Signal Handling in C

Description

This project contains a series of C programs that demonstrate various aspects of signal handling in Unix-like operating systems. These programs illustrate how to handle signals using signal handlers, how to send signals between processes, and how to use alarms and the setjmp/longjmp functions for non-local jumps. Each file showcases different aspects of signal handling, providing a comprehensive overview of how to implement these mechanisms in C.

Key Features

• Signal Handlers: Examples of setting up signal handlers using the signal function.
• Inter-Process Signals: Demonstrations of sending signals between processes using the kill function.
• Alarms: Usage of the alarm function to send SIGALRM signals after a specified amount of time.
• Non-Local Jumps: Examples of using setjmp and longjmp for non-local jumps in response to signals.

Files

1. A1P8.c

   • Demonstrates setting up signal handlers for all signals and handling them.
   • Key Code Snippet:

     #include <signal.h>
     #include <unistd.h>
     #include <stdio.h>
     
     void atrapa(int);
     
     int main() {
         int i;
         for(i = 1; i <= 64; i++)
             signal(i, atrapa);
         printf("Identificativo de proceso: %d\n", getpid());
         pause();
         printf("Continuando...\n");
     }
     
     void atrapa(int sig) {
         signal(sig, atrapa);
         printf("Recibida la señal: %d\n", sig);
     }

     This code sets up a signal handler for all signals and pauses the process until a signal is received.

2. A2P8.c

   • Illustrates the use of the alarm function to send SIGALRM signals at specified intervals.
   • Key Code Snippet:

     #include <signal.h>
     #include <unistd.h>
     #include <stdio.h>
     
     void atrapa(int);
     
     int main() {
         int i;
         signal(SIGALRM, atrapa);
         printf("Identificativo de proceso: %d\n", getpid());
         alarm(5);
         pause();
         alarm(3);
         pause();
         for(i = 1; i < 10; i++) {
             alarm(1);
             pause();
         }
         return 0;
     }
     
     void atrapa(int sig) {
         signal(sig, atrapa);
         printf("RIIIIIIING!\n");
     }

     This code sets up a signal handler for SIGALRM and uses alarm to send SIGALRM signals at intervals.

3. A3P8.c

   • Demonstrates sending SIGUSR1 and SIGKILL signals from a child process to a parent process.
   • Key Code Snippet:

     #include <sys/types.h>
     #include <stdio.h>
     #include <unistd.h>
     #include <signal.h>
     #include <stdlib.h>
     
     void atrapa(int sig) {
         signal(sig, atrapa);
         printf("SIGUSR1, magnicidio\n");
     }
     
     int main() {
         pid_t padre, hijo;
         padre = getpid();
         signal(SIGUSR1, atrapa);
         if((hijo = fork()) == 0) {
             sleep(1);
             kill(padre, SIGUSR1);
             sleep(1);
             kill(padre, SIGUSR1);
             sleep(1);
             kill(padre, SIGUSR1);
             sleep(1);
             kill(padre, SIGKILL);
             exit(0);
         } else { /* padre */
             for (;;);
         }
     }

     This code sets up a signal handler for SIGUSR1 and sends SIGUSR1 and SIGKILL signals from the child process to the parent process.

4. A4P8.c

   • Illustrates sending a termination signal (SIGTERM) from a parent process to a child process.
   • Key Code Snippet:

     #include <stdio.h>
     #include <signal.h>
     #include <stdlib.h>
     
     int main() {
         int pid, i = 10;
         if((pid = fork()) == 0) {
             while(i != 0) {
                 printf("HIJO, PID = %d\n", getpid());
                 i--;
                 sleep(1);
             }
         } else {
             sleep(10);
             printf("PADRE. Terminacion del proceso %d\n", getpid());
             kill(pid, SIGTERM);
         }
         exit(0);
     }

     This code creates a child process that prints its PID every second for 10 seconds, after which the parent process sends a termination signal (SIGTERM) to the child process.

5. A5P8.c

   • Demonstrates the use of setjmp and longjmp for non-local jumps in response to a signal.
   • Key Code Snippet:

     #include <signal.h>
     #include <stdio.h>
     #include <stdlib.h>
     #include <setjmp.h>
     
     jmp_buf entorno;
     void atrapa(int);
     
     int main() {
         int valor;
         printf("longjmp y setjmp son una forma de simular el 'goto'\n\n");
         signal(SIGUSR1, atrapa);
         valor = setjmp(entorno);
         if(valor == 0) {
             printf("Inicia el punto de interrupcion del proceso.\n");
             sleep(1);
         }
         printf("Regreso al punto de interrupcion del proceso.\n");
     }
     
     void atrapa(int sig) {
         signal(SIGUSR1, atrapa);
         longjmp(entorno, sig);
     }

     This code sets up a signal handler for SIGUSR1 and uses setjmp and longjmp to perform a non-local jump when the signal is received.

How to Use

1. Compilation: Each C file can be compiled using a C compiler such as gcc.

   gcc A1P8.c -o A1P8
   gcc A2P8.c -o A2P8
   gcc A3P8.c -o A3P8
   gcc A4P8.c -o A4P8
   gcc A5P8.c -o A5P8

2. Execution: Run the compiled programs to see the output of signal handling operations.

   ./A1P8
   ./A2P8
   ./A3P8
   ./A4P8
   ./A5P8