How to handle SIGCHLD in multiprocessing.

Author: Anton Yarkov

multithreading/01 - Signals_SIGCHLD.c

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+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+#define EXIT_FAILURE 1
+
+// To compile:
+// gcc -std=gnu99 "01 - Signals_SIGCHLD.c" -o signals_sigchld
+
+// Task:
+// Create a program which creates a child process and handles SIGCHLD signal from its childs.
+
+void kill_child_handler(int sig)
+{
+    int status;
+    pid_t done = waitpid(
+        -1, // Any child
+        &status,
+        0); // Blocked mode.
+    if (done == -1)
+    {
+        printf("No more child processes.\n", done);
+    }
+    else
+    {
+        short isNormalTermination = WIFEXITED(status);
+        if (!isNormalTermination ||
+            // WEXITSTATUS should be used only if normal termination = true.
+            (isNormalTermination && WEXITSTATUS(status) != 0))
+        {
+            printf("Zombie for PID -- %d failed.\n", done);
+            exit(EXIT_FAILURE);
+        }
+        else
+        {
+            printf("Zombie for PID -- %d successfully removed.\n", done);
+        }
+    }
+}
+
+void main()
+{    
+    pid_t main_pid = getpid();
+    
+    printf("Start of process %d\n", main_pid);
+    
+    // Handle child process killing.
+    struct sigaction kill_child_signal;
+    kill_child_signal.sa_handler = kill_child_handler;
+    sigemptyset(&kill_child_signal.sa_mask);
+    kill_child_signal.sa_flags = SA_RESTART; // Permanent handler.
+    
+    if (sigaction(SIGCHLD, &kill_child_signal, 0) == -1)
+    {
+        perror("Error of calling sigaction");
+        exit(EXIT_FAILURE);
+    }
+
+    // Make child.
+    pid_t child_pid;
+    if(child_pid = fork())
+    {
+        printf("Started child process %d.\n", child_pid);
+        
+        printf("Parent process works 1 second.\n");
+        
+        sleep(1);
+    }
+    else
+    {
+        // Do anything in child.
+    }
+    
+    printf("End of process %d\n", getpid());
+        
+    exit(0);
+}