[boost] thread_specific_ptr suggestion

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2004-05-15 17:35:29

thread_specific_ptr<T> is the thread local data storage mechanism of 
the excellent (thanks William!) boost threads library.  
thread_specific_ptr<T> isn't capable of supporting custom deleters for 
good reason.  The deleter function must be a real function (not a 
functor) so as to work well with various OS level threading api's (like 
Posix threads).  So the pointer passed into a thread_specific_ptr<T> 
(via reset) must be free-able with delete.

thread_specific_ptr<T> could offer a custom deleter constrained to be a 
function pointer instead of a more general deleter policy (functor), 
but that seems like it would be of limited functionality and frankly 
just not much fun in a C++ environment.

However, there is one case where another deleter policy is common 
enough to warrant special attention:  delete [].

So I suggest a partial specialization for thread_specific_ptr:

template <class T>
class thread_specific_ptr<T[]>
{
public:
     thread_specific_ptr();
     ~thread_specific_ptr();

     T* get() const;
     T& operator[](std::size_t i) const;
     T* release();
     void reset(T* p = 0);

private:
     thread_specific_ptr(const thread_specific_ptr&);
     thread_specific_ptr& operator=(const thread_specific_ptr&);
};

In this case, any pointers owned by thread_specific_ptr<T[]> must be 
free-able with delete [].

thread_specific_ptr<int>   value;
thread_specific_ptr<int[]> array_value;

void foo()
{
     value.reset(new int);
     array_value.reset(new int [3]);
     ...
}

-Howard