Examples&Exercises:

• Complete the following codes if necessary, then compile and run the code.
• Analyze the code and output.

1. Using a Signal Handler; completed. http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/sigusr1works.csigusr1works.c

   #include <signal.h>
   #include <stdio.h>
   #include <string.h>
   #include <sys/types.h>
   #include <unistd.h>
   #include <time.h>
   sig_atomic_t sigusr1_count = 0;
   void handler (int signal_number)
   {
     time_t cur_time;
     char *chartime;
     int stat;
     cur_time = time(NULL);
     if ( cur_time == -1 ) {
       perror( "Error getting time");
       exit(1);
     }
     chartime = ctime(&cur_time);
     printf( "SIGUSR1 received on %s", ctime(&cur_time) );
     ++sigusr1_count;
     printf ("IN HANDLER: SIGUSR1 was raised %d times\n", sigusr1_count);
   }
   int main ()
   {
     int i,j;
     pid_t child[5];
     struct sigaction sa;
     memset (&sa, 0, sizeof (sa));
     sa.sa_handler = &handler;
     sigaction (SIGUSR1, &sa, NULL);
     child[1]=fork();
     if (child[1] !=0)
       printf("I am the parent  \n");
     else
       {
         sleep(5);
         int pid = getpid();
         printf("\n I am the first child with pid=%d   \n",pid);
         kill(pid,SIGUSR1);
         child[2]=fork();
         if (child[2] !=0)
           printf("I am the parent of the second child \n");
         else
           {
             sleep(5);
             int pid = getpid();
             printf("\n I am the second child with pid=%d   \n",pid);
             kill(getpid(),SIGUSR1);
           }
       }
     printf ("IN MAIN: SIGUSR1 was raised %d times\n", sigusr1_count);
     printf ("******************************************");
     return 0;
   }
   

   • Analyze the code and output.
   • What is the function of tje system call kill? Does It actually kill the process? If not, what is the functionality of that?
2. Cleaning Up Children Asynchronously; completed. http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/cleaningworks.ccleaningworks.c

   #include <signal.h>
   #include <string.h>
   #include <sys/types.h>
   #include <sys/wait.h>
   sig_atomic_t child_exit_status;
   void clean_up_child_process (int signal_number)
   {
     /* Clean up the child process.  */
     int status;
     printf("I am in clenup function now and cleaning this child \n");
     wait (&status);
     /* Store its exit status in a global variable.  */
     child_exit_status = status;
     printf("child_exit_status=%d with pid=%d \n", child_exit_status,
             getpid());
     printf("bla bla bla \n");
     printf("-------------------------------------------------------\n");
   }
   int main ()
   {
     pid_t child_pid,child2;
     /* Handle SIGCHLD by calling clean_up_child_process.  */
     struct sigaction sigchld_action;
     memset (&sigchld_action, 0, sizeof (sigchld_action));
     sigchld_action.sa_handler = &clean_up_child_process;
     sigaction (SIGCHLD, &sigchld_action, NULL);
     printf("Before child_exit_status=%d with pid=%d \n",
             child_exit_status, getpid());
     printf("-------------------------------------------------------\n");
     child_pid=fork();
     if (child_pid!=0)
       {
         sleep(5);
         printf("I am the parent  \n");
       }
     else
       {
         child2=fork();
         if(child2!=0)
           {
             sleep(4);
             printf("I am the first child with pid=%d and
             child_exit_status= %d  \n",getpid(),child_exit_status);
           }
         else
           {
             sleep(3);
             printf("I am the second child with pid=%d and 
             child_exit_status=%d  \n",getpid(),child_exit_status);
           }
       }
     return 0;
   }
   

   • Comment the lines contains sleep out and observe the changes.
     
3. Catching signals; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/sig_talk.csig_talk.c.
   • Study the code to understand the signal catching mechanism.
4. Thread Creation; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/thread-create.cthread-create.c

   #include <pthread.h>
   #include <stdio.h>
   /* Prints x's to stderr.  The parameter is unused.  Does not return.  */
   void* print_xs (void* unused)
   {
     while (1) 
       fputc ('x', stderr);
     return NULL;
   }
   /* The main program.  */
   int main ()
   {
     pthread_t thread_id;
     /* Create a new thread.  The new thread will run the print_xs
        function.  */
     pthread_create (&thread_id, NULL, &print_xs, NULL);
     /* Print o's continuously to stderr.  */
     while (1) 
       fputc ('o', stderr);
     return 0;
   }
   

   • You should break the execution by $<ctrl+c>$.
   • Add a mechanism to catch or to handle the signal to the code.
5. Passing Data to Threads; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/thread-create2.cthread-create2.c
   • Study the code.
   • Add the pthread_join functions.
   • Execute several times to observe the changes in the output pattern.
6. Thread Return Values; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/primes.cprimes.c.
   • Study the code.
   • Modify the code to print out all the prime numbers up to $n^{th}$ one.
7. Thread Attributes; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/detached.cdetached.c.
   • Study the code.
   • Modify http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/thread-create2.cthread-create2.c to add detachstate attribute so that joining the threads will not be needed.
8. Thread-Specific Data; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/tsd.ctsd.c
   • Study the code.