Re: Parallel DNS queries (use threads; )

[BrowserUk]

TIMTOWTDI --

#! perl -slw
use strict;
use threads qw[ async ];
use Thread::Queue;

my @dnss = qw(
    111.111.111.111
    222.222.222.222
    111.222.111.222
    222.111.222.111
);

my $Q = new Thread::Queue;
my $host = $ARGV[ 0 ];

my $count : shared = @dnss;
async{ 
    $Q->enqueue( qx[ nslookup -type=A $host $_ 2>nul ] );
    $count--;
} for @dnss;

sleep 1 while $count; 
## Do something with results
print $Q->dequeue while $Q->pending;

[nothingmuch]

The semaphores provided with perl's threading modules should provide a nicer solution than sleep 1 while $count.

[BrowserUk]

Why write 30 lines of complicated code when one is just about perfect.

sleep causes the sleeping thread to relinguish its timeslice(s) until the sleep times out, which means almost no load.

The semaphores api (like the rest of the pthreads api that perls threads are modelled on), is under specified, messy and hard to get right.

The sleep 1 while $count; is easy to code, easy to understand and "just works" :)

[nothingmuch]

The one reason i wouldn't use it is because it's limited to 1 second granuality. But i'm one of those damned perfectionist. As for the API, since 5.8.0 there is one way to do it - nothing shared, and I don't like my threads like that. So i don't remember what it's like, but that's a good reason not to use them in the example.

For the record, the main reason I commented was in the hopes that you add a

     sleep 1 while $count; # Or use Thread::Semaphore

so that people who don't know about threads wouldn't think that's the only way. I guess I should have been more polite or something... =)