rb:async-patterns

Async Patterns

Fiber-based concurrency for Ruby using the async gem.

Overview

The async gem provides fiber-based concurrency:

Approach	Use Case	Concurrency Model
Threads	CPU-bound work	OS threads
Async	I/O-bound work	Fibers (lightweight)
Processes	Isolation	Fork/spawn

Use async when:

• Making many HTTP requests
• Reading from multiple files/streams
• Database queries that can run in parallel
• WebSocket handling
• High-concurrency I/O

Installation

# Gemfile
gem 'async'
gem 'async-http'       # HTTP client
gem 'async-io'         # I/O operations
gem 'falcon'           # Async web server (optional)

# Rails integration
gem 'async-job'        # Async job processor
gem 'async-cable'      # Async Action Cable (optional)

Basic Async

Simple Task

require 'async'

Async do |task|
  task.sleep(1)
  puts "Done!"
end

Concurrent Operations

require 'async'

Async do |task|
  # Spawn multiple concurrent tasks
  tasks = []
  
  tasks << task.async do
    task.sleep(1)
    "Task 1 done"
  end

  tasks << task.async do
    task.sleep(0.5)
    "Task 2 done"
  end

  tasks << task.async do
    task.sleep(1.5)
    "Task 3 done"
  end
  
  # Wait for all and get results
  results = tasks.map(&:wait)
  puts results
  # Total time: ~1.5s (not 3s!)
end

Error Handling

Async do |task|
  tasks = []
  
  tasks << task.async do
    raise "Task 1 failed"
  end
  
  tasks << task.async do
    "Task 2 success"
  end
  
  results = tasks.map do |t|
    begin
      t.wait
    rescue => e
      { error: e.message }
    end
  end
  
  puts results
  # => [{:error=>"Task 1 failed"}, "Task 2 success"]
end

Concurrent HTTP Requests

Using async-http

require 'async'
require 'async/http/internet'

Async do |task|
  internet = Async::HTTP::Internet.new
  
  # Fetch multiple URLs concurrently
  responses = []
  
  urls = [
    'https://api.example.com/users',
    'https://api.example.com/products',
    'https://api.example.com/orders'
  ]
  
  urls.each do |url|
    responses << task.async do
      response = internet.get(url)
      [url, response.read]
    end
  end
  
  # Wait for all responses
  data = responses.map(&:wait)
  
  # Process results
  data.each do |url, body|
    puts "#{url}: #{body.length} bytes"
  end
  
  internet.close
end