Thread without join (ARCH6041)

Key ruby.async.thread-without-join · Severity warning · Category async

A thread started without a matching join lets the spawning scope exit before the thread finishes. Its work may be cut short and exceptions raised inside it are silently lost.

Incorrect

def process_batch(items)
  items.each do |item|
    Thread.new { upload(item) }
  end
  # method returns; uploads may not finish, errors lost
end

Correct

def process_batch(items)
  threads = items.map do |item|
    Thread.new { upload(item) }
  end
  threads.each(&:join)
end

Fix

Keep each spawned thread in a variable and call join on it before leaving the scope.