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Re^2: Need help with Perl multi threading

by BrowserUk (Pope)
on Jan 26, 2012 at 16:20 UTC ( #950156=note: print w/replies, xml ) Need Help??

in reply to Re: Need help with Perl multi threading
in thread Need help with Perl multi threading

I would be hard-pressed to be convinced that “adding threads to” such an algorithm that is right now “working fine(!)” will actually make it either more reliable, or faster.

Perhaps if you relied less on your apparently limited imagination and tried using the stuff you feel obliged to talk about, you might talk less crap.

Threading always divides time, while adding considerable complication.

What!? What on earth are you taking when you dream this stuff up? I mean really man, did you do no simple math at school:

One man digs a ditch and it takes 8 hours. Two men dig another identical ditch and it takes 4.

... or were you simply to busy bullshitting about how you'd seen and done it all in pre-school, to take any notice.

So, all kinds of Danger, Will Robinson! alarm bells are going off in my head.

Geez! You're like a kid that was told masturbation would make him go blind and has refused wash his winkle ever since.

A simple example of threading at work:

Fetching 100 urls serially:

#! perl -slw use strict; use LWP::Simple; my $start = time; while( <> ) { chomp; eval { local $SIG{ ALRM } = sub { die 'timeout' }; alarm 10; my($content_type, $document_length, $modified_time, $expires, +$server) = head( "http://$_" ) or warn "Failed to HEAD $_: $!\n"; }; } printf "\nRunning HEAD on $. urls serially took %d seconds\n", time() - $start; __END__ C:\test>junk57 urls.list.small Failed to HEAD Bad file descriptor Failed to HEAD Bad file descriptor Failed to HEAD Bad file descriptor Running HEAD on 100 urls serially took 102 seconds

Fetching those same urls in parallel:

#! perl -slw use strict; use threads; use LWP::Simple; my $start = time; my @threads; while( <> ) { chomp; push @threads, async{ eval { local $SIG{ ALRM } = sub { die 'timeout' }; alarm 10; my( $content_type, $document_length, $modified_time, $expi +res, $server ) = head( "http://$_" ) or warn "Failed to HEAD $_: $!\n"; }; }; } $_->join for @threads; printf "\nRunning HEAD on $. urls using threading took %d seconds\n", time() - $start; __END__ C:\test>junk58 urls.list.small Failed to HEAD Failed to HEAD Failed to HEAD Running HEAD on 100 urls using threading took 19 seconds

5 times faster -- and look at how much more complicated it is. Four whole extra lines!

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

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[choroba]: Spreading the word...
[hippo]: Nice!

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