LWP::Parallel::UserAgent chunk size

Posted on 2006-07-05
Medium Priority
Last Modified: 2012-06-21
I want to use LWP::Parallel::UserAgent to issue HTTP requests, and have the responses processed by a callback function. I want to process the whole response data at the same time, so I've set the chunk size to be very large (100 MB). I was thinking that this would make each chunk to be the whole page. However, that didn't work. Each chunk becomes about 1460 bytes anyway.

What could I be doing wrong? Is this a common problem?



use strict;
use LWP::Parallel::UserAgent;

my $ua = LWP::Parallel::UserAgent->new();
$ua->max_hosts(5); # sets maximum number of locations accessed in parallel
$ua->max_req(5); # sets maximum number of parallel requests per host

while(<>) #read in urls
        my $request = HTTP::Request->new(GET => $_);
        print $request;
        $ua->register($request, \&uaCallback, 100000000);

$ua->wait ();

sub uaCallback
        my($data, $response, $protocol) = @_;
        print "BASE: ", $response->base(), "\n";
        print "LENGTH: ", length($data), "\n";



echo "http://arctic.fws.gov/permglos.htm" | perl oneDeepCrawl.pl
HTTP::Request=HASH(0x8279c64)BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1159
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1448
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1448
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1484
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1448
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1448
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1484
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 2896
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 4380
BASE: http://arctic.fws.gov/permglos.htm
LENGTH: 1200
BASE: http://arctic.fws.gov/permglos.htm


Thanks again.
Question by:BerkeleyJeff
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LVL 20

Accepted Solution

jmcg earned 2000 total points
ID: 17055688
Why parallel if you're only interested in handling completed responses?

Alter your callback to accumulate the incoming data in the response object:

   if( length $data) { $response->add_content( $data); }

You will have to figure out the best way to determine when you've seen the last of the data so you can process it as a single chunk. Perhaps check whether

    $response->length > length( $response->content->as_string)


See this article by Randy Schwartz -- while it's old, it should not need much updating to re-use his methods:



Author Comment

ID: 17063227

Thanks for your response.

Perhaps I'm misunderstanding the purpose of ParallelUA. My goal was to download a large number different of pages simutaneously. Is this not what ParallelUA is for? Is ParallelUA for downloading a single page using multiple connections?
LVL 20

Expert Comment

ID: 17063362
Yep, parallel will help on getting through a longer list of pages. You only get one thread working per URL.

If you can get what you need from the responses without downloading them all the way to the end, it also can speed things up (using the C_ENDCON response from your callback).

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