Example of waitpid() in use?

I know that waitpid() is used to wait for a process to finish, but how would one use it exactly?

Here what I want to do is, create two children and wait for the first child to finish, then kill the second child before exiting.

//Create two children
pid_t child1;
pid_t child2;
child1 = fork();

//wait for child1 to finish, then kill child2
waitpid() ... child1 {
kill(child2) }

waitpid() - Unix, Linux System Call, EXAMPLE. The following program demonstrates the use of fork(2) and waitpid(2). The program creates a child process. If no command-� If pidis equal to zero, waitpid() waitsfor termination of any child whose process group ID is equal to thatof the caller. If pidis -1, waitpid() waits for anychild process to end. If pidis less than -1, waitpid() waitsfor the termination of any child whose process group ID is equal tothe absolute value of pid.

The syntax is

pid_t waitpid(pid_t pid, int *statusPtr, int options);

1.where pid is the process of the child it should wait.

2.statusPtr is a pointer to the location where status information for the terminating process is to be stored.

3.specifies optional actions for the waitpid function. Either of the following option flags may be specified, or they can be combined with a bitwise inclusive OR operator:

WNOHANG WUNTRACED WCONTINUED

If successful, waitpid returns the process ID of the terminated process whose status was reported. If unsuccessful, a -1 is returned.

benifits over wait

1.Waitpid can used when you have more than one child for the process and you want to wait for particular child to get its execution done before parent resumes

2.waitpid supports job control

3.it supports non blocking of the parent process

waitpid -- Wait for a Specific Process to End, #include <sys/types.h> #include <sys/wait.h> pid_t waitpid(pid_t pid, The following example illustrates the use of waitpid to wait for a process to end: # include� The following are 30 code examples for showing how to use os.waitpid().These examples are extracted from open source projects. You can vote up the ones you like or vote down the ones you don't like, and go to the original project or source file by following the links above each example.

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>

int main (){
    int pid;
    int status;

    printf("Parent: %d\n", getpid());

    pid = fork();
    if (pid == 0){
        printf("Child %d\n", getpid());
        sleep(2);
        exit(EXIT_SUCCESS);
    }

//Comment from here to...
    //Parent waits process pid (child)
    waitpid(pid, &status, 0);
    //Option is 0 since I check it later

    if (WIFSIGNALED(status)){
        printf("Error\n");
    }
    else if (WEXITSTATUS(status)){
        printf("Exited Normally\n");
    }
//To Here and see the difference
    printf("Parent: %d\n", getpid());

    return 0;
}

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� EXAMPLE. The following example illustrates the use of waitpidto wait for a process to end: #include <sys/types.h> #include <sys/wait.h> #include <unistd.h> #include <time.h> #include <stdio.h> #include <stdlib.h> int main(void) { int i, status; pid_t childID, endID; time_t when; if ((childID = fork()) == -1) { /* Start a child process.

waitpid() — Wait for a specific child process to end, More precisely, waitpid() suspends the calling process until the system gets status information on the child. If pid is greater than 0, waitpid() waits for termination of the specific child Example. CELEBW02 ⁄* CELEBW02 The following function suspends the Contact � Privacy � Terms of use � Accessibility; Feedback. waitpid PID,FLAGS Waits for a particular child process to terminate and returns the pid of the deceased process, or -1 if there is no such child process. A non-blocking wait (with WNOHANG in FLAGS) can return 0 if there are child processes matching PID but none have terminated yet.

waitpid(2): wait for process to change state, If status is not NULL, wait() and waitpid() store status information in the int to Example. The following program demonstrates the use of fork(2) and waitpid(). EXAMPLES top Waiting for a Child Process and then Checking its Status The following example demonstrates the use of waitpid(), fork(), and the macros used to interpret the status value returned by waitpid() (and wait()). The code segment creates a child process which does some unspecified work.

[PDF] waitpid(pid, &status, WNOHANG|WUNTRACED), WUNTRACED: report status of terminated or stopped children. In Lab 4, use: waitpid(-1, &status, WNOHANG|WUNTRACED). In sigchld_handler(): while (( c_pid� We know if more than one child processes are terminated, then wait() reaps any arbitrarily child process but if we want to reap any specific child process, we use waitpid() function. Syntax in c language: pid_t waitpid (child_pid, &status, options); Options Parameter

Comments
  • I note that the wait(2) man page on my Linux system includes an actual example of how to use the waitpid() system call.
  • I think you could find the answer rather easily by searching on SO for [c] waitpid; rather less easily by searching for [c] [waitpid]. I've answered 48 questions with the first search and 5 with the second, and I'm by no means the only person who has answered such questions.
  • support.sas.com/documentation/onlinedoc/sasc/doc/lr2/… provides much more detailed information with an example. I personally still could not understand how to use waitpid effectively from the 2 answers to this question here.
  • Have you read the documentation about 1) return value of waitpid, 2) when it is appropriate to use WEXITSTATE, 3) what would the most normal of normal exits return for WEXITSTATUS...
  • You might explain your answer a bit?