On Jun 24, 12:15 am, nora.hac...@stgkk.at ("HACKER Nora") wrote:
> Hi list,
>
> I am currently having an issue with background processes. I already
> searched the web and found a way how to principally send a process into
> background, wait for the execution to finish and then go on with the
> main program:
>
> my $pid = fork;
> if ( $pid ) {
> wait;
> print "done.\n";} else {
>
> print "starting.\n";
> system "compress *.dbf &";
> exit;
>
> }
>
> The "done." is being issued at the correct point of time, namely when
> really all files have been compressed. Unfortunately, this only
> compresses one file after the other and therefore lacks performance. So
> I tried to send multiple processes into background and have them to be
> executed simultaneously. I tried the following:
>
> my $pid = fork;
> if ( $pid ) {
> wait;
> print "done.\n";} else {
>
> print "starting.\n";
> foreach ( glob "*.dbf" ) {
> system "compress $_ &";
> exit;
>
> }
>
> This behaves as expected, from the "simultaneous" and "background" point
> of view - but my big problem is now that the message "done." is being
> issued as soon as all the compression processes are ISSUED instead of
> when they are FINISHED.
>
> Could anybody please point me into the right direction how to best solve
> that issue? Maybe I should fork all the single compression processes to
> get a pid for each, put them into an array and check with a loop whether
> they still exist (process running)? Would there be another / easier /
> more efficient way?
>
The backgrounding makes this harder because the system()
call will return immediately even if the backgrounded process
is still running. You can reap the b/g processes with an async
waitpid (see: perldoc -f waitpid. Also perldoc perlipc) but this
is a bit tricky and you'll need to to poll for completion with a
messy sleep-loop of some kind.
So I'd ditto the recommendation for Parallel::ForkManager
which'll background the tasks and also provides a method
'set_max_procs' to avoid hogging the system.
Another possibility, if impact to system isn't a concern, is
IPC::Run which'll background the tasks and handle other
messy details for you.
use IPC::Run qw/start finish/;
use strict;
use warnings;
my @cmds;
# Or easier on the system, wrap rest of code in a loop
# to process only some max. no. of files at a time
foreach ( glob "*.dbf" ) {
push @cmds, [ compress => $_ ];
}
my $harness = start map { ($_, '&') } @cmds;
$harness->finish or die "finish error: $?";
print "done...\n";
__END__
--
Charles DeRykus
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