a custom allocator for the tbb::concurrent_unordered_map

[Andrew_Stepanchuk]

I am trying to provide my allocator for the tbb::concurrent_unordered_map to do a custom action on the value, but the destroy method of the allocator receives a pointer of the flist_iterator type which has the protected my_node_ptr variable. So I can not access it.

What is the right way to provide a custom action on the destroy? (besides modifying the tbb source code)

Note: the value is a pointer and I can not wrap it into a struct as value, I need to have my allocator.

[Christophe_H_Intel]

Hello, Andrew,

The simplest thing I could suggest is to walk the list before destruction, freeing the pointed-to memory.  I think that is what you'd have to do if it was a std::vector of pointers, or other standard library container.

Do I understand your description right?  You are asking if there is a way to insert pointers you have allocated into a concurrent_unordered_map, and when the map is destroyed, have all the pointers you inserted freed first by the map destructor?

Regards,
Chris

[Andrew_Stepanchuk]

Hi Chris,

Yes, when the clear method is called, I need to deallocate all values. And I am trying to avoid a redundant walk since the concurrent_unordered_map goes through all values anyway. I have a lot of stuff in memory so I am trying to make it more efficient.

[Andrew_Stepanchuk]

Here is how to provide a custom action on the destroy:

[cpp]template<typename T>
struct myalloc: tbb::tbb_allocator<T> {
   template<typename U>
   struct rebind {
      typedef tbb::tbb_allocator<U>other; // OK
      // typedef myalloc<U> other; // ERROR
   };
   myalloc() throw() {}
   myalloc(const myalloc&) throw() {}
   template<typename U> myalloc(const myalloc<U>&) throw() {}
   void destroy(pointer p) {
      delete (**p).second; // custom action
      p->~value_type();
   }
};[cpp]