/*********************************************************************************
 *      Copyright:  (C) 2025 LingYun IoT System Studio
 *                  All rights reserved.
 *
 *       Filename:  signal.c
 *    Description:  This file is signal example program
 *
 *        Version:  1.0.0(11/07/2025)
 *         Author:  Guo Wenxue <guowenxue@gmail.com>
 *      ChangeLog:  1, Release initial version on "11/07/2025 10:18:12 AM"
 *
 ********************************************************************************/
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>

int g_child_stop = 0;
int g_parent_run = 0;

void sig_child(int signum)
{
	if( SIGUSR1 == signum )
	{
		g_child_stop = 1;
	}
}

void sig_parent(int signum)
{
	if( SIGUSR2 == signum )
	{
		g_parent_run = 1;
	}
}

int main(int argc, char **argv)
{
	int             pid;
	int             wstatus;

	signal(SIGUSR1, sig_child);
	signal(SIGUSR2, sig_parent);

	if( (pid=fork()) < 0 )
	{
		printf("Create child process failure: %s\n", strerror(errno));
		return -2;
	}
	else if(pid == 0)
	{
		/* child process can do something first here */
		printf("Child process working...\n");
		sleep(1);

		printf("Child process done and send parent signal SIGUSR2\n");
		kill(getppid(), SIGUSR2);

		while( !g_child_stop )
		{
			sleep(1);
		}

		printf("Child process receive signal from parent and exit now\n");
		return 0;
	}

	printf("Parent hangs up to wait for signal from child\n");
	while( !g_parent_run )
	{
		sleep(1);
	}

	/* parent process can do something here */
	printf("Parent process working...\n");
	sleep(1);

	printf("Parent process done and send child signal SIGUSR1\n");
	kill(pid, SIGUSR1);

	/* parent wait child process exit */
	wait(&wstatus);
	printf("Parent process receive signal from child and exit now\n");

	return 0;
}