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Re: Proper way to thread this in PERL.

by Preceptor (Chaplain)
on Dec 25, 2013 at 23:34 UTC ( #1068378=note: print w/ replies, xml ) Need Help??


in reply to Proper way to thread this in PERL.

I would strongly suggest avoiding spawning new threads in a 'while' loop. That just causes you grief. Each time you 'create' a thread, it copies your program state, which becomes a particular problem when you're loading lots of modules. Instead, I would advocate a 'worker thread' approach, and use Thread::Queue to 'feed' them.

my $url_q = Thread::Queue -> new(); sub http_fetch_thread { my $ua = LWP::UserAgent -> new(); $ua -> timeout ( 10 ); while ( my $item = $url_q -> dequeue() ) { my $url = "http://www." . $item . ".com"; <... fetch stuff ... > } }

Spawn a defined number of these threads (you look like you're trying to keep to 5?) and then just feed the contents of your file, into '$url_q'.

for ( 1..$thrCount ) { threads -> create ( \&http_fetch_thread ); } open ( my $contents, "<", $contents_file_name ) or die $!; $url_q -> enqueue ( <$contents> ); $url_q -> end; close ( $contents ); #wait for completion foreach my $thr ( threads -> list() ) { $thr -> join(); #not capturing return code, we started in a void con +text. } print "At program completion, total count was ", $totalCount,"\n";

So rather than starting a new thread every line of your file, which is instantiating a new 'useragent' object, you'll create a number equal to the number of threads defined - and then run through the list as fast as they can, and probably won't chew up your memory anything like as badly (and because you're not creating/destroying useragents and threads, you'll probably find it runs a lot faster too).

If you want a running total of 'totalCount' you can either print it from within the thread, or instead of doing the 'foreach/join' loop, do a 'while' loop:

while ( threads -> list ) { foreach my $thread ( threads -> list ( threads::joinable ) ) { $thread -> join(); } print $totalCount,"\n"; sleep 5; }

Edit: More generally I'd suggest:

  • 3 argument 'opens' are nicer, especially when threading. (When is 'CONTENT' in scope?)
  • Detaching a thread can mean your program completing without the thread finishing. That can create anomalous results, so I'd suggest avoiding it generally
  • Parsing '@ARGV' by hand is a good way to introduce bugs. Look at GetOpt::Std for anything more than very trivial cases.


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Re^2: Proper way to thread this in PERL.
by tekio (Novice) on Dec 26, 2013 at 01:46 UTC
    These are excellent replies! Thank you guys so much! :)

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