Re: [Boost-users] [shared_ptr] hangs on iPhone

Subject: Re: [Boost-users] [shared_ptr] hangs on iPhone
From: Peter Dimov (pdimov_at_[hidden])
Date: 2009-11-26 15:04:04

Igor R wrote:
> Thanks a lot for your answer, you pointed me in the direction I didn't
> think of: __thumb__! Actually, my project was compiled with Thumb
> switched on - which is default in XCode. On the other hand, boost
> libraries was built with their default compiler switches for this
> platform, as defined in boost.build/bjam configuration (probably,
> thumb off?).
> Anyway, now I switched off Thumb in my project settings, and
> everything began to move as expected!

Thanks for tracking this down.

>> Is your application multithreaded, or does even a simple uncontended
>> use of boost::detail::spinlock or boost::detail::spinlock_pool fail?
>
> My application is multithreaded, but spinlock_pool was hanging in
> absolutely "uncontended" places - like in regex, which I use in 1
> thread only.
>
> I still don't understand why it behaved like this - afterall, if
> thumb-enabled code doesn't support such a spinlock, it should crash,
> and if it does support, it should work...

The ARM-specific implementation is only used when __thumb__ is not defined:

#if defined(__GNUC__) && defined( __arm__ ) && !defined( __thumb__ )
#  include <boost/smart_ptr/detail/spinlock_gcc_arm.hpp>

because Thumb doesn't support the swp instruction and spinlock_gcc_arm 
doesn't compile. This causes an ABI mismatch when Thumb and non-Thumb files 
are linked together; the inlined code is trying to lock a spinlock that 
doesn't exist.