<Oliver.Kowalke@qimonda.com> wrote in news:B1EAFF2DAE7658488B631F25813CD91FD388B7@drsse602.eu.infineon.com:
Hello Andy,
I am not very happy with the create_v1() function in guid_v3.zip. Really it just pretends to implement the specification correctly. Because MAC-address of the nic isn't used?
Yes, because the MAC-address is not used which increases the probability of duplicates. Also my implementation does not use stable storage and this is the least desirable implementation, because it will increase the frequency of creation of new clock sequence numbers, which increases the probability of duplicates. < snip >
How is your implementation of uuid v4 unique in space (guids genereated on several computers at the same time) and time?
My implementation of version 4 (random-number-based) guids may not be unique in space and time. It is based on boost::mt19937 to generate random numbers and it is seeded with std::time(0). Cryptographic-quality random numbers would reduce the probability of repeated values. Using version 5 (name-based) guid can be used to ensure that guids are unique in space (guids generated on several computers at the same time) and time. Generate a guid for each computer as the namespace_guid and pass a counter as the name to the create function. example: (not tested or compiled) const static guid computer_namespace_guid("{00000000-0000-0000-0000-000000000000}"); // or some other guid that never changes guid generate_guid() { // get unique string for computer // could be mac address const char* computer_name = get_unique_computer_name(); const static guid namespace_guid = guid::create(computer_namespace_guid, computer_name, strlen(computer_name)); static int count = 0; guid result = guid::create(namespace_guid, static_cast<char*>(&count), 4); ++count; return result; }
Regards, Oliver _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
Andy.