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 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.