fork()ing hell!! Post: 13998

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Top Forums Programming fork()ing hell!! Post 13998 by Perderabo on Saturday 26th of January 2002 11:25:44 AM

01-26-2002

Administrator Emeritus

You guys are making this much harder than it needs to be. Let's start by forking one process and storing its pid:

Code:

#include &lt;stdio.h>
#include &lt;unistd.h>

void main()
{
        int pid, parentpid, childpid;

        parentpid=getpid();
        printf("I am the parent process and my pid is %d\n", getpid());

        if (pid=fork()) {
                childpid=pid;
        } else {
                printf("I am a child process and my pid is %d\n", getpid());
                exit(0);
        }

        printf("I am still the parent process and my pid is %d\n", getpid());
        exit(0);
}

Here the child process just displays its pid then exits. You will probably want to do more with your child processes, but after your children take care of business they must exit so they participate in any further forking. Also in my example the parent process exits fairly quickly. This means that init will inherit the child process and will reap it when it dies. If I wanted to keep the parent around, I would need to insure that it issues wait() calls for each child who dies. If I didn't do this, the children would become zombies. I usually just let the parent die.

Once we have some code that does what we want, if we want to do it n times, we use a loop:

Code:

#include &lt;stdio.h>
#include &lt;unistd.h>

void main()
{
        int n, pid, parentpid, childpids[10];

        parentpid=getpid();
        printf("I am the parent process and my pid is %d\n", getpid());

        for(n=0; n<5; n++) {
                if (pid=fork()) {
                        childpids[n]=pid;
                } else {
                        printf("I am a child process and my pid is %d\n", 
                                        getpid());
                        exit(0);
                }
        }

        printf("I am still the parent process and my pid is %d\n", getpid());
        exit(0);
}

As requested by the OP, the children's pids are recorded in an array. But I still just let the parent die.

Perderabo

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LEARN ABOUT DEBIAN

ns_execargblk

Ns_Exec(3aolserver)					   AOLserver Library Procedures 				       Ns_Exec(3aolserver)

__________________________________________________________________________________________________________________________________________________

NAME

       Ns_ExecArgblk,  Ns_ExecArgv,  Ns_ExecProc,  Ns_ExecProcess,  Ns_Fork,  Ns_GetEnviron, Ns_WaitForProcess, Ns_WaitProcess, ns_fork - External
       process execution

SYNOPSIS

       #include "ns.h"

       int
       Ns_ExecArgblk(char *exec, char *dir, int fdin, int fdout,
		     char *args, Ns_Set *env)

       int
       Ns_ExecArgv(char *exec, char *dir, int fdin, int fdout,
		   char **argv, Ns_Set *env)

       int
       Ns_ExecProc(char *exec, char **argv)

       int
       Ns_ExecProcess(char *exec, char *dir, int fdin, int fdout,
		      char *args, Ns_Set *env)

       int
       Ns_Fork(void)

       char
       **Ns_GetEnviron(void)

       int
       Ns_WaitForProcess(int pid, int *statusPtr)

       int
       Ns_WaitProcess(int pid)

       int
       ns_fork(void)
_________________________________________________________________

DESCRIPTION

       These functions handle fork and exec operations. See files: nsd/exec.c, nsd/tclenv.c and nsthread/fork.c.

       Ns_ExecArgblk(exec, dir, fdin, fdout, args, env)

	      Executes a command in a child process. Return process id of child process exec'ing the command or -1 on failure.	Provides  extended
	      error checking and error messages.

       Ns_ExecArgv(exec, dir, fdin, fdout, argv, env)

	      Execute a command in a child process using fork(2) and execve(2), returns the process id of child process exec'ing the command or -1
	      on failure. The child sends an extended error message to the parent.

       Ns_ExecProc(exec, argv)

	      Executes a command in a child process. Returns the process id of the child process exec'ing the command or -1 on	failure.   Simpli-
	      fies call to Ns_ExecArgv.

       Ns_ExecProcess(exec, dir, fdin, fdout, args, env)

	      Executes	a  command  in	a child process. Returns the process id of the child process exec'ing the command or -1 on failure.  Calls
	      Ns_ExecArgblk with same arguments.

       Ns_Fork()
	      Posix style fork(), using fork1() on Solaris if needed. See fork(2) man page. Calls ns_fork.

       Ns_GetEnviron()

	      Returns pointer to the environment vector.

       Ns_WaitForProcess(pid, statusPtr)

	      Wait for child process. Returns NS_OK on success, or NS_ERROR on failure. *statusPtr is set to the exit code of the child process.

       Ns_WaitProcess(pid)

	      Wait for child process. Calls Ns_WaitForProcess with NULL statusPtr. Returns NS_OK on success, or NS_ERROR on failure.

       ns_fork()

	      Posix style fork(), using fork1() on Solaris if needed.

SEE ALSO

       nsd(1), info(n)

KEYWORDS

AOLserver								4.0						       Ns_Exec(3aolserver)