The Wait System Call in C Programming
Wait System Call
Practical No 3
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.
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;
}
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;
}
waitpid-example.c
#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);
}
exit(3);
} else {int stat_val;
waitpid(pid, &stat_val, 0);
//waitpid(pid, &stat_val, WNOWAIT);
if (WIFEXITED(stat_val))
printf("Child exited with code %d\n", WEXITSTATUS(stat_val));else if (WIFSIGNALED(stat_val))
printf("Child terminated abnormally, signal %d\n", WTERMSIG(stat_val)); printf("exit code: %d, signal: %d, raw stat_val: 0x%x %d", WEXITSTATUS(stat_val), WTERMSIG(stat_val), stat_val, stat_val);}
return 0;
}
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;
}
•
*get_exitstatus.c*/
•
#include <unistd.h>
•
#include <stdio.h>
•
#include <stdlib.h>
•
#include <sys/types.h>
•
#include <sys/wait.h>
•
int main(){•
pid_t c_pid, pid;
•
int status;
•
c_pid = fork(); //duplicate
•
if( c_pid == 0 ){•
//child
•
pid = getpid();
printf("Child: %d: I'm the child\n", pid, c_pid); printf("Child: sleeping for 2-seconds, then exiting with status 12\n");//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);
if ( WIFEXITED(status) ){ printf("Parent: Child exited with status: %d\n", WEXITSTATUS(status));}
}else{//error: The return of fork() is negative
perror("fork failed");_exit(2); //exit failure, hard
}
return 0; //success
}
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.
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Presentation Transcript
Wait System Call Practical No 3
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.
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; }
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; }
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); }
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 }
