Condition.Wait with a mutex instead of lock can be mysterious

[Trey Van Riper <fleeb.fantastique@…>]

This code correctly fails to compile: #include <boost/interprocess/sync/named_condition.hpp> #include <boost/interprocess/sync/named_mutex.hpp>

int _tmain(int argc, _TCHAR* argv[]) {

boost::interprocess::named_mutex mutex( boost::interprocess::open_or_create, "test" ); boost::interprocess::named_condition condition( boost::interprocess::open_or_create, "test" ); condition.wait( mutex ); return 0;

}

The resulting compile error (at least on VC++ 2010) is a tad mysterious:

1>c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\shm\named_condition.hpp(204): error C2248: 'boost::interprocess::interprocess_mutex::mutex' : cannot access private member declared in class 'boost::interprocess::interprocess_mutex' 1> c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\interprocess_mutex.hpp(117) : see declaration of 'boost::interprocess::interprocess_mutex::mutex' 1> c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\interprocess_mutex.hpp(67) : see declaration of 'boost::interprocess::interprocess_mutex' 1> c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\shm\named_condition.hpp(204) : while compiling class template member function 'boost::interprocess::ipcdetail::shm_named_condition::lock_wrapper<Lock>::mutex_type *boost::interprocess::ipcdetail::shm_named_condition::lock_wrapper<Lock>::mutex(void) const' 1> with 1> [ 1> Lock=boost::interprocess::named_mutex 1> ] 1> c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\shm\named_condition.hpp(342) : see reference to class template instantiation 'boost::interprocess::ipcdetail::shm_named_condition::lock_wrapper<Lock>' being compiled 1> with 1> [ 1> Lock=boost::interprocess::named_mutex 1> ] 1> c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\named_condition.hpp(156) : see reference to function template instantiation 'void boost::interprocess::ipcdetail::shm_named_condition::wait<L>(L &)' being compiled 1> with 1> [ 1> L=boost::interprocess::named_mutex 1> ] 1> c:\code\projects\testinterprocess\testinterprocess\testinterprocess.cpp(10) : see reference to function template instantiation 'void boost::interprocess::named_condition::wait<boost::interprocess::named_mutex>(L &)' being compiled 1> with 1> [ 1> L=boost::interprocess::named_mutex 1> ] 1>c:\code\sdks\boost\include\boost-1_50\boost\interprocess\sync\shm\named_condition.hpp(204): error C2064: term does not evaluate to a function taking 0 arguments

It is not obvious that the problem involves the use of a Mutex instead of a ScopedLock or the like. While the example code makes this clear, if you examine only the documentation, this detail might be confusing.

Recommend adding a concept check to help guide someone towards using a lock instead of a mutex.