fork.c

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

/* MB of memory to allocate */
#define MB 100
/* How many processes to spawn */
#define FORKS 50
/* How many random elements to change in the child process */
#define NUMRANDS 100000
/* Change sequential or random elements in the child process */
#define SEQ 0


int main() {
	int forks = 100;
	int i, j;
	int *baba;
	int f;
	int s = (MB*1024*1024)/sizeof(int);
	baba = malloc(s*sizeof(int));
	printf("Start loop in parent\n");
	for(i=0; i<s; ++i) {
		baba[i] = rand();
	}
	printf("End   loop in child\n");
	forks = FORKS;
	while(forks--) {
		f = fork();
		if (0 == f) {
			printf("Start loop in child %d\n", getpid());
			for(i=0; i<NUMRANDS; ++i) {
				if (SEQ)
					baba[i%s] = rand();
				else
					baba[rand()%s] = rand();
			}
			printf("End   loop in child %d\n", getpid());
			exit(0);
		} else if ( -1 == f) {
			printf("Error forking #%d\n", forks);
		} else {
			printf("Forked %d\n", forks);
		}
	}

	while (1) {
		int status;
		pid_t done = wait(&status);
		if (done == -1) {
			if (errno == ECHILD) break; // no more child processes
		} else {
			if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
				printf("Failed wait: %d\n", done);
				exit(1);
			}
		}
	}
	free(baba);
}