Add bin and edit workflow

bin/gems/concurrent-ruby-1.3.5/lib/concurrent-ruby/concurrent/ivar.rb

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+require 'concurrent/constants'
+require 'concurrent/errors'
+require 'concurrent/collection/copy_on_write_observer_set'
+require 'concurrent/concern/obligation'
+require 'concurrent/concern/observable'
+require 'concurrent/executor/safe_task_executor'
+require 'concurrent/synchronization/lockable_object'
+
+module Concurrent
+
+  # 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.
+  #
+  # ## Examples
+  #
+  # Create, set and get an `IVar`
+  #
+  # ```ruby
+  # ivar = Concurrent::IVar.new
+  # ivar.set 14
+  # ivar.value #=> 14
+  # ivar.set 2 # would now be an error
+  # ```
+  #
+  # ## See Also
+  #
+  # 1. For the theory: Arvind, R. Nikhil, and K. Pingali.
+  #    [I-Structures: Data structures for parallel computing](http://dl.acm.org/citation.cfm?id=69562).
+  #    In Proceedings of Workshop on Graph Reduction, 1986.
+  # 2. For recent application:
+  #    [DataDrivenFuture in Habanero Java from Rice](http://www.cs.rice.edu/~vs3/hjlib/doc/edu/rice/hj/api/HjDataDrivenFuture.html).
+  class IVar < Synchronization::LockableObject
+    include Concern::Obligation
+    include Concern::Observable
+
+    # Create a new `IVar` in the `:pending` state with the (optional) initial value.
+    #
+    # @param [Object] value the initial value
+    # @param [Hash] opts the options to create a message with
+    # @option opts [String] :dup_on_deref (false) call `#dup` before returning
+    #   the data
+    # @option opts [String] :freeze_on_deref (false) call `#freeze` before
+    #   returning the data
+    # @option opts [String] :copy_on_deref (nil) call the given `Proc` passing
+    #   the internal value and returning the value returned from the proc
+    def initialize(value = NULL, opts = {}, &block)
+      if value != NULL && block_given?
+        raise ArgumentError.new('provide only a value or a block')
+      end
+      super(&nil)
+      synchronize { ns_initialize(value, opts, &block) }
+    end
+
+    # Add an observer on this object that will receive notification on update.
+    #
+    # Upon completion the `IVar` will notify all observers in a thread-safe 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).
+    #
+    # @param [Object] observer the object that will be notified of changes
+    # @param [Symbol] func symbol naming the method to call when this
+    #   `Observable` has changes`
+    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
+
+      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
+
+    # @!macro ivar_set_method
+    #   Set the `IVar` to a value and wake or notify all threads waiting on it.
+    #
+    #   @!macro ivar_set_parameters_and_exceptions
+    #     @param [Object] value the value to store in the `IVar`
+    #     @yield A block operation to use for setting the value
+    #     @raise [ArgumentError] if both a value and a block are given
+    #     @raise [Concurrent::MultipleAssignmentError] if the `IVar` has already
+    #       been set or otherwise completed
+    #
+    #   @return [IVar] self
+    def set(value = NULL)
+      check_for_block_or_value!(block_given?, value)
+      raise MultipleAssignmentError unless compare_and_set_state(:processing, :pending)
+
+      begin
+        value = yield if block_given?
+        complete_without_notification(true, value, nil)
+      rescue => ex
+        complete_without_notification(false, nil, ex)
+      end
+
+      notify_observers(self.value, reason)
+      self
+    end
+
+    # @!macro ivar_fail_method
+    #   Set the `IVar` to failed due to some error and wake or notify all threads waiting on it.
+    #
+    #   @param [Object] reason for the failure
+    #   @raise [Concurrent::MultipleAssignmentError] if the `IVar` has already
+    #     been set or otherwise completed
+    #   @return [IVar] self
+    def fail(reason = StandardError.new)
+      complete(false, nil, reason)
+    end
+
+    # Attempt to set the `IVar` with the given value or block. Return a
+    # boolean indicating the success or failure of the set operation.
+    #
+    # @!macro ivar_set_parameters_and_exceptions
+    #
+    # @return [Boolean] true if the value was set else false
+    def try_set(value = NULL, &block)
+      set(value, &block)
+      true
+    rescue MultipleAssignmentError
+      false
+    end
+
+    protected
+
+    # @!visibility private
+    def ns_initialize(value, opts)
+      value = yield if block_given?
+      init_obligation
+      self.observers = Collection::CopyOnWriteObserverSet.new
+      set_deref_options(opts)
+
+      @state = :pending
+      if value != NULL
+        ns_complete_without_notification(true, value, nil)
+      end
+    end
+
+    # @!visibility private
+    def safe_execute(task, args = [])
+      if compare_and_set_state(:processing, :pending)
+        success, val, reason = SafeTaskExecutor.new(task, rescue_exception: true).execute(*@args)
+        complete(success, val, reason)
+        yield(success, val, reason) if block_given?
+      end
+    end
+
+    # @!visibility private
+    def complete(success, value, reason)
+      complete_without_notification(success, value, reason)
+      notify_observers(self.value, reason)
+      self
+    end
+
+    # @!visibility private
+    def complete_without_notification(success, value, reason)
+      synchronize { ns_complete_without_notification(success, value, reason) }
+      self
+    end
+
+    # @!visibility private
+    def notify_observers(value, reason)
+      observers.notify_and_delete_observers{ [Time.now, value, reason] }
+    end
+
+    # @!visibility private
+    def ns_complete_without_notification(success, value, reason)
+      raise MultipleAssignmentError if [:fulfilled, :rejected].include? @state
+      set_state(success, value, reason)
+      event.set
+    end
+
+    # @!visibility private
+    def check_for_block_or_value!(block_given, value) # :nodoc:
+      if (block_given && value != NULL) || (! block_given && value == NULL)
+        raise ArgumentError.new('must set with either a value or a block')
+      end
+    end
+  end
+end