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Full Discussion: Controlling the Number of Child processes
Top Forums Shell Programming and Scripting Controlling the Number of Child processes Post 302922856 by APT_3009 on Tuesday 28th of October 2014 05:49:49 PM
Old 10-28-2014
Controlling the Number of Child processes
I am trying to implement the below using Ksh script on a Lx machine.

There is a file(input_file) with 100K records. For each of these records, certain script(process_rec) needs to be called with the record as input. Sequential processing is time-consuming and parallel processing would eat up resources.
I would like to ensure that at any given time there are exactly 10 processes running. The problem with using wait command is that it waits until all child processes are over.

For example - If first 10 records are being processed by 10 child processes, I would like that if any 1 of the child process completes, a new child process gets started processing the 11th record from the input_file.

How could this be achieved?
 

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LEARN ABOUT HPUX

waitid

waitid(2)							System Calls Manual							 waitid(2)

NAME

       waitid - wait for child process to change state

SYNOPSIS

DESCRIPTION

       The function suspends the calling process until one of its children changes state. It records the current state of a child in the structure
       pointed to by infop.  If a child process changed state prior to the call to returns immediately.

       The idtype and id arguments are used to specify which children will wait for.

       If idtype is will wait for the child with a process ID equal to (pid_t)pid.

       If idtypeis will wait for any child with a process group ID equal to (pid_t)pid.

       If idtypeis will wait for any children and id is ignored.

       The options argument is used to specify which state changes will wait for. It is formed by OR-ing together one or  more	of  the  following
       flags:

	      Wait for processes that have exited.

	      Status will be returned for any child that has stopped upon receipt
				       of a signal.

	      Status will be returned for any child that was stopped and has been
				       continued.

	      Return immediately if there  are	no children to wait for.

	      Keep the process whose status is returned in
				       infop  in  a  waitable  state. This will not affect the state of the process; the process may be waited for
				       again after this call completes.

       The infop argument must point to a structure. If returns because a child process was found that satisfied the conditions indicated  by  the
       arguments  idtype  and  options, then the structure pointed to by infop will be filled in by the system with the status of the process. The
       si_signo member will always be equal to

RETURN VALUE

       If returns due to the change of state of one of its children, 0 is returned. Otherwise, -1 is returned and is set to indicate the error.

ERRORS

       The function will fail if:

	      [ECHILD]	     The calling process has no existing unwaited-for child processes.

	      [EINTR]	     The function was interrupted due to the receipt of a signal by the calling process.

	      [EINVAL]	     An invalid value was specified for options, or idtype and id specify an invalid set of processes.

APPLICATION USAGE

   Threads Considerations
       In a multi-threaded application, only the calling thread is suspended by

       will not return until all threads in the process have reached the desired state.  For example, if the or options are  specified,  will  not
       return until all threads in the process have terminated, stopped or continued respectively.

SEE ALSO

       exec(2), exit(2), wait(2), <sys/wait.h>.

CHANGE HISTORY

       First released in Issue 4, Version 2.

																	 waitid(2)
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