Description

Total 1 point
Objective
At the end of this mini-lab, you will be able to:
• Gain hands-on experience in using signals as an inter-process communication method.
Instructions
Signals serve as a limited form of inter-process communication (IPC), acting as software interrupts. In this task, you will customize the SIGUSR1 signal to terminate the process. To achieve this, we can utilize the signal function, and its signature is as follows.
signal(int sig , void (*handler)(int));
1. Open two terminals in VS Code under the same directory with lab2-signal.c.
2. In Terminal 1, compile and run lab2-signal.c without any modification. The program will run a dead-loop and write to local file ./pid.txt its process id for us to terminate it.
3. In Terminal 2, execute kill -10 $(cat ./pid.txt) to send an SIGUSR1 signal (sigusr1(10)) using the command kill to the process id stored in ./pid.txt or press Ctrl + c in Terminal 1.
Before redefining SIGUSR1 handler: the program in Ternimal 1 will be terminated and print out “<pid> user-defined signal 1 <file>”, which is the default behavior of SIGUSR1.
4. Complete TODO1&TODO2 in lab2-signal.c to terminate the process immediately without any message once SIGUSR1 is received. Compile, and run it again in Terminal 1.
5. In Terminal 2, execute kill -10 $(cat ./pid.txt) again.
After redefining SIGUSR1 handler : The default handler will be replaced to terminating process immediately and the dead loop will exit.
1
6. In Terminal 2, terminate the dead loop using kill -10 $(cat ./pid.txt).
Customize signal handler: Some useful handler behaviors are: 1)ignoring some control signals like SIGINT, 2) ignoring exception, like SIGFPE (float-point error) and continuing.
Note: Not all signals are redefinable, e.g., sigkill(9).
Submission
(1 pt) Complete all TODO sections and submit your code as lab2-signal_<your_student_id>.c.
COMP3230 Mini-lab 2 Page 2
Appendix
// filename: lab2-signal.c
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void sigusrHandler(int sig_num)
{
// TODO2: Terminate the program when the SIGUSR1 signal is caught. (~1 line)
}
int main()
{
// TODO1: Set the signal handler for SIGUSR1 to the function sigusrHandler using the signal function. (~1 line)
// Write pid to a local file named pid.txt FILE *fp;
fp = fopen(“pid.txt”, “w”); fprintf(fp, “%d”, getpid()); fclose(fp);
/* An infinite loop. */ while(1) { printf(“Still running… “); sleep(1);
}
return 0;
}
COMP3230 Mini-lab 2 Page 3