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Class: Concurrent::FixedThreadPool

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ThreadPoolExecutor
Instance Chain:
self, ThreadPoolExecutor
Inherits: Concurrent::ThreadPoolExecutor
Defined in: lib/concurrent-ruby/concurrent/executor/fixed_thread_pool.rb

Overview

Note:

Failure to properly shutdown a thread pool can lead to unpredictable results. Please read *Shutting Down Thread Pools* for more information.

A thread pool that reuses a fixed number of threads operating off an unbounded queue. At any point, at most num_threads will be active processing tasks. 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 **Thread Pool Options**

Thread pools support several configuration options:

  • idletime: The number of seconds that a thread may be idle before being reclaimed.

  • name: The name of the executor (optional). Printed in the executor’s #to_s output and a -worker- name is given to its threads if supported by used Ruby implementation. is uniq for each thread.

  • 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 and no new threads can be created, subsequent tasks will be rejected in accordance with the configured fallback_policy.

  • auto_terminate: When true (default), the threads started will be marked as daemon.

  • 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 threads can be marked as daemon according to the :auto_terminate option.

“‘ruby pool1 = FixedThreadPool.new(5) # threads will be marked as daemon pool2 = FixedThreadPool.new(5, auto_terminate: false) # mark threads as non-daemon “`

See Also:

Class Method Summary

Instance Attribute Summary

ThreadPoolExecutor - Inherited

#completed_task_count

The number of tasks that have been completed by the pool since construction.
#fallback_policy,
#idletime

The number of seconds that a thread may be idle before being reclaimed.
#largest_length

The largest number of threads that have been created in the pool since construction.
#length

The number of threads currently in the pool.
#max_length

The maximum number of threads that may be created in the pool.
#max_queue

The maximum number of tasks that may be waiting in the work queue at any one time.
#min_length

The minimum number of threads that may be retained in the pool.
#queue_length

The number of tasks in the queue awaiting execution.
#remaining_capacity

Number of tasks that may be enqueued before reaching max_queue and rejecting new tasks.
#scheduled_task_count

The number of tasks that have been scheduled for execution on the pool since construction.

Instance Method Summary

ThreadPoolExecutor - Inherited

#<<

Submit a task to the executor for asynchronous processing.
#auto_terminate=

Set the auto-terminate behavior for this executor.
#auto_terminate?

Is the executor auto-terminate when the application exits?
#can_overflow?

Does the task queue have a maximum size?
#kill

Begin an immediate shutdown.
#post

Submit a task to the executor for asynchronous processing.
#prune_pool

Prune the thread pool of unneeded threads.
#running?

Is the executor running?
#serialized?

Does this executor guarantee serialization of its operations?
#shutdown

Begin an orderly shutdown.
#shutdown?

Is the executor shutdown?
#shuttingdown?

Is the executor shuttingdown?
#wait_for_termination

Block until executor shutdown is complete or until timeout seconds have passed.

Constructor Details

.new(num_threads, opts = {}) ⇒ FixedThreadPool

Raises:

  • (ArgumentError)
[ GitHub ] 

  


# File 'lib/concurrent-ruby/concurrent/executor/fixed_thread_pool.rb', line 215



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