Track Child process exit Post: 302440182

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Top Forums Shell Programming and Scripting Track Child process exit Post 302440182 by ak_saravanan on Monday 26th of July 2010 11:15:22 AM

07-26-2010

Registered User

Track Child process exit

hi,

I have a job that spawns multiple child processes in background.. Catch is i want to wait for some jobs to finish before i spawn more background processes. (each job creates a file and deletes at the end of it . so i don't want start new jobs after x amount of disk size is used up)

now, i setup trap
trap child_exit_handler CHLD
to increment and decrement a counter. but this traps executes only once for any number of child exits. Can somebody shed light what mistake i am doing. or a better way to do this.

here is my actual program.
I wanted to increment / decrement TOTAL_PROC variable . since i can't change this inside child job, i am trying to increment before child starts and decrement when child exits.

Code:

#!/bin/ksh
 
set -o monitor # must set to invoke CHLD signals
 
typeset -i TOTAL_PROC
function do_child
{
echo "ENTER CHILD $PPID with total  $TOTAL_PROC"
sleep 5
echo "Exit CHILD $PPID total $TOTAL_PROC "
exit 0
}
 
function child_exit_handler
{
echo "Enter child handler total $TOTAL_PROC "
(( TOTAL_PROC  -=  1 ))
echo "Exit child handler total $TOTAL_PROC "
}
 
TOTAL_PROC=0
 
LOOP_COUNT=0
MAX_COUNT=$1
 
typeset -x COPID=
 
echo "ENTER WHILE $$ at `date`"
 
while [[ $LOOP_COUNT < $MAX_COUNT  ]]; do
 
echo "LOOP IS $LOOP_COUNT , $MAX_COUNT"
 
(( TOTAL_PROC  += 1 ))
do_child  & COPID="$COPID $!"  # capture PID of coprocess
trap  child_exit_handler CHLD
 
echo "Inside while total $TOTAL_PROC "
(( LOOP_COUNT  += 1 ))
done
echo "Outside while total before wait $TOTAL_PROC "
 
wait
echo "Outside while total after wait $TOTAL_PROC "
echo "EXIT WHILE $$ at `date`"

ak_saravanan

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LEARN ABOUT BSD

fork

FORK(2) 							System Calls Manual							   FORK(2)

NAME

       fork - create a new process

SYNOPSIS

       pid = fork()
       int pid;

DESCRIPTION

       Fork causes creation of a new process.  The new process (child process) is an exact copy of the calling process except for the following:

	    The child process has a unique process ID.

	    The child process has a different parent process ID (i.e., the process ID of the parent process).

	    The child process has its own copy of the parent's descriptors.  These descriptors reference the same underlying objects, so that, for
	    instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the  child
	    process  can affect a subsequent read or write by the parent.  This descriptor copying is also used by the shell to establish standard
	    input and output for newly created processes as well as to set up pipes.

	    The child processes resource utilizations are set to 0; see setrlimit(2).

RETURN VALUE

       Upon successful completion, fork returns a value of 0 to the child process and returns the process ID of the child process  to  the  parent
       process.   Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
       indicate the error.

ERRORS

       Fork will fail and no child process will be created if one or more of the following are true:

       [EAGAIN]       The system-imposed limit on the total number of processes under execution would be exceeded.  This limit	is  configuration-
		      dependent.

       [EAGAIN]       The  system-imposed limit MAXUPRC (<sys/param.h>) on the total number of processes under execution by a single user would be
		      exceeded.

       [ENOMEM]       There is insufficient swap space for the new process.

SEE ALSO

       execve(2), wait(2)

3rd Berkeley Distribution					   May 22, 1986 							   FORK(2)

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