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First run – Count was around 70 mp-test ~ # ./a.out tot: 778262873 l1: 2060261465 l2: 2060261465 Aborted Second Run – Count was at 400 mp-test ~ # ./a.out tot: 4033371507 l1: 1314891622 l2: 1314891622 Aborted Third Run – Count was at 130 mp-test ~ # ./a.out tot: 1427405301 l1: 475005228 l2: 475005228 Aborted mp-test ~ # ./a.out tot: 1309167503 l1: 71029242 l2: 71029242 Aborted -Aron From: Alan Hawrylyshen
[mailto:alan@xxxxxxxxxxxx] 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 -- #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. |