On Fri, Jun 22, 2012 at 03:38:14PM +0700, Randi Botse wrote: > Hi Nicholas, > > So sorry, I was mean clock_gettime() not nanosleep(), my bad. The > unique ID must be different in all proces, so no duplicated ID in > entire process. > > And here the ID should be generated: > > struct timespec ts; > clock_gettime(CLOCK_REALTIME, &ts); > unsigned long uid = ts.tv_sec + ts.tv_nsec; > > Does your reply also covering this? > > Thanks, > > On 6/22/12, Nicholas Mc Guire <der.herr@xxxxxxx> wrote: > > On Fri, 22 Jun 2012, Randi Botse wrote: > > > >> Hi All, > >> > >> In nanosecond precision, if I have multiple processes run nanosleep(), > >> how possbile they will get the same struct timespec value? both the > >> tv_sec and tv_nsec value. Of course the tv_sec (second) is most > >> possible, but how about the tv_nsec (nanosecond)? > >> > >> I wan't to create a simple stupid unique id or something like that, > >> but with without too much effort. The unique id will be tv_sec + > >> tv_nsec. > >> > > while it is highly unlikely that they get the same tv_nsec it is not > > impossible so it will not make for a good ID. The problem with such > > an ID is simply that if you have a collision then it will be very hard > > to debug this situation. Even worse this solution would not be portable > > at all - it even could work on one box (e.g. a UP system where the > > processes never execute physically concurrent) and fail on a MP in > > rare cases - portability to other OS would also be very shaky at the > > concept level (even if the API were pure POSIX). > > > > there are unique objects available to any process, pid, address (if > > address space randomization is enabled), /dev/random|/dev/urandom > > fetching a long long from there is far more reliable than generating > > a shaky long long from tv_nsecs (where the upper bits will almost > > surely match). > > > > let us know what you need it for and it is easiert to give some > > suggestions. > > > > thx! > > hofrat > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html Hi Why don't you use universally unique identifier (UUID)[1]? I was invented and standardized to deal with cases like yours. You can find more information how to use UUID in your software form man uuid [2] [1] http://en.wikipedia.org/wiki/Universally_unique_identifier [2] http://linux.die.net/man/3/uuid Best wishes Vladimir Murzin -- To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
