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signal handler for SIGCHLD

 
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Old 06-29-2005
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
 
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LEARN ABOUT V7

wait

WAIT(2) 							System Calls Manual							   WAIT(2)

NAME

       wait - wait for process to terminate

SYNOPSIS

       wait(status)
       int *status;

       wait(0)

DESCRIPTION

       Wait  causes its caller to delay until a signal is received or one of its child processes terminates.  If any child has died since the last
       wait, return is immediate; if there are no children, return is immediate with the error bit set (resp. with a value of -1  returned).   The
       normal return yields the process ID of the terminated child.  In the case of several children several wait calls are needed to learn of all
       the deaths.

       If (int)status is nonzero, the high byte of the word pointed to receives the low byte of the argument of exit when  the	child  terminated.
       The  low  byte  receives the termination status of the process.	See signal(2) for a list of termination statuses (signals); 0 status indi-
       cates normal termination.  A special status (0177) is returned for a stopped process which has not terminated and can  be  restarted.   See
       ptrace(2).  If the 0200 bit of the termination status is set, a core image of the process was produced by the system.

       If the parent process terminates without waiting on its children, the initialization process (process ID = 1) inherits the children.

SEE ALSO

       exit(2), fork(2), signal(2)

DIAGNOSTICS

       Returns -1 if there are no children not previously waited for.

ASSEMBLER

       (wait = 7.)
       sys wait
       (process ID in r0)
       (status in r1)

       The high byte of the status is the low byte of r0 in the child at termination.

																	   WAIT(2)