On 09/21/07 11:26, Achilleas Margaritis wrote:
O/H Larry Evans έγραψε:
On 09/21/07 04:14, Achilleas Margaritis wrote:
O/H Kim Barrett έγραψε:
At 2:06 AM +0300 9/21/07, Achilleas Margaritis wrote:
I thought std containers use the allocator::pointer type for their pointers. Unfortunately, not necessarily. They're permitted to bypass that and use T* directly. Ion Gaztañaga ran into this when trying to put containers into shared memory for boost.interprocess.
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The collector offers the possibility of customizing the scanning procedure (the procedure which scans a block for pointers) through the class gc_traits<T>. So if there is a data structure where gc_ptr<T> can not be used, a custom scan routine especially coded for the data structure in question can solve the problem. Given the following:
std::list<gc_ptr<Node> > node_list;
where Node is defined in cppgc/src/main.cpp, then no gc_ptr's within node_list would be registered as root pointers; so, wouldn't any Nodes of the gc_ptr's pushed into node_list be collected? I guess I don't understand how a customized scanner would help. Sure, once it's known that node_list contains gc_ptr's, the scanner could be called, but the collector first needs to be notified of that fact.
Am I missing something.
You have to define the appropriate allocator (in this case, gc_allocator<Node>) for the std::list to get its member pointers registered with the collector. gc_allocator<T> defines its pointer as
I thought the user-defined scanner was supposed to overcome this limitation of the stl implementations. At least that what I *thought* you were implying by:
The collector offers the possibility of customizing the scanning procedure (the procedure which scans a block for pointers) through the class gc_traits<T>. So if there is a data structure where gc_ptr<T> can not be used, a custom scan routine especially coded for the data structure in question can solve the problem.
So... are you saying the UDS(User Defined Scanner) cannot overcome the "flawed" stl container use of raw pointer instead of allocator<T>::pointer?
gc_ptr<T>:
std::list<gc_ptr<Node>, gc_allocator<gc_ptr<Node> > > node_list;
Although I made the allocator, it does not work with the VC8 STL or the mingw STL, for the reason mentioned above (STL implementors choosing T* over allocator::pointer).
Is there an STL implementation without this problem? perhaps STLPort? I have to try it myself, but if anyone knows, please tell me.
Wouldn't it be pretty easy to modify the _list template in cppgc.hpp to take a new allocator template parameter and then modify the pointers in _list to use this instead of raw pointers? That way you could easily test to see if future (the ones required to use allocator::pointer) stl containers could be used. You could modify the main_stl I announced in my previous post to do this.