranellucci]

Hello Chris, any update on this?
Thank you!

[Chris Marshall]

Where does the fix line go? Patches against git welcome.

[Chris Marshall]

It looks like this has already been applied to git master.
Could you please verify that everything builds, runs, and
looks ok and I'll push a new CPAN release as soon as I get
confirmation from you.

Thanks,
Chris