First implementation

.gitignore

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+/.bundle/
+/.yardoc
+/Gemfile.lock
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+
+# rspec failure tracking
+.rspec_status

.rspec

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+--format documentation
+--color

.travis.yml

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+sudo: false
+language: ruby
+
+rvm:
+  - 2.4.1
+
+before_install:
+  - curl -sL https://dl.google.com/dl/cloudsdk/channels/rapid/google-cloud-sdk.tar.gz | tar xz
+  - google-cloud-sdk/install.sh --override-components beta pubsub-emulator --quiet
+  - export PATH=$PATH:$PWD/google-cloud-sdk/bin

Gemfile

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+source 'https://rubygems.org'
+
+gemspec
+
+gem 'concurrent-ruby-ext'

LICENSE.txt

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+The MIT License (MIT)
+
+Copyright (c) 2017 Keita Urashima
+
+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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+# ActiveJob::GoogleCloudPubsub
+
+Google Cloud Pub/Sub adapter and worker for ActiveJob
+
+## Installation
+
+```ruby
+gem 'activejob-google_cloud_pubsub'
+```
+
+## Usage
+
+First, change the ActiveJob backend.
+
+``` ruby
+Rails.application.config.active_job.queue_adapter = :google_cloud_pubsub
+```
+
+Write the Job class and code to use it.
+
+``` ruby
+class HelloJob < ApplicationJob
+  def perform(name)
+    puts "hello, #{name}!"
+  end
+end
+```
+
+``` ruby
+class HelloController < ApplicationController
+  def say
+    HelloJob.perform_later params[:name]
+  end
+end
+```
+
+In order to test the worker in your local environment, it is a good idea to use the Pub/Sub emulator provided by `gcloud` command. Refer to [this document](https://cloud.google.com/pubsub/docs/emulator) for the installation procedure.
+
+When the installation is completed, execute the following command to start up the worker.
+
+``` sh
+$ gcloud beta emulators pubsub start
+
+(Switch to another terminal)
+
+$ eval `gcloud beta emulators pubsub env-init`
+$ cd path/to/your-app
+$ bundle exec activejob-google_cloud_pubsub-worker
+```
+
+If you hit the previous action, the job will be executed.
+(Both the emulator and the worker stop with <kbd>Ctrl+C</kbd>)
+
+## Configuration
+
+### Adapter
+
+When passing options to the adapter, you need to create the object instead of a symbol.
+
+``` ruby
+Rails.application.config.active_job.queue_adapter = ActiveJob::QueueAdapters::GoogleCloudPubsubAdapter.new(options)
+```
+
+All options are passed to [`Google::Cloud::Pubsub.new`](http://googlecloudplatform.github.io/google-cloud-ruby/#/docs/google-cloud-pubsub/v0.23.2/google/cloud/pubsub?method=new-class).
+
+### Worker
+
+The following command line flags can be specified. All flags are optional.
+
+#### `--require=PATH`
+
+The path of the file to load before the worker starts up.
+
+Default: `./config/environment`
+
+#### `--queue=NAME`
+
+The name of the queue the worker handles.
+
+Note: One worker can handle only one queue. If you use multiple queues, you need to launch multiple worker processes.
+
+Default: `default`
+
+#### `--min_threads=N`
+
+Minimum number of worker threads.
+
+Default: `0`
+
+#### `--max_threads=N`
+
+Maximum number of worker threads.
+
+Default: number of logical cores
+
+#### `--project=PROJECT_ID`, `--keyfile=PATH`
+
+Credentials of Google Cloud Platform. Please refer to [the document](https://github.com/GoogleCloudPlatform/google-cloud-ruby/blob/master/AUTHENTICATION.md) for details.
+
+``` sh
+$ bundle exec rake spec
+```
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/ursm/activejob-google_cloud_pubsub.
+
+## License
+
+The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).

Rakefile

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+require 'bundler/gem_tasks'
+require 'rspec/core/rake_task'
+
+RSpec::Core::RakeTask.new(:spec)
+
+task :default => :spec

activejob-google_cloud_pubsub.gemspec

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+lib = File.expand_path('../lib', __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+require 'active_job/google_cloud_pubsub/version'
+
+Gem::Specification.new do |spec|
+  spec.name          = 'activejob-google_cloud_pubsub'
+  spec.version       = ActiveJob::GoogleCloudPubsub::VERSION
+  spec.authors       = ['Keita Urashima']
+  spec.email         = ['[email protected]']
+
+  spec.summary       = 'Google Cloud Pub/Sub adapter and worker for ActiveJob'
+  spec.homepage      = 'https://github.com/ursm/activejob-google_cloud_pubsub'
+  spec.license       = 'MIT'
+
+  spec.files         = `git ls-files -z`.split("\x0").reject do |f|
+    f.match(%r{^(test|spec|features)/})
+  end
+
+  spec.bindir        = 'exe'
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ['lib']
+
+  spec.add_runtime_dependency 'activejob'
+  spec.add_runtime_dependency 'activesupport'
+  spec.add_runtime_dependency 'concurrent-ruby'
+  spec.add_runtime_dependency 'google-cloud-pubsub'
+
+  spec.add_development_dependency 'bundler'
+  spec.add_development_dependency 'rake'
+  spec.add_development_dependency 'rspec'
+end

bin/console

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+#!/usr/bin/env ruby
+
+require 'bundler/setup'
+require 'activejob-google_cloud_pubsub'
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+# (If you use this, don't forget to add pry to your Gemfile!)
+# require "pry"
+# Pry.start
+
+require 'irb'
+IRB.start(__FILE__)

bin/setup

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+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here

exe/activejob-google_cloud_pubsub-worker

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+#!/usr/bin/env ruby
+
+require 'activejob-google_cloud_pubsub'
+require 'google/cloud/pubsub'
+require 'optparse/kwargs'
+
+Version = ActiveJob::GoogleCloudPubsub::VERSION
+
+args = {
+  require: './config/environment'
+}
+
+opt = OptionParser.new
+
+opt.on '--[no-]require=PATH' do |v|
+  args[:require] = v
+end
+
+worker_args = opt.define_by_keywords(
+  {},
+  ActiveJob::GoogleCloudPubsub::Worker.instance_method(:initialize),
+  {
+    min_threads: Integer,
+    max_threads: Integer
+  }
+)
+
+pubsub_args = opt.define_by_keywords(
+  {},
+  Google::Cloud::Pubsub.method(:new),
+  {
+    scope:   Array,
+    timeout: Integer
+  }
+)
+
+opt.parse ARGV
+
+require args[:require] if args[:require]
+
+ActiveJob::GoogleCloudPubsub::Worker.new(**worker_args, **pubsub_args).run

lib/active_job/google_cloud_pubsub/adapter.rb

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+require 'active_job/google_cloud_pubsub/naming'
+require 'google/cloud/pubsub'
+require 'json'
+
+module ActiveJob
+  module GoogleCloudPubsub
+    class Adapter
+      include Naming
+
+      def initialize(**pubsub_args)
+        @pubsub = Google::Cloud::Pubsub.new(pubsub_args)
+      end
+
+      def enqueue(job, attributes = {})
+        topic = @pubsub.topic(topic_name(job.queue_name), autocreate: true)
+
+        topic.publish JSON.dump(job.serialize), attributes
+      end
+
+      def enqueue_at(job, timestamp)
+        enqueue job, timestamp: timestamp
+      end
+    end
+  end
+end
+
+require 'active_job'
+
+ActiveJob::QueueAdapters::GoogleCloudPubsubAdapter = ActiveJob::GoogleCloudPubsub::Adapter

lib/active_job/google_cloud_pubsub/naming.rb

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+module ActiveJob
+  module GoogleCloudPubsub
+    module Naming
+      def topic_name(queue_name)
+        "activejob-queue-#{queue_name}"
+      end
+
+      def subscription_name(queue_name)
+        "activejob-worker-#{queue_name}"
+      end
+    end
+  end
+end

lib/active_job/google_cloud_pubsub/version.rb

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+module ActiveJob
+  module GoogleCloudPubsub
+    VERSION = '0.1.0'
+  end
+end