Re: Fork and wait question

Just screwing around.... but I thought of using a piped open as an easy fork-an-exec. One problem, the filehandle in a hash won't print out. Anyone know why? Would this type of approach work?

#!/usr/bin/perl
use warnings;
use strict;

my %pids;

my @to_be_processed = (1..20);

my $cmd = 'echo';

foreach my $p (@to_be_processed){ 
   $pids{$p}{'pid'} = open($pids{$p}{'fh'}, "$cmd $p 2>&1 |");
}

# get output dosn't work? get globs
foreach my $key(keys %pids){ 
   while (<{ $pids{$key}{'fh'} }>){print $_}
}


foreach my $key(keys %pids){
   waitpid($pids{$key}, 1);
}

print "done\n";
[download]

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Comment on Re: Fork and wait question Download Code

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Re^2: Fork and wait question by samtregar (Abbot) on Jun 12, 2008 at 18:51 UTC
The `<>` operator is super fussy due to being overloaded with ancient glob() craziness. It only works if you put in a simple scalar, not any kind of expression. This works: `my $fh = $pids{$key}{'fh'}; while (<$fh>){print $_}` [download] This kind of thing will work fine until your sub-processes need to produce more than 4k of data (or whatever your buffer size is). Then the sub-procs will block when they print() and won't work in parallel while you're collecting results. To fix this you need to switch to using something like IO::Select or EV to pull data from each process as it's ready. -sam	[reply] [d/l] [select]
Re^2: Fork and wait question by pc88mxer (Vicar) on Jun 12, 2008 at 18:33 UTC
Calling `close` on the file handles will also wait for the processes to complete.	[reply] [d/l]
Re^3: Fork and wait question by chris68805 (Initiate) on Jun 12, 2008 at 18:41 UTC
Where do you put the close for the file handlers?	[reply]
Re^4: Fork and wait question by pc88mxer (Vicar) on Jun 12, 2008 at 19:05 UTC
Use it instead of the waitpid call: `foreach my $key(keys %pids){ close $pids{$key}{'fh'}; }` [download]	[reply] [d/l]