CODEWITHSUNDEEP
c++multithreadingrandom
Roy Nieterau
Roy Nieterau

Reputation: 1256

Fast multithreaded random sequence in C++

I need to use random in a multi-threaded loop, but require the same values through each loop independent of which thread is evaluating that cycle.

Without multi-threading I can do:

seed(1)
for (unsigned int i=0; i<100; i++){
     rand()
}

Within the loop each time rand() will be called it will return a new pseudo-random value. Now I want to create the same list multi-threaded.

The main reason is that I need the same sequence of pseudo-random numbers independent of the order of the loop (so more like based on 'i' within the loop).

Note: I've been going through many 'random' and 'multithreading' topics but only found solutions on how to make sure the numbers are always random, not the other way around.

EDIT:

The result should be as if based on a seed a random list is created. And that random list should be used within the loop with index 'i' to get the pseudo-random value. So within the loop the same random number will be at index 'i' based on the seed. (Yet there shouldn't be a single random number same throughout the loop. But the sequence should be the same for each program run. Independent of number of threads or which thread is evaluating a part of the cycle.)

It wouldn't be very efficient to create that list (non-multithreaded) and use that initialized list within the multithreaded loop. Any thoughts on this?

Upvotes: 3

Views: 568

Answers (2)

GHL
GHL

Reputation: 572

You need a counter-based random generator, instead of a congruential one. A good document explaining how they work is here:

http://www.thesalmons.org/john/random123/papers/random123sc11.pdf

Upvotes: 3

Pavel Radzivilovsky
Pavel Radzivilovsky

Reputation: 19104

Use any non-STDC random number generator, with a separately manageable state. I recommend this: http://www.boost.org/doc/libs/1_52_0/doc/html/boost_random.html

Upvotes: 4

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