This feature is deprecated and will be removed in the future.
By default various implementations of mutexes are not copyable or movable (Prior to Intel® Threading Building Blocks 4.3 copying was possible for some of the mutex classes). If the macro TBB_DEPRECATED_MUTEX_COPYING is non-zero, it's possible to call assigment operators and copy constructors on mutexes.
C++11 forbids mutex types to be copyable or movable, so the old behavior is not compatible with the C++ standard.
Copying of a locked mutex, as well as copying concurrently with other operations on the same mutex, leads to undefined behavior.