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Full Discussion: process
Top Forums Programming process Post 61501 by thumsup9 on Friday 4th of February 2005 10:49:07 AM
Old 02-04-2005
From google
fork() causes a process to duplicate. The child process is an almost-exact
duplicate of the original parent process; it inherits a copy of its parent's
code, data, stack, open file descriptors, and signal table. However, the parent
and child have different process id numbers and parent process id numbers.

If fork() succeeds, it returns the PID of the child to the parent process,
and returns 0 to the child process. If it fails, it returns -1 to the parent
process and no child is created.

fork() is a strange system call, because one process(the original) calls it, but
two processes(the original and its child) return from it. Both processes continue
to run the same code concurrently, but have completely separate stack and data
spaces.

A process may obtain its own process id and parent process id numbers by
using the getpik() and getppid() system calls, respectively. Here's a synopsis
of these system calls:

System Call: int getpid()
int getppid()

getpid() and getppid() return a process's id and parent process's id numbers,
respectively. They always succeed. The parent process id number of PID 1 is 1.

To illustrate the operation of fork(), here's a small program that duplicates and
then branches based on the return value of fork():
Code:
$ cat fork.c
#include <stdio.h>
main()
{
    int pid;
    printf("I'm the original process with PID %d and PPID %d.\n",
           getpid(),getppid());
    pid=fork();  /* Duplicate. Child and parent continue from here.*/
    if (pid!=0)  /* pid is non-zero, so I must be the parent  */
        {
           printf("I'm the parent process with PID %d and PPID %d.\n",
                   getpid(),getppid());
           printf("My child's PID is %d.\n", pid);
        }
    else  /* pid is zero, so I must be the child. */
        {
           printf("I'm the child process with PID %d and PPID %d.\n",
                   getpid(),getppid());
        }
    printf("PID %d terminates.\n",pid);  /* Both processes execute this */
}


$fork.exe ... run the program.
I'm the original process with PID 13292 and PPID 13273.
I'm the parent process with PID 13292 and PPID 13273.
My child's PID is 13293.
I'm the child process with PID 13293 and PPID 13292.
PID 13293 terminates. ... child terminates.
PID 13292 terminates. ... parent terminates.
Last edited by thumsup9; 02-04-2005 at 11:59 AM..
 

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LEARN ABOUT SUNOS

getpgrp

getpid(2)							   System Calls 							 getpid(2)

NAME

       getpid, getpgrp, getppid, getpgid - get process, process group, and parent process IDs

SYNOPSIS

       #include <unistd.h>

       pid_t getpid(void);

       pid_t getpgrp(void);

       pid_t getppid(void);

       pid_t getpgid(pid_t pid);

DESCRIPTION

       The getpid() function returns the process ID of the calling process.

       The getpgrp() function returns the process group ID of the calling process.

       The getppid() function returns the parent process ID of the calling process.

       The getpgid() function returns the process group ID of the process whose process ID is equal to pid, or the process group ID of the calling
       process, if pid is equal to 0.

RETURN VALUES

       Upon successful completion, these functions return the process group ID. Otherwise, getpgid() returns (pid_t)-1 and sets errno to  indicate
       the error.

ERRORS

       The getpgid() function will fail if:

       EPERM	       The  process  whose  process   ID is equal to pid is not in the same session as the calling process, and the implementation
		       does not allow access to the process group ID of that process from the calling process.

       ESRCH	       There is no process with a process ID equal to pid.

       The getpgid() function may fail if:

       EINVAL	       The value of the pid argument is invalid.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       intro(2), exec(2), fork(2), getsid(2), setpgid(2), setpgrp(2), setsid(2), signal(3C), attributes(5), standards(5)

SunOS 5.10							    28 Dec 1996 							 getpid(2)
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