Question

Today we were discussing how long Garbage Collection breaks needs. And were wondering how long it would take to simply wipe 1 Gigabyte of memory. What would it take?

Answer 1

On my machine, about one second:

#include <stdlib.h>
#include <stdio.h>


const long long int NUM =  1024*1024*1024/8;

int main(void) {
    long long int* ptr = malloc(NUM  * sizeof ptr);
    printf("Gigabytes: %lld\n",NUM * sizeof ptr / 1024 / 1024 / 1024);
    for(int i=0;i<NUM;i++) {
        ptr[i]=1l;
    }
}

I then run the following (which unwillingly measures the allocation time, too:

$ gcc -O3 -std=c99 mem.c -o mem
$ time ./mem
Gigabytes: 1

real    0m1.056s
user    0m0.205s
sys  0m0.845s