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
