title: Boost.Thread threads not starting on the iPhone/iPad in release builds
body: <p>We're writing an iPad app with quite a lot of background processing all of which is written in a set of C++ libraries. These libraries work fine on Linux, Mac and Windows but on the iPad they only work in debug builds.</p>
  
  <p>In release builds, it looks like when the first sub-thread is being spun up it either never actually starts, or it doesn't get far enough in its processing to allow the main thread to continue (it isn't very obvious from the debugger if the thread is actually starting or not due to the normal problem of using break points in release builds).</p>
  
  <p>Looking in the debugger the main thread sits in <code>boost::thread::start_thread</code> (actually inside <code>boost::detail::yield</code> within <code>boost::detail::spin_lock::lock</code>).</p>
  
  <p>The CPU isn't at 100% so it doesn't appear that the spin lock is starving the creation of the new thread.</p>
  
  <p>We've tried both Boost 1.42 and Boost 1.44 and they both behave the same way. Both iOS 3.2 and 4.2 both fail with release builds.</p>
  
  <p>What are we likely doing wrong, or is this a known not-working configuration?</p>