Class: Concurrent::Delay

Inherits:
Object
  • Object
show all
Includes:
Obligation
Defined in:
lib/concurrent/delay.rb

Overview

Lazy evaluation of a block yielding an immutable result. Useful for expensive operations that may never be needed.

A ‘Delay` is similar to `Future` but solves a different problem. Where a `Future` schedules an operation for immediate execution and performs the operation asynchronously, a `Delay` (as the name implies) delays execution of the operation until the result is actually needed.

When a ‘Delay` is created its state is set to `pending`. The value and reason are both `nil`. The first time the `#value` method is called the enclosed opration will be run and the calling thread will block. Other threads attempting to call `#value` will block as well. Once the operation is complete the value will be set to the result of the operation or the reason will be set to the raised exception, as appropriate. All threads blocked on `#value` will return. Subsequent calls to `#value` will immediately return the cached value. The operation will only be run once. This means that any side effects created by the operation will only happen once as well.

‘Delay` includes the `Concurrent::Dereferenceable` mixin to support thread safety of the reference returned by `#value`.

See Also:

Since:

  • 0.6.0

Instance Method Summary collapse

Methods included from Obligation

#completed?, #exception, #fulfilled?, #incomplete?, #no_error!, #pending?, #reason, #rejected?, #state, #unscheduled?, #value, #value!

Methods included from Dereferenceable

#value

Constructor Details

#initialize(opts = {}) { ... } ⇒ Delay

Create a new ‘Delay` in the `:pending` state.

Parameters:

  • opts (Hash) (defaults to: {}) —

    the options to create a message with

Options Hash (opts):

  • :dup_on_deref (String) — default: false —

    call ‘#dup` before returning the data

  • :freeze_on_deref (String) — default: false —

    call ‘#freeze` before returning the data

  • :copy_on_deref (String) — default: nil —

    call the given ‘Proc` passing the internal value and returning the value returned from the proc

Yields:

  • the delayed operation to perform

Raises:

  • (ArgumentError) —

    if no block is given

Since:

  • 0.6.0



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# File 'lib/concurrent/delay.rb', line 48

def initialize(opts = {}, &block)
  raise ArgumentError.new('no block given') unless block_given?

  init_obligation
  @state = :pending
  @task  = block
  set_deref_options(opts)
  @task_executor = OptionsParser.get_task_executor_from(opts)
  @computing     = false
end

Instance Method Details

#reconfigure { ... } ⇒ true, false

reconfigures the block returning the value if still #incomplete?

Yields:

  • the delayed operation to perform

Returns:

  • (true, false) —

    if success

Since:

  • 0.6.0



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# File 'lib/concurrent/delay.rb', line 67

def reconfigure(&block)
  mutex.lock
  raise ArgumentError.new('no block given') unless block_given?
  unless @computing
    @task = block
    true
  else
    false
  end
ensure
  mutex.unlock
end

#wait(timeout) ⇒ Object

Since:

  • 0.6.0



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# File 'lib/concurrent/delay.rb', line 59

def wait(timeout)
  execute_task_once
  super timeout
end