Is this logging appropriate?

[jesseduffield]

I'm seeing some warnings in my tests about tasks that 'may have ended with unhandled exception.'

I can't tell if this is async being overly cautious, or if I'm actually doing something wrong. As far as I can tell, this code is correct:

Code:

    def async_map(items:, concurrency_limit: Float::INFINITY, &block)
      result = []

      Async do
        semaphore = Async::Semaphore.new(concurrency_limit)

        tasks = items.map do |item|
          semaphore.async do
            yield(item)
          end
        end

        result = tasks.map(&:wait)
      end.wait

      return result
    end

Spec:

require "rails_helper"

RSpec.describe AsyncUtils do
  describe ".async_map" do
    subject { described_class.async_map(items:, concurrency_limit:, &block) }

    context "when the block raises an error" do
      let(:block) { ->(_) { raise "test error" } }
      let(:items) { [1, 2, 3] }
      let(:concurrency_limit) { Float::INFINITY }

      it "propagates the error" do
        expect { subject }.to raise_error("test error")
      end
    end
  end
end

Test output:

    when the block raises an error
  0.0s     warn: Async::Task [oid=0x7b34] [ec=0x7b48] [pid=150195] [2025-04-09 11:52:45 +0000]
               | Task may have ended with unhandled exception.
               |   RuntimeError: test error
               |   → spec/services/async_utils_spec.rb:40 in `block (5 levels) in <top (required)>'
               |     app/services/async_utils.rb:20 in `block (3 levels) in async_map'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/semaphore.rb:68 in `block in async'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:200 in `block in run'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:438 in `block in schedule'
  0.0s     warn: Async::Task [oid=0x7b5c] [ec=0x7b70] [pid=150195] [2025-04-09 11:52:45 +0000]
               | Task may have ended with unhandled exception.
               |   RuntimeError: test error
               |   → spec/services/async_utils_spec.rb:40 in `block (5 levels) in <top (required)>'
               |     app/services/async_utils.rb:20 in `block (3 levels) in async_map'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/semaphore.rb:68 in `block in async'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:200 in `block in run'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:438 in `block in schedule'
  0.0s     warn: Async::Task [oid=0x7b84] [ec=0x7b98] [pid=150195] [2025-04-09 11:52:45 +0000]
               | Task may have ended with unhandled exception.
               |   RuntimeError: test error
               |   → spec/services/async_utils_spec.rb:40 in `block (5 levels) in <top (required)>'
               |     app/services/async_utils.rb:20 in `block (3 levels) in async_map'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/semaphore.rb:68 in `block in async'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:200 in `block in run'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:438 in `block in schedule'
  0.0s     warn: Async::Task [oid=0x7bac] [ec=0x7bc0] [pid=150195] [2025-04-09 11:52:45 +0000]
               | Task may have ended with unhandled exception.
               |   RuntimeError: test error
               |   → spec/services/async_utils_spec.rb:40 in `block (5 levels) in <top (required)>'
               |     app/services/async_utils.rb:20 in `block (3 levels) in async_map'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/semaphore.rb:68 in `block in async'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:200 in `block in run'
               |     /api-bundle/ruby/3.3.0/gems/async-2.23.1/lib/async/task.rb:438 in `block in schedule'

So my question is: should I just disable these noisy logs, or do they necessarily point to actual problems in my code? Thanks.

[ioquatix]

You should check out this PR: socketry/async-await#10, basically add finished: false which indicates that while we aren't waiting yet, we will eventually wait.

finished: nil (the default) means unspecified and will log an exception because we don't know if it is going to be handled or not. Unfortunately Async cannot read the future.