I have solved this problem. Please see my post in stack overflow at: http://stackoverflow.com/questions/14692802/boost-threads-in-ios-thread-info... The short answer is that the IOS boost.sh script needs to be modified to use BOOST_SP_USE_SPINLOCK instead of BOOST_SP_USE_PTHREADS. But there are a lot of details involved in getting this to work in IOS which are described in that post. Maybe also a small modification to the boost code in spinlock_gcc_arm.hpp, but I need to verify that a change I made along the way is absolutely necessary.