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require 'concurrent/utility/engine'
require 'concurrent/executor/thread_pool_executor'
module Concurrent
# @!macro [new] thread_pool_executor_constant_default_max_pool_size
# Default maximum number of threads that will be created in the pool.
# @!macro [new] thread_pool_executor_constant_default_min_pool_size
# Default minimum number of threads that will be retained in the pool.
# @!macro [new] thread_pool_executor_constant_default_max_queue_size
# Default maximum number of tasks that may be added to the task queue.
# @!macro [new] thread_pool_executor_constant_default_thread_timeout
# Default maximum number of seconds a thread in the pool may remain idle
# before being reclaimed.
# @!macro [new] thread_pool_executor_attr_reader_max_length
# The maximum number of threads that may be created in the pool.
# @return [Integer] The maximum number of threads that may be created in the pool.
# @!macro [new] thread_pool_executor_attr_reader_min_length
# The minimum number of threads that may be retained in the pool.
# @return [Integer] The minimum number of threads that may be retained in the pool.
# @!macro [new] thread_pool_executor_attr_reader_largest_length
# The largest number of threads that have been created in the pool since construction.
# @return [Integer] The largest number of threads that have been created in the pool since construction.
# @!macro [new] thread_pool_executor_attr_reader_scheduled_task_count
# The number of tasks that have been scheduled for execution on the pool since construction.
# @return [Integer] The number of tasks that have been scheduled for execution on the pool since construction.
# @!macro [new] thread_pool_executor_attr_reader_completed_task_count
# 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 [new] 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.
# @!macro [new] thread_pool_executor_attr_reader_max_queue
# The maximum number of tasks that may be waiting in the work queue at any one time.
# When the queue size reaches `max_queue` subsequent tasks will be rejected in
# accordance with the configured `fallback_policy`.
#
# @return [Integer] The maximum number of tasks that may be waiting in the work queue at any one time.
# When the queue size reaches `max_queue` subsequent tasks will be rejected in
# accordance with the configured `fallback_policy`.
# @!macro [new] thread_pool_executor_attr_reader_length
# The number of threads currently in the pool.
# @return [Integer] The number of threads currently in the pool.
# @!macro [new] thread_pool_executor_attr_reader_queue_length
# The number of tasks in the queue awaiting execution.
# @return [Integer] The number of tasks in the queue awaiting execution.
# @!macro [new] thread_pool_executor_attr_reader_remaining_capacity
# Number of tasks that may be enqueued before reaching `max_queue` and rejecting
# new tasks. A value of -1 indicates that the queue may grow without bound.
#
# @return [Integer] Number of tasks that may be enqueued before reaching `max_queue` and rejecting
# new tasks. A value of -1 indicates that the queue may grow without bound.
# @!macro [new] thread_pool_executor_public_api
#
# @!macro abstract_executor_service_public_api
#
# @!attribute [r] max_length
# @!macro thread_pool_executor_attr_reader_max_length
#
# @!attribute [r] min_length
# @!macro thread_pool_executor_attr_reader_min_length
#
# @!attribute [r] largest_length
# @!macro thread_pool_executor_attr_reader_largest_length
#
# @!attribute [r] scheduled_task_count
# @!macro thread_pool_executor_attr_reader_scheduled_task_count
#
# @!attribute [r] completed_task_count
# @!macro thread_pool_executor_attr_reader_completed_task_count
#
# @!attribute [r] idletime
# @!macro thread_pool_executor_attr_reader_idletime
#
# @!attribute [r] max_queue
# @!macro thread_pool_executor_attr_reader_max_queue
#
# @!attribute [r] length
# @!macro thread_pool_executor_attr_reader_length
#
# @!attribute [r] queue_length
# @!macro thread_pool_executor_attr_reader_queue_length
#
# @!attribute [r] remaining_capacity
# @!macro thread_pool_executor_attr_reader_remaining_capacity
#
# @!method can_overflow?
# @!macro executor_service_method_can_overflow_question
# @!macro [new] thread_pool_options
#
# **Thread Pool Options**
#
# Thread pools support several configuration options:
#
# * `idletime`: The number of seconds that a thread may be idle before being reclaimed.
# * `max_queue`: The maximum number of tasks that may be waiting in the work queue at
# any one time. When the queue size reaches `max_queue` subsequent tasks will be
# rejected in accordance with the configured `fallback_policy`.
# * `auto_terminate`: When true (default) an `at_exit` handler will be registered which
# will stop the thread pool when the application exits. See below for more information
# on shutting down thread pools.
# * `fallback_policy`: The policy defining how rejected tasks are handled.
#
# Three fallback policies are supported:
#
# * `:abort`: Raise a `RejectedExecutionError` exception and discard the task.
# * `:discard`: Discard the task and return false.
# * `:caller_runs`: Execute the task on the calling thread.
#
# **Shutting Down Thread Pools**
#
# Killing a thread pool while tasks are still being processed, either by calling
# the `#kill` method or at application exit, will have unpredictable results. There
# is no way for the thread pool to know what resources are being used by the
# in-progress tasks. When those tasks are killed the impact on those resources
# cannot be predicted. The *best* practice is to explicitly shutdown all thread
# pools using the provided methods:
#
# * Call `#shutdown` to initiate an orderly termination of all in-progress tasks
# * Call `#wait_for_termination` with an appropriate timeout interval an allow
# the orderly shutdown to complete
# * Call `#kill` *only when* the thread pool fails to shutdown in the allotted time
#
# On some runtime platforms (most notably the JVM) the application will not
# exit until all thread pools have been shutdown. To prevent applications from
# "hanging" on exit all thread pools include an `at_exit` handler that will
# stop the thread pool when the application exists. This handler uses a brute
# force method to stop the pool and makes no guarantees regarding resources being
# used by any tasks still running. Registration of this `at_exit` handler can be
# prevented by setting the thread pool's constructor `:auto_terminate` option to
# `false` when the thread pool is created. All thread pools support this option.
#
# ```ruby
# pool1 = Concurrent::FixedThreadPool.new(5) # an `at_exit` handler will be registered
# pool2 = Concurrent::FixedThreadPool.new(5, auto_terminate: false) # prevent `at_exit` handler registration
# ```
#
# @note Failure to properly shutdown a thread pool can lead to unpredictable results.
# Please read *Shutting Down Thread Pools* for more information.
#
# @see http://docs.oracle.com/javase/tutorial/essential/concurrency/pools.html Java Tutorials: Thread Pools
# @see http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html Java Executors class
# @see http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html Java ExecutorService interface
# @see http://ruby-doc.org//core-2.2.0/Kernel.html#method-i-at_exit Kernel#at_exit
# @!macro [attach] fixed_thread_pool
#
# A thread pool with a set number of threads. The number of threads in the pool
# is set on construction and remains constant. When all threads are busy new
# tasks `#post` to the thread pool are enqueued until a thread becomes available.
# Should a thread crash for any reason the thread will immediately be removed
# from the pool and replaced.
#
# The API and behavior of this class are based on Java's `FixedThreadPool`
#
# @!macro thread_pool_options
class FixedThreadPool < ThreadPoolExecutor
# @!macro [attach] fixed_thread_pool_method_initialize
#
# Create a new thread pool.
#
# @param [Integer] num_threads the number of threads to allocate
# @param [Hash] opts the options defining pool behavior.
# @option opts [Symbol] :fallback_policy (`:abort`) the fallback policy
#
# @raise [ArgumentError] if `num_threads` is less than or equal to zero
# @raise [ArgumentError] if `fallback_policy` is not a known policy
#
# @see http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool-int-
def initialize(num_threads, opts = {})
raise ArgumentError.new('number of threads must be greater than zero') if num_threads.to_i < 1
defaults = { max_queue: DEFAULT_MAX_QUEUE_SIZE,
idletime: DEFAULT_THREAD_IDLETIMEOUT }
overrides = { min_threads: num_threads,
max_threads: num_threads }
super(defaults.merge(opts).merge(overrides))
end
end
end
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