Ruby thread concurrency limit demo

thread_concurrency_limit_demo.rb

# The total number of threads we want to all to run at the same time
concurrent_thread_limit = 4
# The total number of threads to run for this demo
total_thread_count = 13

@threads = []

##
# Print the status of all threads to the console
#
def print_threads_status(current = nil)
  msg = Time.now.strftime('%H:%M:%S - ')

  @threads.each_with_index do |t, i|
    # A status of false indicates successfuly thread completion
    # https://ruby-doc.org/core-2.6.5/Thread.html#method-i-status
    status = (t.status || 'done')
    msg << "#{i}: #{status}#{i == current ? '*' : ' '} ".ljust(10)
  end

  puts msg
end
# This will block until all threads have been created
total_thread_count.times do |i|
  # Wait until there are fewer running threads then our limit
  while @threads.count(&:alive?) >= concurrent_thread_limit
    sleep 0.01
  end

  # Create a new thread that starts running right away
  @threads << Thread.new do
    print_threads_status(i)
    sleep 1 + rand
  end
end

# Make sure all threads have completed by joining them to the main thread.
@threads.each(&:join)

puts "\nThreads are all joined now."

print_threads_status

puts "\nDone!"