# Concurrent Operations¶

The following table provides additional information on the members of this template class.

Member, Description

reference local()

If there is no current element corresponding to the current thread, then this method constructs a new element. A new element is copy-constructed if an exemplar was provided to the constructor for *this, otherwise a new element is default constructed. See Caution below.

Returns: A reference to the element of *this that corresponds to the current thread.

reference local( bool& exists )

Similar to local(), except that exists is set to true if an element was already present for the current thread; false otherwise. See Caution below.

size_type size() const

Returns: The number of elements in

*this. The value is equal to the number of distinct threads that have called local() after *this was constructed or most recently cleared. See Caution below.

bool empty() const

Returns: size()==0

Caution

The OS-specific value returned by tbb::this_tbb_thread::get_id() is used to identify threads, and is not guaranteed to be unique except for the life of the thread. A newly created thread may get an OS-specific ID equal to that of an already destroyed thread. The number of elements of the enumerable_thread_specific may therefore be less than the number of actual distinct threads that have called local(), and the element returned by the first reference by a thread to the enumerable_thread_specific may not be newly-constructed.