AutoCompilerDaemon.c

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
#include <sys/inotify.h>
#include <poll.h>
#include <sys/wait.h>


int compile(){
	int stat = -1;
	int pdd = fork();
	if(pdd == -1) {
		syslog(LOG_ERR, "Cannot create a fork for Compiler Process");
		exit(EXIT_FAILURE);
	}
	if(pdd == 0){
		execl("/bin/g++", "g++", "/home/ashar/Desktop/AutoCompiler/src/sol.cc", "-Wall","-o","/home/ashar/Desktop/AutoCompiler/src/a.out", NULL);
	}
	else {
		syslog(LOG_INFO, "Waiting for compiler process %d to exit", pdd);
		waitpid(pdd, &stat, 0);
		syslog(LOG_INFO, "Compiler exited with exit code %d", stat);
		return 0;
	}
	return -1;
}

void handle_change(int fd){
	char buf[4096] __attribute__((aligned(__alignof__(struct inotify_event))));
	const struct inotify_event *event = NULL;
	ssize_t len;
	char*ptr;
	while(1){
		len = read(fd, buf, sizeof buf);
		if(len == -1 && errno != EAGAIN){
			syslog(LOG_ERR, "Failed to read from inotify fd");
			exit(EXIT_FAILURE);
		}
		if(len <= 0) break;
		for(ptr = buf; ptr < buf + len; ptr += sizeof(struct inotify_event) + event->len){
			event = (const struct inotify_event *)ptr;
			if(event->mask & IN_CLOSE_WRITE){
				compile();
			}
			else {
			if(event->mask == IN_IGNORED){
				syslog(LOG_ERR, "Watcher was forcefully removed." 
						"Did you used vim to save the file without :set backupcopy=yes");
				}
			else syslog(LOG_WARNING, "Not handling event mask 0x%.8x",event->mask);
			}
		}
	}

}


int main() {
        
        pid_t pid, sid;

        pid = fork();
        
	if (pid < 0) {
		syslog(LOG_ERR, "Cannot fork daemon process.");
                exit(EXIT_FAILURE);
        }
        if (pid > 0) {
		syslog(LOG_INFO, "Fork Success. PID %d", getpid());
                exit(EXIT_SUCCESS);
        }

        umask(0);
	int res = setgid(1000); // Run the Daemon on my user group
	if(res == -1){
		perror("setgid failed");
		exit(EXIT_FAILURE);
	}

	syslog(LOG_INFO, "Starting the AutoCompilerDaemon");

        sid = setsid();
        if (sid < 0) {
		syslog(LOG_ERR, "setsid returned an error");
                exit(EXIT_FAILURE);
        }
        
        if ((chdir("/")) < 0) {
        	syslog(LOG_ERR, "chdir to root failed");
                exit(EXIT_FAILURE);
        }
        

        close(STDIN_FILENO);
        //close(STDOUT_FILENO);
        //close(STDERR_FILENO);
	
	syslog(LOG_INFO, "Closed all File Descriptors");
	syslog(LOG_INFO, "Creating Listener for AutoCompilation of /home/ashar/Desktop/AutoCompiler/src/sol.cc"); 
        
	int fd = inotify_init1(IN_NONBLOCK);
	
	if(fd == -1){
		syslog(LOG_ERR, "Failed to create a inotify instance");
		exit(EXIT_FAILURE);
	}

	int wd = inotify_add_watch(fd, "/home/ashar/Desktop/AutoCompiler/src/sol.cc", IN_CLOSE_WRITE);
	
	if(wd == -1){
		syslog(LOG_ERR, "Failed to add the file watcher to inotify instance");
		exit(EXIT_FAILURE);
	}

	syslog(LOG_INFO, "Starting the polling for the change events in the file");
	
	struct pollfd pfd;
	pfd.fd = fd;
	pfd.events = POLLIN;
	
	syslog(LOG_INFO, "Listening for events on file");

	while (1) {
		int poll_num = poll(&pfd, 1, -1); // Blocking call
		if(poll_num == -1){
			if(errno == EINTR) continue; // Interuppts
			syslog(LOG_ERR, "Polling Error: Failed to poll for the file for fd changes");
			exit(EXIT_FAILURE);
		}
		if(poll_num > 0){
			if(pfd.revents & POLLIN) {
				syslog(LOG_INFO, "File Contents have changed. Recompilation begins now");
				handle_change(fd);
			}
			else syslog(LOG_WARNING, "Polling FD is not POLLIN");
		}

           sleep(30);
        }
   syslog(LOG_INFO, "Shutting down AutoCompilerDaemon");
   exit(EXIT_SUCCESS);
}