signal handler for SIGCHLD Post: 76611

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Top Forums Programming signal handler for SIGCHLD Post 76611 by jens on Wednesday 29th of June 2005 11:03:51 AM

06-29-2005

Registered User

signal handler for SIGCHLD

Hi,

I have an c++ application which uses the function fork and execvp().
The parent does not wait until the child ends. The parents just creates children and let them do their stuff.
You can see the parent program as a batch-manager.

I have added a SIGCHLD handler to the program:

void zombie_handler(int iSignal)
{
signal(SIGCHLD,zombie_handler); //reset handler to catch SIGCHLD for next time;
int status;
pid_t pid;

pid = wait(&status); //After wait, child is definitely freed.
printf("pid = %d , status = %d\n", pid, status);
}

int main(int argc,char* argv[])
{
signal(SIGCHLD,zombie_handler);
...
while (condition)
{
fork();
//do child-actions & do not wait for child to finish. We can't afford to wait...
}
}

- How can i avoid signal races in this case? I don't want another SIGCHLD-signal while I'm busy with processing a SIGCHLD-signal !! I don't want to ignore the signal neither when I'm processing a SIGCHLD-signal (cant afford to loose information about childs)
- In the signal-handler I have added the wait() function. The time that wait will need will be none, because the child has already been terminated but is not freed yet? Am I correct?

Can anyone help me with this?

Best regards,
Jens

jens

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LEARN ABOUT OPENDARWIN

pthread_atfork

PTHREAD_ATFORK(3)					     Library Functions Manual						 PTHREAD_ATFORK(3)

NAME

       pthread_atfork - register handlers to be called at fork(2) time

SYNOPSIS

       #include <pthread.h>

       int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void));

DESCRIPTION

       pthread_atfork  registers handler functions to be called just before and just after a new process is created with fork(2). The prepare han-
       dler will be called from the parent process, just before the new process is created. The parent handler will  be  called  from  the  parent
       process, just before fork(2) returns. The child handler will be called from the child process, just before fork(2) returns.

       One or several of the three handlers prepare, parent and child can be given as NULL, meaning that no handler needs to be called at the cor-
       responding point.

       pthread_atfork can be called several times to install several sets of handlers. At fork(2) time, the prepare handlers are  called  in  LIFO
       order  (last  added  with  pthread_atfork,  first  called before fork), while the parent and child handlers are called in FIFO order (first
       added, first called).

       To understand the purpose of pthread_atfork, recall that fork(2) duplicates the whole memory space,  including  mutexes	in  their  current
       locking	state, but only the calling thread: other threads are not running in the child process.  The mutexes are not usable after the fork
       and must be initialized with pthread_mutex_init in the child process.  This is a limitation of the  current  implementation  and  might	or
       might not be present in future versions.

RETURN VALUE

       pthread_atfork returns 0 on success and a non-zero error code on error.

ERRORS

       ENOMEM insufficient memory available to register the handlers.

AUTHOR

       Xavier Leroy <Xavier.Leroy@inria.fr>

SEE ALSO

       fork(2), pthread_mutex_lock(3), pthread_mutex_unlock(3).

								   LinuxThreads 						 PTHREAD_ATFORK(3)

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