API for handling wait queues are not working - process

Question

I have to make tasks as processes in Linux but I don't want the process to execute until all the processes are created. So I thought of moving the processes to wait queue soon after creation and wait until all processes are created.
#include <unistd.h> /* Symbolic Constants */
#include <sys/types.h> /* Primitive System Data Types */
#include <errno.h> /* Errors */
#include <stdio.h> /* Input/Output */
#include <stdlib.h> /* General Utilities */
#include <pthread.h> /* POSIX Threads */
#include <string.h> /* String handling */
#include <sched.h>
#include <linux/kernel.h>
#include <time.h>
#include <sys/resource.h>
#include <stddef.h>
#include <linux/sched.h>
#include <linux/wait.h> /* for wait_event_interruptible() & wake_up_interruptible() */
int done = 0;
static DECLARE_WAIT_QUEUE_HEAD(queue);
int main()
{
int pid1, pid2;
if ((pid1 = fork()) < 0) //create a child process
exit(1);
if ((pid2 = fork()) < 0) //create a child process
exit(1);
if (pid1 == 0) //child process
{
wait_event_interruptible(queue, done == 2);
printf("child 1\n");
}
else //parent process
{
done = done+1;
wake_up_interruptible(&queue);
}
if (pid2 == 0) //child process
{
wait_event_interruptible(queue, done == 2);
printf("child 2\n");
}
else //parent process
{
done = done+1;
wake_up_interruptible(&queue);
}
return 0;
}
But when I tried this sample code it shows these errors.
$ gcc -Wall try.c
try.c:18:8: warning: type defaults to ‘int’ in declaration of ‘DECLARE_WAIT_QUEUE_HEAD’ [-Wimplicit-int]
try.c:18:1: warning: parameter names (without types) in function declaration [enabled by default]
try.c: In function ‘main’:
try.c:33:6: warning: implicit declaration of function ‘wait_event_interruptible’ [-Wimplicit-function-declaration]
try.c:33:31: error: ‘queue’ undeclared (first use in this function)
try.c:33:31: note: each undeclared identifier is reported only once for each function it appears in
try.c:39:2: warning: implicit declaration of function ‘wake_up_interruptible’ [-Wimplicit-function-declaration]
try.c: At top level:
try.c:18:8: warning: ‘DECLARE_WAIT_QUEUE_HEAD’ declared ‘static’ but never defined [-Wunused-function]
When I checked $ man wait_event_interruptible, it says "No manual entry for wait_event_interruptible". So the API is missing in the library. How can I add it to the library? Thanks in advance.

Answer 1

wait_event_interruptible(), wake_up_interruptible() are some of the Kernel's API to create and use wait queues. You cannot use those from the user-land!
If I understand your purpose correctly, what you need to do is to create N processes barrier. If you know the number of the processes (N), you can easily use semaphores: initialize the semaphore with zero, all processes call down() and the last process calls up() N times. You can also use message queues.
You can also use the Linux API for barriers: pthread_barrier_wait and pthread_barrier_init, but I have not used this before.