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Think about Loose Coupling

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Hi again perlygapes,

The MCE::Loop code just abstracts away all your Parallel::ForkManager logic and improves it, just as Parallel::ForkManager abstracts away and improves some of the tedious manual work of using fork() directly. See how the logic is encapsulated in a sub just like in your code, only with less concurrency boilerplate.

"using a separate DB connection instead for each child feels intuitively right"

I agree, the code I shared keeps a connection open for each child, which itself stays alive and handles multiple jobs from the job list as managed by MCE.

Here's a simpler example I've shared recently showing how to parallelize existing code for making a series of HTTP requests. How would you do the same using P::FM?

single process

use strict; use warnings; use 5.010; use Data::Dumper; use HTTP::Tiny; use Time::HiRes 'gettimeofday', 'tv_interval'; my $ua = HTTP::Tiny->new( timeout => 10 ); my @urls = qw< >; my %report; foreach( @urls) { my $start = [gettimeofday]; $ua->get('https://' . $_); $report{$_} = tv_interval($start, [gettimeofday]) ); }); say Dumper \%report;

six processes
(workers stay alive, looping through the list, writing to a shared hash)
(one added line, two slightly changed lines)

use strict; use warnings; use 5.010; use Data::Dumper; use HTTP::Tiny; use Time::HiRes 'gettimeofday', 'tv_interval'; use MCE; use MCE::Shared; my $ua = HTTP::Tiny->new( timeout => 10 ); my @urls = qw< >; my $report = MCE::Shared->hash; MCE->new( max_workers => 6 )->foreach( \@urls, sub { my $start = [gettimeofday]; $ua->get('https://' . $_); $report->set( $_, tv_interval($start, [gettimeofday]) ); }); say Dumper $report->export;

Update: fixed error in first demo code, ++choroba

Hope this helps!

The way forward always starts with a minimal test.

In reply to Re^3: Create parallel database handles... (MCE::Loop) by 1nickt
in thread Create parallel database handles or SQL statements for multi-threaded/process access to Postgres DB using DBI, DBD::Pg and Parallel::ForkManager by perlygapes

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