/ 
Sub-Throttler-v0.2.10
River stage one • 1 direct dependent • 1 total dependent
/ Sub::Throttler::Limit

NAME

Sub::Throttler::Limit - throttle by quantity

VERSION

This document describes Sub::Throttler::Limit version v0.2.10

SYNOPSIS

use Sub::Throttler::Limit;

my $throttle = Sub::Throttler::Limit->new(limit => 5);

$throttle->apply_to_methods(Mojo::UserAgent => qw( get post ));

DESCRIPTION

This is a plugin for Sub::Throttler providing simple algorithm for throttling by quantity of used resources.

In a nutshell it's just a hash, with resource names as keys and currently used resource quantities as values; plus one limit on maximum quantity applied to any key. Of course, each instance will have own hash/limit.

When you configure it you define which functions/methods it should throttle, and which resource name(s) and quantity(ies) of that resource(s) each function/method should acquire to run.

In basic use case you'll use one instance and configure it using "apply_to_functions" in Sub::Throttler::algo and/or "apply_to_methods" in Sub::Throttler::algo helpers - which result in any throttled function/method will need 1 resource named "default" to run. This way you'll effectively use just one counter, which will increase when any throttled function/method run and decrease when it finish, so you will have up to limit simultaneously running functions/methods (limit is usually set when you call "new").

my $throttle_tasks = Sub::Throttler::Limit->new(limit => 5);
$throttle_tasks->apply_to_functions('run_background_task');
# This code will start 5 background tasks but last two will be
# put into queue instead of being started. When any of started
# background tasks will finish first one of queued tasks will be
# started, etc. Usually you'll need event loop or something else
# to make this really works, but this has nothing with throttling.
for (1..7) {
    run_background_task();
}
# this function must support throttling
sub run_background_task { ... }

In advanced use case you may use many counters in one instance (by using "apply_to" in Sub::Throttler::algo to define different resource names/quantities for different throttled functions/methods) and have many instances (with different limit) throttling same or different functions/methods.

my $throttle_tasks = Sub::Throttler::Limit->new(limit => 5);
my $throttle_cpu   = Sub::Throttler::Limit->new(limit => 100);
# allow to simultaneously run up to 5 side_task() plus up to:
# - 5 small_task() or
# - 2 normal_task() plus 1 small_task() or
# - 1 large_task() plus 1 normal_task() or
# - 1 large_task() plus 2 small_task()
$throttle_tasks->apply_to(sub {
    my ($this, $name, @param) = @_;
    if ($name eq 'small_task') {
        return { task => 1 };
    } elsif ($name eq 'normal_task') {
        return { task => 2 };
    } elsif ($name eq 'large_task') {
        return { task => 3 };
    } elsif ($name eq 'side_task') {
        return { side => 1 };
    }
    return;
});
# and apply extra limitation on amount of simultaneously running
# side_task() depending on it first parameter (number between 1 and
# 100 showing how much CPU this side_task() will use)
$throttle_cpu->apply_to(sub {
    my ($this, $name, @param) = @_;
    if ($name eq 'side_task') {
        return { default => $param[0] };
    }
    return;
});
# here is how it will works:
large_task();   # started ($throttle_tasks 'task' == 3)
side_task(60);  # started ($throttle_tasks 'side' == 1,
                #          $throttle_cpu 'default' == 60)
small_task();   # started ($throttle_tasks 'task' == 4)
normal_task();  # delayed ($throttle_tasks 'task' + 2 > limit)
side_task(30);  # started ($throttle_tasks 'side' == 2,
                #          $throttle_cpu 'default' == 90)
side_task(30);  # delayed ($throttle_cpu 'default' + 30 > limit)

EXPORTS

Nothing.

INTERFACE

Sub::Throttler::Limit inherits all methods from Sub::Throttler::algo and implements the following ones.

new

my $throttle = Sub::Throttler::Limit->new;
my $throttle = Sub::Throttler::Limit->new(limit => 42);

Create and return new instance of this algorithm.

Default limit is 1.

See "new" in Sub::Throttler::algo for more details.

limit

my $limit = $throttle->limit;
$throttle = $throttle->limit(42);

Get or modify current limit.

load

my $throttle = Sub::Throttler::Limit->load($state);

Create and return new instance of this algorithm.

Only limit is restored. Information about acquired resources won't be restored because there is no way to release these resources later.

See "load" in Sub::Throttler::algo for more details.

save

my $state = $throttle->save();

Return current state of algorithm needed to restore it using "load" after application restart.

See "save" in Sub::Throttler::algo for more details.

SUPPORT

Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker at https://github.com/powerman/perl-Sub-Throttler/issues. You will be notified automatically of any progress on your issue.

Source Code

This is open source software. The code repository is available for public review and contribution under the terms of the license. Feel free to fork the repository and submit pull requests.

https://github.com/powerman/perl-Sub-Throttler

git clone https://github.com/powerman/perl-Sub-Throttler.git

Resources

AUTHOR

Alex Efros <powerman@cpan.org>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2014- by Alex Efros <powerman@cpan.org>.

This is free software, licensed under:

The MIT (X11) License