Class: Concurrent::IVar

Inherits:
Object
  • Object
show all
Includes:
Obligation, Observable
Defined in:
lib/concurrent/ivar.rb

Overview

An IVar is like a future that you can assign. As a future is a value that is being computed that you can wait on, an IVar is a value that is waiting to be assigned, that you can wait on. IVars are single assignment and deterministic.

Then, express futures as an asynchronous computation that assigns an IVar. The IVar becomes the primitive on which [futures](Future) and [dataflow](Dataflow) are built.

An IVar is a single-element container that is normally created empty, and can only be set once. The I in IVar stands for immutable. Reading an IVar normally blocks until it is set. It is safe to set and read an IVar from different threads.

If you want to have some parallel task set the value in an IVar, you want a Future. If you want to create a graph of parallel tasks all executed when the values they depend on are ready you want dataflow. IVar is generally a low-level primitive.

**See Also:**

Examples:

Create, set and get an IVar

ivar = Concurrent::IVar.new
ivar.set 14
ivar.get #=> 14
ivar.set 2 # would now be an error

Direct Known Subclasses

Channel::Probe, Future, ScheduledTask

Instance Method Summary collapse

Methods included from Observable

#count_observers, #delete_observer, #delete_observers, #with_observer

Methods included from Obligation

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

Methods included from Dereferenceable

#value

Constructor Details

#initialize(value = NO_VALUE, opts = {}) ⇒ IVar

Create a new IVar in the :pending state with the (optional) initial value.

Parameters:

  • (defaults to: NO_VALUE)

    the initial value

  • (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



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# File 'lib/concurrent/ivar.rb', line 49

def initialize(value = NO_VALUE, opts = {})
  init_obligation
  self.observers = CopyOnWriteObserverSet.new
  set_deref_options(opts)

  if value == NO_VALUE
    @state = :pending
  else
    set(value)
  end
end

Instance Method Details

#add_observer(observer = nil, func = :update, &block) ⇒ Object

Add an observer on this object that will receive notification on update.

Upon completion the IVar will notify all observers in a thread-say way. The func method of the observer will be called with three arguments: the Time at which the Future completed the asynchronous operation, the final value (or nil on rejection), and the final reason (or nil on fulfillment).

Parameters:

  • (defaults to: nil)

    the object that will be notified of changes

  • (defaults to: :update)

    symbol naming the method to call when this Observable has changes`

Raises:



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# File 'lib/concurrent/ivar.rb', line 70

def add_observer(observer = nil, func = :update, &block)
  raise ArgumentError.new('cannot provide both an observer and a block') if observer && block
  direct_notification = false

  if block
    observer = block
    func = :call
  end

  mutex.synchronize do
    if event.set?
      direct_notification = true
    else
      observers.add_observer(observer, func)
    end
  end

  observer.send(func, Time.now, self.value, reason) if direct_notification
  observer
end

#fail(reason = StandardError.new) ⇒ Object

Set the IVar to failed due to some error and wake or notify all threads waiting on it.

Parameters:

  • (defaults to: StandardError.new)

    for the failure

Raises:

  • if the IVar has already been set or otherwise completed



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# File 'lib/concurrent/ivar.rb', line 103

def fail(reason = StandardError.new)
  complete(false, nil, reason)
end

#set(value) ⇒ Object

Set the IVar to a value and wake or notify all threads waiting on it.

Parameters:

  • the value to store in the IVar

Raises:

  • if the IVar has already been set or otherwise completed



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# File 'lib/concurrent/ivar.rb', line 95

def set(value)
  complete(true, value, nil)
end