C++ super fast thread-safe rand function
c++, multithreading, optimization, random
Solution
Problem is that `seedp` variable (and its memory location) is shared among several threads. Processor cores must synchronize their caches each time they access this ever changing value, which hampers performance. The solution is that all threads work with their own `seedp`, and so avoid cache synchronization.
Problem
``` void NetClass::Modulate(vector <synapse> & synapses ) { int size = synapses.size(); int split = 200 * 0.5; for(int w=0; w < size; w++) if(synapses[w].active) synapses[w].rmod = ((rand_r(seedp) % 200 - split ) / 1000.0); } ``` The function `rand_r(seedp)` is seriously bottle-necking my program. Specifically, its slowing me by 3X when run serialy, and 4.4X when run on 16 cores. `rand()` is not an option because its even worse. Is there anything I can do to streamline this? If it will make a difference, I think I can sustain a loss in terms of statistical randomness. Would pre-generating (before execution) a list of random numbers and then loading to the thread stacks be an option?