Await / Async

Add await and async keywords to Crystal.

Installation

In your shards.yml:

dependencies:
  await_async:
    github: anykeyh/await_async
    branch: master

Then:

require "await_async"

future = async fetch_something

do_some_computation_now

await future

Usage

• Call async on any method or block to create a MiniFuture
• Call await on any MiniFuture to wait for/get the result
• Conveniently, you can call await on future's array.

Can improve drastically application which relay on blocking IO like web API or file writing.

await(timeout, future)

future = async check_website

begin
  await 5.seconds, future
rescue MiniFuture::TimeoutException
  # rescue from timeout
end

async! / async

By default, async! call the newly created fiber just after creation.

• You can use instead async so the fiber won't start now:

future = async! { 1 + 2 }
# At this moment the result is already computed
# future.finished? == true
await future # => 3

# vs

future = async { 1 + 2 }
# Here the result is not computed
# future.finished? == false
await future # Compute now

Usually, use async if your block is computation intensive and current thread has IO blocking operation. Use async! in other cases.

In case of errors, the exception will be raise at await moment, in the await thread.

MiniFuture

A minimalist version of future. Has finished? and running? methods.

I don't use Crystal's Concurrent::Future class because :nodoc:.

Why?

Because crystal is great for building CLI tools. And CLI deals a lot with files and sockets. And IO performed in main thread are slow.

Usage of Channel is recommended for complex software, as it offers more patterns.

await/async is useful to build fast and deliver fast.

I don't want await/async to be exported in the global scope

1. require await_async/helper instead of await_async
2. In the class/module you want to use the methods, add include AwaitAsync::Helper. You can also simply call await/async directly from AwaitAsync::Helper

Example

def fetch_websites_async
  %w[
    www.github.com
    www.yahoo.com
    www.facebook.com
    www.twitter.com
    crystal-lang.org
  ].map do |url|
    async! do
      HTTP::Client.get "https://#{url}"
    end
  end
end

# Process the websites concurrently. Start querying another website when the
# first one is waiting for response
await(5.seconds, fetch_websites_async).each do |response|
  # ...
end

License

MIT