Understanding the Wait System Call in C Programming

The wait system call in C programming is used to block the calling process until one of its child processes exits or a signal is received. This practical guide provides detailed explanations and C program examples to demonstrate the working of the wait system call, including handling child processes, parent-child communication, and process termination. Explore the concepts and practical implementation of the wait system call in C programming.

• C Programming
• Wait System Call
• Child Processes
• Process Termination
• Parent-Child Communication

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1. Wait System Call Practical No 3

2. Wait System Call in C A call to wait() blocks the calling process until one of its child processes exits or a signal is received. After child process terminates, parent continues its execution after wait system call instruction. Child process may terminate due to any of these: It calls exit(); It returns (an int) from main It receives a signal (from the OS or another process) whose default action is to terminate.

4. C program to demonstrate working of wait() #include<stdio.h> #include<stdlib.h> #include<sys/wait.h> #include<unistd.h> int main() { pid_t cpid; if (fork()== 0) exit(0); /* terminate child */ else cpid = wait(NULL); /* reaping parent */ printf("Parent pid = %d\n", getpid()); printf("Child pid = %d\n", cpid); return 0; }

5. Another C program to demonstrate working of wait() #include<stdio.h> #include<sys/wait.h> #include<unistd.h> int main() { if (fork()== 0) printf("HC: hello from child\n"); else { printf("HP: hello from parent\n"); wait(NULL); printf("CT: child has terminated\n"); } printf("Bye\n"); return 0; }

6. waitpid-example.c if (pid == 0) { int i; for (i = 3; i > 0; i--) { printf("This is the child\n"); sleep(1); } exit(3); } else { int stat_val; waitpid(pid, &stat_val, 0); //waitpid(pid, &stat_val); printf("exit code: %d, signal: %d, raw stat_val: 0x%x %d"); } return 0; } #include <sys/types.h> #include <sys/wait.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> int main(void) { pid_t pid; pid = fork(); if (pid < 0) { perror("fork failed"); exit(1); }

7. printf("Child: %d: I'm the child\n", pid, c_pid); printf("Child: sleeping for 2-seconds, then exiting with status 12\n"); *get_exitstatus.c*/ #include <unistd.h> #include <stdio.h> #include <stdlib.h> //sleep for 2 seconds sleep(2); //exit with statys 12 exit(12); }else if (c_pid > 0){ //parent //waiting for child to terminate pid = wait(&status); #include <sys/types.h> #include <sys/wait.h> int main(){ if ( WIFEXITED(status) ){ printf("Parent: Child exited with status: %d\n", WEXITSTATUS(status)); } pid_t c_pid, pid; int status; }else{ //error: The return of fork() is negative perror("fork failed"); _exit(2); //exit failure, hard } c_pid = fork(); //duplicate if( c_pid == 0 ){ //child pid = getpid(); return 0; //success }