Processes in Linux: Getting every child process to sleep a Random number of seconds

Question

I would like to make a variable (that belongs to a process) get a new random value, each time the new process starts.

I need this random generation to make every process created sleep a random number of seconds. At the beginning of the program I used srand(time(NULL)) , and in the function that the process would run I used

int sleeptime = rand() % 16 + 5; //that's because I need values from 5 to 20 int sleeptime = rand() % 16 + 5; //that's because I need values from 5 to 20 .

I've tried to implement such a thing, but I saw that for every process the value of the variable is the same.

I think that if I took as argument for srand(..) the current time in milliseconds (time at which the respective process begins) I would get the random values. The problem is I didn't find any information for this. The only thing suggested on different pages is the well known: srand(time(NULL)); (where time(NULL) returns the current time in seconds).

Can you, please, suggest me some way to implement this? Thank you in advance.

Answer 1

If you're on linux, you also seed the PRNG by reading from /dev/random . Something like this:

void seedprng() {
    unsigned i;
    FILE* f = open("/dev/random", "rb");
    if (f) {
        fread(&i, sizeof(i), 1, f);
        fclose(f);
        }
    else{
        printf("falling back to time seeding\n");
        i = (unsigned)time(NULL);
        }
    srand(&i)
    }