Re: [Boost-users] [interprocess] another newbie question: clean-up

Hi, Wolfgang Hottgenroth wrote:

Hi, [snip]

To put pair into the map I wrote:

typedef boost::interprocess::allocator ShmemStringAllocator; typedef boost::interprocess::basic_string MyString;

MyString key(segment.get_segment_manager()); MyString value(segment.get_segment_manager());

key = "key1"; value = "value1";

mymap->insert(std::pair(key, value));

(For the complete code see http://www.hottis.de/boost/strings/. Thanks.)

What I'm wondering is: will the memory required for key and value be freed automatically in the writing process (put.C)?

If you refer to the local "key" and "value" variables, the string objects (the class that contains a pointer to a dynamically allocated object) are allocated in your process' stack, but the dynamically allocated buffers holding "key1" and "value1" are allocated in shared memory. When "key" and "value" go out of scope, memory is automatically reclaimed. Just like std::string. The difference is that std::string allocates the internal buffer calling std::allocator::allocate (that is, operator new[]), whereas boost::interprocess::allocator will allocate the string from shared memory (using boost::interprocess::allocator::allocate). But anyway, when the object is destroyed, memory is freed.

When I like to erase an element from the map, do I need to do more than just calling mymap->erase(key)?

No. That's all. All the dynamic memory from the strings (allocated in the shared memory segment) is also freed.

And finally when I'm done and like to remove the whole map, is more required than segment.destroy<MyMap>("MyMap")? Will all the MyString's in the map go too?

Yes. All will be automatically freed.

Furthermore: is it possible to use a map in shared memory as an associative array and write:

MyString value = (*mymap)[key];

It doesn't compile for me.

The problem when using operator[], is that the mapped type must be default constructible. And boost::interprocess::basic_string, needs the allocator argument. You will need to use insert, sorry.

Thanks, Wolfgang

Regards, Ion