Boost C++ Libraries: Ticket #5372: spinlock fails on iPad2

version, component changed; owner set

Trantec@… — Fri, 25 Mar 2011 15:35:33 GMT

owner set to Peter Dimov
version Boost 1.45.0 → Boost 1.41.0
component None → smart_ptr

Peter Dimov — Fri, 25 Mar 2011 17:39:08 GMT

Not good. So the iPad2 version of GCC supports the sync instrinsics? We'll need to enable their use in shared_ptr then - previous GCCs for iPhone didn't have them. How can we detect that the sync intrinsics work?

severity changed

Peter Dimov — Fri, 25 Mar 2011 17:39:44 GMT

severity Problem → Showstopper

Peter Dimov — Sun, 27 Mar 2011 20:17:34 GMT

What is your GCC version, and does it define the predefined macro __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4?

anonymous — Tue, 29 Mar 2011 07:37:59 GMT

Sorry for the delayed answer.

I think the marko "_GLIBCXX_ATOMIC_BUILTINS" has to be defined. At least in the settings of my project it is. (see link: http://iphone.galloway.me.uk/2010/05/iphone-sdk-bug-hunting-gcc-atomic-builtins/).

I'm using Gcc 4.2, it seams this is the first version to support atomic builtins...

Peter Dimov — Tue, 29 Mar 2011 13:23:04 GMT

Thanks, this is useful info. Can you please run the following tests for me (each of those is independent of the others):

Modify spinlock_gcc_arm.hpp to contain memory barrier instructions as follows:

change "swp %0, %1, [%2]": in try_lock to "swp %0, %1, [%2]\n\tdmb":
change __asm__ __volatile__( "" ::: "memory" ); in unlock to __asm__ __volatile__( "dmb" ::: "memory" );

and see if this fixes things (this will need to be compiled in ARMv7 mode)?

Modify spinlock.hpp to use spinlock_sync.hpp instead of spinlock_gcc_arm.hpp and see if this fixes things?

Modify sp_counted_base.hpp to use sp_counted_base_sync.hpp instead of sp_counted_base_spin.hpp and see if this fixes shared_ptr? (In this case the spinlock will be still broken but we'll apply 1 or 2 to it as well.)

anonymous — Mon, 13 Jun 2011 22:14:19 GMT

What came of this?

Peter Dimov — Tue, 14 Jun 2011 11:00:45 GMT

Nothing, I'm afraid. I'm still awaiting answers to my questions above. I don't have access to an iPad 2 (or another dual core ARM device) development environment myself.

anonymous — Tue, 14 Jun 2011 18:58:56 GMT

We have verified that there is a genuine spinlock bug on both the iPad2 and Motorola Atrix. Our workaround was to use the pthread-based implementation. Once we get past our current shared-pointer-induced crisis, we will test your patch and report the results.

Phil Endecott — Tue, 21 Jun 2011 14:27:21 GMT

As described in this thread:

http://thread.gmane.org/gmane.comp.lib.boost.devel/217094/focus=217107

I'm using a shared_ptr implementation based on boost.atomic; I've just posted that code in ticket #5625. This seems to be working reliably in a couple of iPad 2 apps, and should be much more performant than your current pthread workaround.

anonymous — Thu, 30 Jun 2011 00:12:41 GMT

Please, someone get this man an iPad2! :)

anonymous — Wed, 13 Jul 2011 23:37:53 GMT

I'm confused. I cannot reproduce this error on my iPad2. The testcode outputs the expected results. Tested with 1.46.1 & 1.47. What am I doing wrong?

marcus.alanen@… — Wed, 05 Oct 2011 13:14:25 GMT

Hello,

we've also had crashing bugs on a multithreaded game with shared_ptrs on iPad2 - very mysterious of course, and not easily testable.

I tried adding dmb instructions as per suggestion 1 above by pdimov, and after some casual testing so far we haven't had any issues. However, this is of course no guarantee, but I hope this at least gives you something.

Best Regards,

Marcus Alanen

Tribeflame

Peter Dimov — Mon, 07 Nov 2011 17:50:34 GMT

(In [75389]) Add ARM memory barriers. Refs #5372.

status changed

Peter Dimov — Mon, 07 Nov 2011 18:27:09 GMT

status new → assigned

anonymous — Tue, 08 Nov 2011 13:43:32 GMT

instead of retaining the swp instruction (which is deprecated with ARMv7 also because of performance problems), wouldn't it be better to use the gcc builtins where available (resp. the corresponding ldrex/strex assembler instructions where not)?

status changed; resolution set

Peter Dimov — Wed, 30 Nov 2011 17:49:45 GMT

status assigned → closed
resolution → fixed

(In [75753]) Merge [75389] to release. Fixes #5372.

shreyas.bme@… — Tue, 31 Jan 2012 21:16:24 GMT

Hi,

I am getting following error for iPhone. I am using Boost 1_45_0

I will appreciate for your reply.

Following is error logs...from Xcode

ld: bad codegen, pointer diff in boost::signals::connection::connection(boost::signals::connection const&)to global weak symbol boost::detail::spinlock_pool<1>::pool_ for architecture armv7 collect2: ld returned 1 exit status Command /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/g++-4.2 failed with exit code 1