Ben Pope wrote:
On Tuesday, April 21, 2015 06:42 PM, Ben Pope wrote:
89 SUMMARY: ThreadSanitizer: data race /home/ben/development/boost/test/build/boost_root/status/../boost/smart_ptr/detail/shared_count.hpp:449:49 in boost::detail::shared_count::shared_count(boost::detail::shared_count const&)
I've just been looking at this one, ...
I took a quick look at all the smart_ptr issues, and all of them seem to be in Boost.Thread; essentially ThreadSanitizer claims that Boost.Thread causes a race on a shared_ptr variable (although the actual report varies.)
... essentially it seems to boil down to:
#include <atomic> #include <thread> #include <cstdint>
typedef _Atomic( std::int_least32_t ) atomic_int_least32_t;
inline void atomic_increment( atomic_int_least32_t * pw ) { __c11_atomic_fetch_add( pw, 1, __ATOMIC_RELAXED ); }
int main() { atomic_int_least32_t use_count_; std::thread t ([&](){ atomic_increment(&use_count_); }); __c11_atomic_init( &use_count_, 1 ); t.join(); }
It's not possible to achieve this by using shared_ptr (without contortions), as the constructor initializes use_count_ to 1 and you can't (ordinarily) make a thread addref a shared_ptr variable that hasn't been constructed yet. A likelier explanation would have been that ThreadSanitizer is in some way confused by the way Boost.Thread creates threads, but in fact, stack traces show pthread_create, so I've no idea.