class Concurrent::Delay
Lazy evaluation of a block yielding an immutable result. Useful for expensive operations that may never be needed. It may be non-blocking, supports the `Concern::Obligation` interface, and accepts the injection of custom executor upon which to execute the block. Processing of block will be deferred until the first time `#value` is called. At that time the caller can choose to return immediately and let the block execute asynchronously, block indefinitely, or block with a timeout.
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::Concern::Dereferenceable` mixin to support thread safety of the reference returned by `#value`.
@!macro copy_options
@!macro delay_note_regarding_blocking
@note The default behavior of `Delay` is to block indefinitely when calling either `value` or `wait`, executing the delayed operation on the current thread. This makes the `timeout` value completely irrelevant. To enable non-blocking behavior, use the `executor` constructor option. This will cause the delayed operation to be execute on the given executor, allowing the call to timeout.
Public Class Methods
Create a new `Delay` in the `:pending` state.
@!macro executor_and_deref_options
@yield the delayed operation to perform
@raise [ArgumentError] if no block is given
# File lib/concurrent-ruby/concurrent/delay.rb, line 62 def initialize(opts = {}, &block) raise ArgumentError.new('no block given') unless block_given? super(&nil) synchronize { ns_initialize(opts, &block) } end
Public Instance Methods
Reconfigures the block returning the value if still `#incomplete?`
@yield the delayed operation to perform @return [true, false] if success
# File lib/concurrent-ruby/concurrent/delay.rb, line 146 def reconfigure(&block) synchronize do raise ArgumentError.new('no block given') unless block_given? unless @evaluation_started @task = block true else false end end end
Return the value this object represents after applying the options specified by the `#set_deref_options` method. If the delayed operation raised an exception this method will return nil. The execption object can be accessed via the `#reason` method.
@param [Numeric] timeout the maximum number of seconds to wait @return [Object] the current value of the object
@!macro delay_note_regarding_blocking
Concurrent::Concern::Obligation#value
# File lib/concurrent-ruby/concurrent/delay.rb, line 77 def value(timeout = nil) if @executor # TODO (pitr 12-Sep-2015): broken unsafe read? super else # this function has been optimized for performance and # should not be modified without running new benchmarks synchronize do execute = @evaluation_started = true unless @evaluation_started if execute begin set_state(true, @task.call, nil) rescue => ex set_state(false, nil, ex) end elsif incomplete? raise IllegalOperationError, 'Recursive call to #value during evaluation of the Delay' end end if @do_nothing_on_deref @value else apply_deref_options(@value) end end end
Return the value this object represents after applying the options specified by the `#set_deref_options` method. If the delayed operation raised an exception, this method will raise that exception (even when) the operation has already been executed).
@param [Numeric] timeout the maximum number of seconds to wait @return [Object] the current value of the object @raise [Exception] when `#rejected?` raises `#reason`
@!macro delay_note_regarding_blocking
Concurrent::Concern::Obligation#value!
# File lib/concurrent-ruby/concurrent/delay.rb, line 113 def value!(timeout = nil) if @executor super else result = value raise @reason if @reason result end end
Return the value this object represents after applying the options specified by the `#set_deref_options` method.
@param [Integer] timeout (nil) the maximum number of seconds to wait for
the value to be computed. When `nil` the caller will block indefinitely.
@return [Object] self
@!macro delay_note_regarding_blocking
Concurrent::Concern::Obligation#wait
# File lib/concurrent-ruby/concurrent/delay.rb, line 132 def wait(timeout = nil) if @executor execute_task_once super(timeout) else value end self end
Protected Instance Methods
# File lib/concurrent-ruby/concurrent/delay.rb, line 160 def ns_initialize(opts, &block) init_obligation set_deref_options(opts) @executor = opts[:executor] @task = block @state = :pending @evaluation_started = false end