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Top Forums Shell Programming and Scripting How to call a background process in perl? Post 302543492 by vanitham on Monday 1st of August 2011 03:08:55 AM
Old 08-01-2011
How to call a background process in perl?

Hi,

I want to put the following code as a parallel or background process

The program is as below:
Code:
$n=10; #Count of files to be created. 
for($j=0;$j<=$n;$j++) {
open(FH,">files_$j.txt") || warn "cannot create a file\n";
{
print FH "count of file: $j\n"; #Sample data to be written. just an example.
system("mv files_$j.txt /home/backup/remove/files") #put the following code as a parallel or background process
}
close FH;
}

Is it possible to make the "mv" command i.e. moving the files from current working directory to other directory
to be independent of the main code?

The first file gets created and then the MV command gets called and file gets transfered again the next file
gets created and MV command is called and so on. As a sample data i have given the count to be written what if
there is huge amount of data (around few GB) to be written and transferred. It takes quite large amount of time.

How can i make the file copying as an indepenent process?
file1 gets created -> MV is called as an background process
file 2 gets created but MV will be called in parallel not as a dependent process

File creation should not wait for the MV command as an background process?

How can i do it in Perl?

Regards
Vanitha
 

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Tcl_DetachPids(3)					      Tcl Library Procedures						 Tcl_DetachPids(3)

__________________________________________________________________________________________________________________________________________________

NAME
Tcl_DetachPids, Tcl_ReapDetachedProcs, Tcl_WaitPid - manage child processes in background SYNOPSIS
#include <tcl.h> Tcl_DetachPids(numPids, pidPtr) Tcl_ReapDetachedProcs() Tcl_Pid Tcl_WaitPid(pid, statusPtr, options) ARGUMENTS
int numPids (in) Number of process ids contained in the array pointed to by pidPtr. int *pidPtr (in) Address of array containing numPids process ids. Tcl_Pid pid (in) The id of the process (pipe) to wait for. int *statusPtr (out) The result of waiting on a process (pipe). Either 0 or ECHILD. int options (in) The options controlling the wait. WNOHANG specifies not to wait when checking the process. _________________________________________________________________ DESCRIPTION
Tcl_DetachPids and Tcl_ReapDetachedProcs provide a mechanism for managing subprocesses that are running in background. These procedures are needed because the parent of a process must eventually invoke the waitpid kernel call (or one of a few other similar kernel calls) to wait for the child to exit. Until the parent waits for the child, the child's state cannot be completely reclaimed by the system. If a parent continually creates children and doesn't wait on them, the system's process table will eventually overflow, even if all the children have exited. Tcl_DetachPids may be called to ask Tcl to take responsibility for one or more processes whose process ids are contained in the pidPtr array passed as argument. The caller presumably has started these processes running in background and does not want to have to deal with them again. Tcl_ReapDetachedProcs invokes the waitpid kernel call on each of the background processes so that its state can be cleaned up if it has exited. If the process has not exited yet, Tcl_ReapDetachedProcs does not wait for it to exit; it will check again the next time it is invoked. Tcl automatically calls Tcl_ReapDetachedProcs each time the exec command is executed, so in most cases it is not necessary for any code outside of Tcl to invoke Tcl_ReapDetachedProcs. However, if you call Tcl_DetachPids in situations where the exec command may never get executed, you may wish to call Tcl_ReapDetachedProcs from time to time so that background processes can be cleaned up. Tcl_WaitPid is a thin wrapper around the facilities provided by the operating system to wait on the end of a spawned process and to check a whether spawned process is still running. It is used by Tcl_ReapDetachedProcs and the channel system to portably access the operating sys- tem. KEYWORDS
background, child, detach, process, wait Tcl Tcl_DetachPids(3)
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