Added exercise for signal handler

exercises/README.md

@@ -75,6 +75,21 @@ This is an organized list of all exercises completed so far, including a brief d
 
 ---
 
+## 🚦 signal_handler
+
+**Description**: A C program demonstrating robust signal handling for `SIGINT` and `SIGUSR1` using `sigaction` with `SA_SIGINFO`.
+
+- 📄 [README](signal_handler/README.md)
+- 📂 Directory: `signal_handler/`
+- ✅ Features:
+  - Handles `SIGINT` up to three times before exiting
+  - Handles `SIGUSR1` with a simple message
+  - Masks signals during handler execution to avoid reentrancy issues
+  - Includes comments and clear separation of handler logic
+  - Makefile included with standard targets
+
+---
+
 ## 🔧 Tooling & Automation
 
 **Shared tools and scripts used across projects**:

exercises/signal_handler/Makefile

@@ -0,0 +1,12 @@
+CC = gcc
+CFLAGS = -Wall -Wextra -O2
+TARGET = signal_handler
+SRC = main.c
+
+all: $(TARGET)
+
+$(TARGET): $(SRC)
+	$(CC) $(CFLAGS) -o $(TARGET) $(SRC)
+
+clean:
+	rm -f $(TARGET)

exercises/signal_handler/README.md

@@ -0,0 +1,55 @@
+# Signal Handler
+
+## Overview
+
+This project demonstrates how to handle UNIX signals in C using `sigaction`.  
+It specifically intercepts **SIGINT** and **SIGUSR1** and prints messages when these signals are received.
+
+---
+
+## Features
+
+- Intercepts **SIGINT** (usually generated with `Ctrl + C`) and **SIGUSR1**`.
+- Prints a custom message for each signal.
+- Tracks the number of `SIGINT` signals received and terminates after a defined count.
+- Demonstrates proper use of:
+  - `sigaction()` instead of `signal()` for consistent behavior.
+  - `volatile sig_atomic_t` for safe signal state handling.
+
+---
+
+## Build
+
+```bash
+make
+```
+
+---
+
+## Run
+
+```bash
+./signal_handler
+```
+
+---
+
+## Test
+
+- Open another terminal and run:
+
+```bash
+kill -USR1 <PID>
+```
+
+where `<PID>` is the process ID of `signal_handler`.
+
+- Press `Ctrl + C` in the terminal running the program to send `SIGINT`.
+
+---
+
+## Clean
+
+```bash
+make clean
+```

exercises/signal_handler/main.c

@@ -0,0 +1,58 @@
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+volatile sig_atomic_t sigint_caught = 0;
+
+void signal_handler(int signo, siginfo_t *si, void *ucontext)
+{
+	(void)si;
+	(void)ucontext;
+
+	if (signo == SIGINT) {
+		sigint_caught += 1;
+		if (write(STDOUT_FILENO, "Caught SIGINT signal\n", 22) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+		if (sigint_caught >= 3) {
+			if (write(STDOUT_FILENO, "Reach SIGINT limit\n", 20) ==
+			    -1) {
+				_exit(EXIT_FAILURE);
+			}
+			_exit(EXIT_FAILURE);
+		}
+	} else if (signo == SIGUSR1) {
+		if (write(STDOUT_FILENO, "Caught SIGUSR1 signal\n", 23) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+	} else {
+		if (write(STDOUT_FILENO, "Unknown signal\n", 16) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+	}
+}
+
+int main(void)
+{
+	struct sigaction action;
+	sigemptyset(&action.sa_mask);
+	sigaddset(&action.sa_mask, SIGINT);
+	sigaddset(&action.sa_mask, SIGUSR1);
+	action.sa_sigaction = signal_handler;
+	action.sa_flags = SA_SIGINFO;
+
+	if (sigaction(SIGINT, &action, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+	if (sigaction(SIGUSR1, &action, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	printf("Hi, I'm process with PID %d\n", getpid());
+	for (;;)
+		pause();
+	return EXIT_SUCCESS;
+}