C89：具有rand_r（）的多线程随机值

Question

So, I was curious how someone could get random values across multiple threads with the rand_r command. If I used time(NULL) for the seed everyone ends up with the sam seed because the threads are created so close together. There actions are all based on that random seed, so all the threads remain identical for the remainder of my program. How would one get [ USING RAND_R(*int seed) ] a random number that differed across all threads?

Thanks in advance.

Answer 1

The man page for rand_r on Ubuntu Linux 14.04 suggests:

The value pointed to by the seedp argument of rand_r() provides only a very small amount of state, so this function will be a weak pseudo-random generator. Try drand48_r(3) instead.

Answer 2

您可以使用arc4random为每个线程生成种子值。