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Using fork() to create a child process
The fork() function is the primitive for creating a child process that can does something in parallel with the main process
After a fork() the main process splits in two parallel process: a parent and a child processes. Both ot them see the fork() return code,
but with different values: it returns 0 in the child process and the child's process ID in the parent process.
If process creation failed, fork returns a value of -1 in the parent process.
This easy example shows how to use the fork() function to create a child process that turn on the red led DL1, wait 7 seconds, turn off the led and die while the
main process counts from 10 to 0 seconds:.
| fork1.c  |
#include "sys/types.h"
#include "sys/wait.h"
#include "unistd.h"
#include "stdio.h"
#include "stdlib.h"
#include "linux/gpio_syscalls.h"
int main(void) {
int rtc;
int sec;
rtc=fork();
if (rtc==0) {
printf("Child: Fork\n");
printf("Child: DL1 on\n");
gpioclearbits(PORTA, PA3);
sleep(7);
printf("Child: DL1 off\n");
gpiosetbits(PORTA, PA3);
return EXIT_SUCCESS;
}
printf("Parent: Fork\n");
for (sec=10;sec>0;sec--) {
printf("Parent: %02d\n",sec);
sleep(1);
}
wait(NULL);
return EXIT_SUCCESS;
}
|
Execute it
# ./fork1
Child: Fork
Child: DL1 on
Parent: Fork
Parent: 10
Parent: 09
Parent: 08
Parent: 07
Parent: 06
Parent: 05
Parent: 04
Child: DL1 off
Parent: 03
Parent: 02
Parent: 01
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