On Nov 13 15:38, Corinna Vinschen wrote: > On Nov 13 15:25, Bruno Haible wrote: > > Corinna Vinschen wrote: > > > The rand() function would still not use locking but AFAICS that's > > > not actually required by POSIX or ISO C. > > > > Correct. Those who want an MT-safe rand-like function need to use random(), > > not rand().
I took a look into POSIX and I'm a bit puzzled now. From https://pubs.opengroup.org/onlinepubs/9699919799/functions/rand.html RATIONAL The ISO C standard rand() and srand() functions allow per-process ^^^^^ (not requires) pseudo-random streams shared by all threads. Those two functions need not change, but there has to be mutual-exclusion that prevents interference between two threads concurrently accessing the random number generator. Ok, so, *iff* rand/srand share per-process state, then they have to use locking to prevent MT interference. POSIX continues: With regard to rand(), there are two different behaviors that may be wanted in a multi-threaded program: 1. A single per-process sequence of pseudo-random numbers that is shared by all threads that call rand() 2. A different sequence of pseudo-random numbers for each thread that calls rand() ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ I read this as the newlib technique being one way of correctly implementing rand/srand, no? Corinna -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
