| I am still quite tempted to prove what the failure is with a minimal test driver. I fear that it might be something slightly more insidious. So, once we can cause this to happen at-will, we can address the appropriate root cause. Is this something that can be checked easily? Anyone?
I have a test driver that fails on a dual core intel platform, gcc 4.0.1, Mac OS X 10.5.2 This will fail around the 100 mark in the progress output (but I have waited much longer). Let it run for a while and see. This will abort when two successive calls to random() match.
I would expect this to be unlikely, but should we check this on a single processor / single core system? Does it happen more often on dual core or SMP systems? Aron - can you try this on your platform? Please run it a LOT and see if the time-to-run varies greatly or if it fails reliably.
Thanks Alan
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#include <stdio.h> #include <time.h> #include <unistd.h> #include <stdlib.h> #include <string.h>
int main() { unsigned long long t = 0; unsigned long l1 = (unsigned long)random();
srandom(time(0));
unsigned long l2 = 0UL; while (3) {
l2 = (unsigned long)random();
if ( l1 == l2 ){ printf("tot: %llu\nl1: %lu\nl2: %lu\n",t,l1,l2); abort(); } l1 = l2; t++; const int modulator = 10000000L; if (!(t % modulator)) { printf("%llu...\r",(t/modulator)); fflush(stdout); } }
return 0; }
Alan On 19-Mar-08, at 15:56 , Aron Rosenberg wrote: The only thing that I could think of is to use the new random_r and srand_r functions instead of random and srand. The glibc _r ones force the application to keep the “seed” value which might make it immune to the caching problem. The issue with this approach was that the entire Random() class is static although you could just add a class wide static variable to hold the new userland data.
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