Creating a auto terminating main function - c

Question

The following program implements two array of threads.There are two thread functions student and teacher(I have not shown them here). My sample program is given below. I want to make a time limit(say 10 sec) after which the main thread will automatically exit no matter if others threads have completed or not.I also want to the current time every moment after starting of the program. How will I do that?
Sample code fragment:
int main(void)
{
pthread_t thread1[25];
pthread_t thread2[6];
int i;
int id1[25]; //for students
int id2[6]; //for teachers
for(i=0;i<25;i++)
{
id1[i]=i;
id2[i]=i;
pthread_create(&thread1[i],NULL,student,(void*)&id1[i] );
if(i<6)
{
pthread_create(&thread2[i],NULL,teacher,(void*)&id2[i]);
}
}
for (i=0;i<25;i++)
{
pthread_join(thread1[i],NULL);
if(i<6)
{
pthread_join(thread2[i],NULL);
}
}
return 0;
}
What additional things will I have to add to the above code to terminate the main thread after a certain time? (say: 10 seconds)

Answer 1

You can use pthread_timedjoin_np() for this passing a timespec struct. You can set the struct to timeout after 10 seconds like this:
struct timespec tp;
tp.tv_sec = 10;
tp.tv_nsec = 0;
Then you change your calls to join pthread_timedjoin_np(myThread, &tp). Regarding how you can get the current time, the simplest method is to use gettimeofday function.
Another perhaps simpler approach is to use a alarm. You can have a function which will exit the application. So you would do something like this:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>
void alarmhandler(int sig) {
printf("Ten seconds passed, quitting!\n");
exit(0);
}
int main() {
int i, j;
struct timeval end, start;
signal(SIGALRM, alarmhandler);
alarm(4);
gettimeofday(&start, NULL);
sleep(3); // simulate thread work
gettimeofday(&end, NULL);
long elapsed = (end.tv_sec-start.tv_sec)*1000000 + end.tv_usec-start.tv_usec;
printf("%f seconds elapsed!\n", (float)(elapsed)/1000000.0f);
for(;;); // block indefinitely
}