Initial implementation

.gitignore

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+Gemfile.lock
+pkg/

Gemfile

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+source :rubygems
+gemspec

LICENSE.txt

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+Copyright (c) 2013 brainopia
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+## Description
+
+Sidekig strategy to restrict number of workers
+which are able to run specified queues simultaneously.
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+    gem 'sidekiq-limit_fetch'
+
+## Usage
+
+Specify limits which you want to place on queues inside sidekiq.yml:
+
+```yaml
+:limits:
+  restricted_queue: 5
+```
+
+In this example, tasks for restricted queue will be run by at most 5
+workers at the same time.

Rakefile

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+require "bundler/gem_tasks"

lib/sidekiq/limit_fetch.rb

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+require 'sidekiq'
+
+class Sidekiq::LimitFetch
+  require_relative 'limit_fetch/semaphore'
+  require_relative 'limit_fetch/queue'
+  require_relative 'limit_fetch/unit_of_work'
+
+  Sidekiq.options[:fetch] = self
+
+  def initialize(options)
+    prepare_queues options
+    options[:strict] ? define_strict_queues : define_weighted_queues
+  end
+
+  def available_queues
+    fetch_queues.select(&:acquire)
+  end
+
+  def retrieve_work
+    queues = available_queues
+    queue_name, message = Sidekiq.redis do |it|
+      it.brpop *queues.map(&:full_name), Sidekiq::Fetcher::TIMEOUT
+    end
+
+    if message
+      queue = queues.find {|it| it.name == queue_name }
+      queues.delete queue
+
+      UnitOfWork.new queue, message
+    end
+  ensure
+    queues.each(&:release) if queues
+  end
+
+  private
+
+  def prepare_queues(options)
+    cache = {}
+    limits = options[:limits] || {}
+
+    @queues = options[:queues].map do |name|
+      cache[name] ||= Queue.new name, limits[name]
+    end
+  end
+
+  def define_strict_queues
+    @queues.uniq!
+    def fetch_queues
+      @queues
+    end
+  end
+
+  def define_weighted_queues
+    def fetch_queues
+      @queues.shuffle.uniq
+    end
+  end
+end

lib/sidekiq/limit_fetch/queue.rb

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+class Sidekiq::LimitFetch
+  class Queue
+    extend Forwardable
+
+    attr_reader :name, :full_name
+    def_delegators :@lock, :acquire, :release
+
+    def initialize(name, limit)
+      @name = name
+      @full_name = "queue:#{name}"
+      @lock = Semaphore.for limit
+    end
+  end
+end

lib/sidekiq/limit_fetch/semaphore.rb

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+class Sidekiq::LimitFetch::Semaphore
+  Stub = Struct.new(:acquire, :release)
+
+  def self.for(limit)
+    limit ? new(limit) : stub
+  end
+
+  def self.stub
+    @stub ||= Stub.new(true, true)
+  end
+
+  def initialize(limit)
+    @lock  = Mutex.new
+    @limit = limit
+  end
+
+  def acquire
+    @lock.synchronize do
+      @limit -= 1 if @limit > 0
+    end
+  end
+
+  def release
+    @lock.synchronize do
+      @limit += 1
+    end
+  end
+end

lib/sidekiq/limit_fetch/unit_of_work.rb

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+Sidekiq::LimitFetch::UnitOfWork = Struct.new :queue_wrapper, :message do
+  extend Forwardable
+
+  def_delegator :queue_wrapper, :full_name, :queue
+  def_delegator :queue_wrapper, :name, :queue_name
+  def_delegator :queue_wrapper, :release
+
+  def acknowledge
+    release
+  end
+
+  def requeue
+    release
+    Sidekiq.redis {|it| it.rpush queue, message }
+  end
+end

sidekiq-limit_fetch.gemspec

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+Gem::Specification.new do |gem|
+  gem.name          = 'sidekiq-limit_fetch'
+  gem.version       = '0.1'
+  gem.authors       = 'brainopia'
+  gem.email         = 'brainopia@evilmartians.com'
+  gem.summary       = 'Sidekig strategy to support queue limits'
+  gem.homepage      = 'https://github.com/brainopia/sidekiq-limit_fetch'
+  gem.description   = <<-DESCRIPTION
+    Sidekig strategy to restrict number of workers
+    which are able to run specified queues simultaneously.
+  DESCRIPTION
+
+  gem.files         = `git ls-files`.split($/)
+  gem.test_files    = gem.files.grep %r{^spec/}
+  gem.require_paths = %w(lib)
+
+  gem.add_dependency 'sidekiq', '>= 2.6.3'
+  gem.add_development_dependency 'rspec'
+end