hello, I have protected a std::queue's access functions, push, pop, size, with boost::mutexes and boost::mutex::scoped_lock in these functions from time to time it crashes in a scoped lock the call stack is this: 0 0x0040f005 boost::detail::win32::interlocked_bit_test_and_set include/boost/thread/win32/thread_primitives.hpp 361 1 0x0040e879 boost::detail::basic_timed_mutex::timed_lock include/boost/thread/win32/basic_timed_mutex.hpp 68 2 0x0040e9d3 boost::detail::basic_timed_mutex::lock include/boost/thread/win32/basic_timed_mutex.hpp 64 3 0x0040b96b boost::unique_lock<boost::mutex>::lock include/boost/thread/locks.hpp 349 4 0x0040b998 unique_lock include/boost/thread/locks.hpp 227 5 0x00403837 MyClass::inboxSize - this is my inboxSize function that uses this code: MyClass::inboxSize () { boost::mutex::scoped_lock scoped_lock(m_inboxMutex); return m_inbox.size(); } and the mutex is declared like this: boost::mutex m_inboxMutex; it crashes at the last pasted line in this function: inline bool interlocked_bit_test_and_set(long* x,long bit) { long const value=1<<bit; long old=*x; and x has this value: 0xababac17 Thanks for the help