Create method ThreadPoolExecutor#available_worker_count to expose num…

…ber of idle/uncreated worker threads

lib/concurrent-ruby/concurrent/executor/fixed_thread_pool.rb

@@ -39,6 +39,10 @@ module Concurrent
  # The number of tasks that have been completed by the pool since construction.
  # @return [Integer] The number of tasks that have been completed by the pool since construction.
 
+ # @!macro thread_pool_executor_attr_reader_available_worker_count
+ # The number of worker threads that are available to process tasks (either idle or uncreated)
+ # @return [Integer] The number of worker threads that are available to process tasks (either idle or uncreated)
+
  # @!macro thread_pool_executor_attr_reader_idletime
  # The number of seconds that a thread may be idle before being reclaimed.
  # @return [Integer] The number of seconds that a thread may be idle before being reclaimed.

lib/concurrent-ruby/concurrent/executor/java_thread_pool_executor.rb

@@ -73,6 +73,11 @@ def completed_task_count
  @executor.getCompletedTaskCount
  end
 
+ # @!macro thread_pool_executor_attr_reader_available_worker_count
+ def available_worker_count
+ @executor.getMaximumPoolSize - @executor.getActiveCount
+ end
+
  # @!macro thread_pool_executor_attr_reader_idletime
  def idletime
  @executor.getKeepAliveTime(java.util.concurrent.TimeUnit::SECONDS)

lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb

@@ -61,6 +61,15 @@ def completed_task_count
  synchronize { @completed_task_count }
  end
 
+ # @!macro thread_pool_executor_attr_reader_available_worker_count
+ def available_worker_count
+ synchronize do
+ uncreated_workers = @max_length - @pool.length
+ idle_workers = @ready.length
+ uncreated_workers + idle_workers
+ end
+ end
+
  # @!macro executor_service_method_can_overflow_question
  def can_overflow?
  synchronize { ns_limited_queue? }

spec/concurrent/executor/thread_pool_executor_shared.rb

@@ -258,6 +258,27 @@
  end
  end
 
+ context '#available_worker_count' do
+ subject do
+ described_class.new(
+ min_threads: 5,
+ max_threads: 10,
+ idletime: 60,
+ max_queue: 0,
+ fallback_policy: :discard
+ )
+ end
+
+ it 'returns the number of available (ready/idle or uncreated) workers' do
+ expect(subject.available_worker_count).to eq 10
+ latch = Concurrent::CountDownLatch.new(7)
+ 7.times{ subject.post{ sleep 0.1; latch.count_down } }
+ expect(subject.available_worker_count).to eq 3
+ expect(latch.wait(1)).to be_truthy
+ expect(subject.available_worker_count).to eq 10
+ end
+ end
+
  context '#fallback_policy' do
 
  let!(:min_threads){ 1 }