Class: AtomicRuby::AtomicThreadPool

Inherits:
Object
  • Object
show all
Defined in:
lib/atomic-ruby/atomic_thread_pool.rb,
sig/generated/atomic-ruby/atomic_thread_pool.rbs

Overview

Note:

This class is NOT Ractor-safe as it contains mutable thread state that cannot be safely shared across ractors.

Provides a fixed-size thread pool using atomic operations for work queuing.

AtomicThreadPool maintains a fixed number of worker threads that process work items from an AtomicQueue. Both enqueueing and dequeueing are O(1) and lock-free, so concurrent producers and consumers never block one another.

Examples:

Basic usage

pool = AtomicThreadPool.new(size: 4)
pool << proc { puts "Hello from worker thread!" }
pool << proc { puts "Another work item" }
pool.shutdown

Processing work with results

results = []
pool = AtomicThreadPool.new(size: 2, name: "Calculator")

10.times do |index|
  pool << proc { results << index * 2 }
end

pool.shutdown
puts results.sort #=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

Monitoring pool state

pool = AtomicThreadPool.new(size: 3)
puts pool.length        #=> 3
puts pool.queue_length  #=> 0
puts pool.active_count  #=> 0

5.times { pool << proc { sleep(1) } }
puts pool.queue_length  #=> 2 (3 workers busy, 2 queued)
puts pool.active_count  #=> 3 (3 workers processing)

Defined Under Namespace

Classes: EnqueuedWorkAfterShutdownError, Error

Instance Method Summary collapse

Constructor Details

#initialize(size:, name: nil, on_error: nil) ⇒ AtomicThreadPool

Creates a new thread pool with the specified size.

Examples:

Create a basic pool

pool = AtomicThreadPool.new(size: 4)

Create a named pool

pool = AtomicThreadPool.new(size: 2, name: "Database Workers")

Create a pool with a custom error handler

errors = []
pool = AtomicThreadPool.new(size: 2, on_error: ->(err) { errors << err })

Parameters:

  • size (Integer) —

    The number of worker threads to create (must be positive)

  • name (String, nil) (defaults to: nil) —

    Optional name for the thread pool (used in thread names)

  • on_error (Proc, nil) (defaults to: nil) —

    Optional error handler called with the exception when a work item raises. Receives the exception as its argument. When nil, errors are printed to stderr

  • size: (Integer)
  • name: (String, nil) (defaults to: nil)
  • on_error: (Proc, nil) (defaults to: nil)

Raises:

  • (ArgumentError) —

    if size is not a positive integer

  • (ArgumentError) —

    if name is provided but not a string

  • (ArgumentError) —

    if on_error is provided but not a Proc



78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 78

def initialize(size:, name: nil, on_error: nil)
  raise ArgumentError, "size must be a positive Integer" unless size.is_a?(Integer) && size > 0
  raise ArgumentError, "name must be a String" unless name.nil? || name.is_a?(String)
  raise ArgumentError, "on_error must be a Proc" unless on_error.nil? || on_error.is_a?(Proc)

  @size = size
  @name = name
  @on_error = on_error

  @queue = AtomicQueue.new
  @shutdown = AtomicBoolean.new(false)
  @work_available = AtomicConditionVariable.new
  @started_thread_count = Atom.new(0)
  @active_thread_count = Atom.new(0)
  @threads = []

  start
end

Instance Method Details

#<<(work) ⇒ void

This method returns an undefined value.

Enqueues work to be executed by the thread pool.

The work item must respond to #call (typically a Proc or lambda). Work items are executed in FIFO order by available worker threads. If all workers are busy, the work is queued atomically. Enqueueing is O(1) regardless of current queue depth.

Examples:

Enqueue a simple task

pool << proc { puts "Hello World" }

Enqueue a lambda with parameters

calculator = ->(a, b) { puts a + b }
pool << proc { calculator.call(2, 3) }

Enqueue work that captures variables

name = "Alice"
pool << proc { puts "Processing #{name}" }

Parameters:

  • work (#call) —

    A callable object to be executed by a worker thread

Raises:



120
121
122
123
124
125
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 120

def <<(work)
  raise EnqueuedWorkAfterShutdownError if @shutdown.true?

  @queue.push(work)
  @work_available.signal
end

#active_count ⇒ Integer

Returns the number of worker threads currently executing work.

This represents threads that have picked up a work item and are actively processing it. The count includes threads in the middle of executing work.call, but excludes threads that are idle or waiting for work.

Examples:

Monitor active workers

pool = AtomicThreadPool.new(size: 4)
puts pool.active_count #=> 0

5.times { pool << proc { sleep(1) } }
sleep(0.1) # Give threads time to pick up work
puts pool.active_count #=> 4 (all workers busy)
puts pool.queue_length #=> 1 (one item still queued)

Calculate total load

total_load = pool.active_count + pool.queue_length
puts "Total pending work: #{total_load}"

Returns:

  • (Integer) —

    The number of threads actively processing work



195
196
197
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 195

def active_count
  @active_thread_count.value
end

#length ⇒ Integer Also known as: size

Returns the number of currently alive worker threads.

This count decreases as the pool shuts down and threads terminate. During normal operation, this should equal the size parameter passed to the constructor.

Examples:

pool = AtomicThreadPool.new(size: 4)
puts pool.length #=> 4
pool.shutdown
puts pool.length #=> 0

Returns:

  • (Integer) —

    The number of alive worker threads



142
143
144
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 142

def length
  @threads.select(&:alive?).length
end

#queue_length ⇒ Integer Also known as: queue_size

Returns the number of work items currently queued for execution.

This represents work that has been enqueued but not yet picked up by a worker thread. A high queue length indicates that work is being submitted faster than it can be processed.

Examples:

pool = AtomicThreadPool.new(size: 2)
5.times { pool << proc { sleep(1) } }
puts pool.queue_length #=> 3 (2 workers busy, 3 queued)

Returns:

  • (Integer) —

    The number of queued work items



164
165
166
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 164

def queue_length
  @queue.size
end

#shutdown ⇒ void

This method returns an undefined value.

Gracefully shuts down the thread pool.

This method:

  1. Marks the pool as shutdown (preventing new work from being enqueued)
  2. Waits for all currently queued work to complete
  3. Waits for all worker threads to terminate

After shutdown, all worker threads will be terminated and the pool cannot be restarted. Attempting to enqueue work after shutdown will raise an exception.

Examples:

pool = AtomicThreadPool.new(size: 4)
10.times { |index| pool << proc { puts index } }
pool.shutdown # waits for all work to complete
puts pool.length #=> 0

Raises:



221
222
223
224
225
226
227
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 221

def shutdown
  return if @shutdown.true?

  @shutdown.make_true
  @work_available.broadcast
  @threads.each(&:join)
end

#start ⇒ void

This method returns an undefined value.

Starts the worker threads for the thread pool.

This method is called automatically during initialization. It creates the specified number of worker threads and waits for all threads to be fully started before returning.



240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
 
# File 'lib/atomic-ruby/atomic_thread_pool.rb', line 240

def start
  @size.times do |num|
    @threads << Thread.new(num) do |idx|
      thread_name = String.new("AtomicThreadPool thread #{idx}")
      thread_name << " for #{@name}" if @name
      Thread.current.name = thread_name

      @started_thread_count.swap { |current_count| current_count + 1 }

      loop do
        work = nil
        should_shutdown = false

        @work_available.wait do
          work = @queue.pop
          should_shutdown = @shutdown.true? && @queue.empty? unless work
          work || should_shutdown
        end

        break if should_shutdown

        @active_thread_count.swap { |current_count| current_count + 1 }
        begin
          work.call
        rescue => err
          if @on_error
            @on_error.call(err)
          else
            warn "#{thread_name} rescued:"
            warn err.full_message
          end
        ensure
          @active_thread_count.swap { |current_count| current_count - 1 }
        end
      end
    end
  end
  @threads.freeze

  Thread.pass until @started_thread_count.value == @size
end