On 4/9/2011 3:48 AM, Peter Dimov wrote:
Phil Bouchard wrote:
And an overview is available here: http://www.fornux.com/personal/philippe/devel/shifted_ptr/libs/smart_ptr/doc...
Please let me know if anything isn't clear enough.
It's not clear how shifted_ptr detects cyclic blocks of memory with no coding overhead. The methods with which I'm familiar require (a) the ability to enumerate all pointer subobjects in an object and (b) the ability to zero these pointers so as to break the cycles. Without some sort of registry that tracks all pointer instances (overhead on construction/destruction) (a) requires cooperation from the pointee, which shifted_ptr does not seem to demand.
It stacks up all allocations made on the heap to later track within which memory block a shifted_ptr belong to. This is what pool::top() defined in "sh_owned_base_nt.hpp" does. Once a pointer from the stack is reached then the set counter is shared will all of the newly allocated blocks of memory.
It's also not clear how cyclic structures are detected immediately. Doing this typically either requires a scan (collection cycle) on every pointer destruction, or some sort of housekeeping on each construction and copy.
I haven't added diagrams yet but the text of the rationale can be found here: http://www.fornux.com/personal/philippe/devel/shifted_ptr/libs/smart_ptr/doc...
It is also not clear how well does the cyclic collector work when, in parallel, other threads create and destroy references to the objects being currently scanned.
The pools are designed to be used by a multithreaded environment and so is the reference counter base class but the manipulation of set haven't been tested yet. Perhaps a mutex can be added to the set counter if an atomic mechanism isn't found. Thanks, -Phil