Class: Concurrent::Promise
- Defined in:
- lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb
Overview
Promises are inspired by the JavaScript [Promises/A](wiki.commonjs.org/wiki/Promises/A) and [Promises/A+](promises-aplus.github.io/promises-spec/) specifications.
> A promise represents the eventual value returned from the single > completion of an operation.
Promises are similar to futures and share many of the same behaviours. Promises are far more robust, however. Promises can be chained in a tree structure where each promise may have zero or more children. Promises are chained using the ‘then` method. The result of a call to `then` is always another promise. Promises are resolved asynchronously (with respect to the main thread) but in a strict order: parents are guaranteed to be resolved before their children, children before their younger siblings. The `then` method takes two parameters: an optional block to be executed upon parent resolution and an optional callable to be executed upon parent failure. The result of each promise is passed to each of its children upon resolution. When a promise is rejected all its children will be summarily rejected and will receive the reason.
Promises have several possible states: :unscheduled, :pending, :processing, :rejected, or :fulfilled. These are also aggregated as ‘#incomplete?` and `#complete?`. When a Promise is created it is set to :unscheduled. Once the `#execute` method is called the state becomes :pending. Once a job is pulled from the thread pool’s queue and is given to a thread for processing (often immediately upon ‘#post`) the state becomes :processing. The future will remain in this state until processing is complete. A future that is in the :unscheduled, :pending, or :processing is considered `#incomplete?`. A `#complete?` Promise is either :rejected, indicating that an exception was thrown during processing, or :fulfilled, indicating success. If a Promise is :fulfilled its `#value` will be updated to reflect the result of the operation. If :rejected the `reason` will be updated with a reference to the thrown exception. The predicate methods `#unscheduled?`, `#pending?`, `#rejected?`, and `#fulfilled?` can be called at any time to obtain the state of the Promise, as can the `#state` method, which returns a symbol.
Retrieving the value of a promise is done through the ‘value` (alias: `deref`) method. Obtaining the value of a promise is a potentially blocking operation. When a promise is rejected a call to `value` will return `nil` immediately. When a promise is fulfilled a call to `value` will immediately return the current value. When a promise is pending a call to `value` will block until the promise is either rejected or fulfilled. A timeout value can be passed to `value` to limit how long the call will block. If `nil` the call will block indefinitely. If `0` the call will not block. Any other integer or float value will indicate the maximum number of seconds to block.
Promises run on the global thread pool.
## Copy Options
Object references in Ruby are mutable. This can lead to serious problems when the Concern::Obligation#value of an object is a mutable reference. Which is always the case unless the value is a ‘Fixnum`, `Symbol`, or similar “primitive” data type. Each instance can be configured with a few options that can help protect the program from potentially dangerous operations. Each of these options can be optionally set when the object instance is created:
-
‘:dup_on_deref` When true the object will call the `#dup` method on the `value` object every time the `#value` method is called (default: false)
-
‘:freeze_on_deref` When true the object will call the `#freeze` method on the `value` object every time the `#value` method is called (default: false)
-
‘:copy_on_deref` When given a `Proc` object the `Proc` will be run every time the `#value` method is called. The `Proc` will be given the current `value` as its only argument and the result returned by the block will be the return value of the `#value` call. When `nil` this option will be ignored (default: nil)
When multiple deref options are set the order of operations is strictly defined. The order of deref operations is:
-
‘:copy_on_deref`
-
‘:dup_on_deref`
-
‘:freeze_on_deref`
Because of this ordering there is no need to ‘#freeze` an object created by a provided `:copy_on_deref` block. Simply set `:freeze_on_deref` to `true`. Setting both `:dup_on_deref` to `true` and `:freeze_on_deref` to `true` is as close to the behavior of a “pure” functional language (like Erlang, Clojure, or Haskell) as we are likely to get in Ruby. ### Examples
Start by requiring promises
“‘ruby require ’concurrent’ “‘
Then create one
“‘ruby p = Concurrent::Promise.execute do
# do something
42
end
“‘
Promises can be chained using the ‘then` method. The `then` method accepts a block and an executor, to be executed on fulfillment, and a callable argument to be executed on rejection. The result of the each promise is passed as the block argument to chained promises.
“‘ruby p = Concurrent::Promise.new10.then{|x| x * 2}.then{|result| result - 10 }.execute “`
And so on, and so on, and so on…
“‘ruby p = Concurrent::Promise.fulfill(20).
then{|result| result - 10 }.
then{|result| result * 3 }.
then(executor: different_executor){|result| result % 5 }.execute
“‘
The initial state of a newly created Promise depends on the state of its parent:
-
if parent is unscheduled the child will be unscheduled
-
if parent is pending the child will be pending
-
if parent is fulfilled the child will be pending
-
if parent is rejected the child will be pending (but will ultimately be rejected)
Promises are executed asynchronously from the main thread. By the time a child Promise finishes intialization it may be in a different state than its parent (by the time a child is created its parent may have completed execution and changed state). Despite being asynchronous, however, the order of execution of Promise objects in a chain (or tree) is strictly defined.
There are multiple ways to create and execute a new ‘Promise`. Both ways provide identical behavior:
“‘ruby # create, operate, then execute p1 = Concurrent::Promise.new{ “Hello World!” } p1.state #=> :unscheduled p1.execute
# create and immediately execute p2 = Concurrent::Promise.new{ “Hello World!” }.execute
# execute during creation p3 = Concurrent::Promise.execute{ “Hello World!” } “‘
Once the ‘execute` method is called a `Promise` becomes `pending`:
“‘ruby p = Concurrent::Promise.execute{ “Hello, world!” } p.state #=> :pending p.pending? #=> true “`
Wait a little bit, and the promise will resolve and provide a value:
“‘ruby p = Concurrent::Promise.execute{ “Hello, world!” } sleep(0.1)
p.state #=> :fulfilled p.fulfilled? #=> true p.value #=> “Hello, world!” “‘
If an exception occurs, the promise will be rejected and will provide a reason for the rejection:
“‘ruby p = Concurrent::Promise.execute{ raise StandardError.new(“Here comes the Boom!”) } sleep(0.1)
p.state #=> :rejected p.rejected? #=> true p.reason #=> “#<StandardError: Here comes the Boom!>” “‘
#### Rejection
When a promise is rejected all its children will be rejected and will receive the rejection ‘reason` as the rejection callable parameter:
“‘ruby p = Concurrent::Promise.execute { Thread.pass; raise StandardError }
c1 = p.then(-> reason { 42 }) c2 = p.then(-> reason { raise ‘Boom!’ })
c1.wait.state #=> :fulfilled c1.value #=> 45 c2.wait.state #=> :rejected c2.reason #=> #<RuntimeError: Boom!> “‘
Once a promise is rejected it will continue to accept children that will receive immediately rejection (they will be executed asynchronously).
#### Aliases
The ‘then` method is the most generic alias: it accepts a block to be executed upon parent fulfillment and a callable to be executed upon parent rejection. At least one of them should be passed. The default block is `{ |result| result }` that fulfills the child with the parent value. The default callable is `{ |reason| raise reason }` that rejects the child with the parent reason.
-
‘on_success { |result| … }` is the same as `then {|result| … }`
-
‘rescue { |reason| … }` is the same as `then(Proc.new { |reason| … } )`
-
‘rescue` is aliased by `catch` and `on_error`
Class Method Summary collapse
-
.all?(*promises) ⇒ Boolean
Aggregates a collection of promises and executes the ‘then` condition if all aggregated promises succeed.
-
.any?(*promises) ⇒ Promise
Aggregates a collection of promises and executes the ‘then` condition if any aggregated promises succeed.
-
.execute(opts = {}, &block) ⇒ Promise
Create a new ‘Promise` object with the given block, execute it, and return the `:pending` object.
-
.fulfill(value, opts = {}) ⇒ Promise
Create a new ‘Promise` and fulfill it immediately.
-
.reject(reason, opts = {}) ⇒ Promise
Create a new ‘Promise` and reject it immediately.
-
.zip(*promises) ⇒ Promise<Array>
Builds a promise that produces the result of promises in an Array and fails if any of them fails.
Instance Method Summary collapse
-
#execute ⇒ Promise
Execute an ‘:unscheduled` `Promise`.
-
#fail(reason = StandardError.new) ⇒ IVar
Set the ‘IVar` to failed due to some error and wake or notify all threads waiting on it.
-
#flat_map(&block) ⇒ Promise
Yield the successful result to the block that returns a promise.
-
#initialize(opts = {}) { ... } ⇒ Promise
constructor
Initialize a new Promise with the provided options.
-
#on_success { ... } ⇒ Promise
Chain onto this promise an action to be undertaken on success (fulfillment).
-
#rescue { ... } ⇒ Promise
(also: #catch, #on_error)
Chain onto this promise an action to be undertaken on failure (rejection).
-
#set(value = NULL) { ... } ⇒ IVar
Set the ‘IVar` to a value and wake or notify all threads waiting on it.
-
#then(*args) { ... } ⇒ Promise
Chain a new promise off the current promise.
-
#zip(*others) ⇒ Promise<Array>
Builds a promise that produces the result of self and others in an Array and fails if any of them fails.
Methods inherited from IVar
Methods included from Concern::Observable
#add_observer, #count_observers, #delete_observer, #delete_observers, #with_observer
Methods included from Concern::Obligation
#complete?, #exception, #fulfilled?, #incomplete?, #pending?, #reason, #rejected?, #state, #unscheduled?, #value, #value!, #wait, #wait!
Methods included from Concern::Dereferenceable
Constructor Details
#initialize(opts = {}) { ... } ⇒ Promise
Initialize a new Promise with the provided options.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 210 def initialize(opts = {}, &block) opts.delete_if { |k, v| v.nil? } super(NULL, opts.merge(__promise_body_from_block__: block), &nil) end |
Class Method Details
.all?(*promises) ⇒ Boolean
Aggregates a collection of promises and executes the ‘then` condition if all aggregated promises succeed. Executes the `rescue` handler with a `Concurrent::PromiseExecutionError` if any of the aggregated promises fail. Upon execution will execute any of the aggregate promises that were not already executed.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 464 def self.all?(*promises) aggregate(:all?, *promises) end |
.any?(*promises) ⇒ Promise
Aggregates a collection of promises and executes the ‘then` condition if any aggregated promises succeed. Executes the `rescue` handler with a `Concurrent::PromiseExecutionError` if any of the aggregated promises fail. Upon execution will execute any of the aggregate promises that were not already executed.
The returned promise will not yet have been executed. Additional ‘#then` and `#rescue` handlers may still be provided. Once the returned promise is execute the aggregate promises will be also be executed (if they have not been executed already). The results of the aggregate promises will be checked upon completion. The necessary `#then` and `#rescue` blocks on the aggregating promise will then be executed as appropriate. If the `#rescue` handlers are executed the raises exception will be `Concurrent::PromiseExecutionError`.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 475 def self.any?(*promises) aggregate(:any?, *promises) end |
.execute(opts = {}, &block) ⇒ Promise
Create a new ‘Promise` object with the given block, execute it, and return the `:pending` object.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 296 def self.execute(opts = {}, &block) new(opts, &block).execute end |
.fulfill(value, opts = {}) ⇒ Promise
Create a new ‘Promise` and fulfill it immediately.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 224 def self.fulfill(value, opts = {}) Promise.new(opts).tap { |p| p.send(:synchronized_set_state!, true, value, nil) } end |
.reject(reason, opts = {}) ⇒ Promise
Create a new ‘Promise` and reject it immediately.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 237 def self.reject(reason, opts = {}) Promise.new(opts).tap { |p| p.send(:synchronized_set_state!, false, nil, reason) } end |
.zip(*promises) ⇒ Promise<Array> .zip(*promises, opts) ⇒ Promise<Array>
Builds a promise that produces the result of promises in an Array and fails if any of them fails.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 409 def self.zip(*promises) opts = promises.last.is_a?(::Hash) ? promises.pop.dup : {} opts[:executor] ||= ImmediateExecutor.new zero = if !opts.key?(:execute) || opts.delete(:execute) fulfill([], opts) else Promise.new(opts) { [] } end promises.reduce(zero) do |p1, p2| p1.flat_map do |results| p2.then do |next_result| results << next_result end end end end |
Instance Method Details
#execute ⇒ Promise
Execute an ‘:unscheduled` `Promise`. Immediately sets the state to `:pending` and passes the block to a new thread/thread pool for eventual execution. Does nothing if the `Promise` is in any state other than `:unscheduled`.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 246 def execute if root? if compare_and_set_state(:pending, :unscheduled) set_pending realize(@promise_body) end else compare_and_set_state(:pending, :unscheduled) @parent.execute end self end |
#fail(reason = StandardError.new) ⇒ IVar
Set the ‘IVar` to failed due to some error and wake or notify all threads waiting on it.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 278 def fail(reason = StandardError.new) set { raise reason } end |
#flat_map(&block) ⇒ Promise
Yield the successful result to the block that returns a promise. If that promise is also successful the result is the result of the yielded promise. If either part fails the whole also fails.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 375 def flat_map(&block) child = Promise.new( parent: self, executor: ImmediateExecutor.new, ) on_error { |e| child.on_reject(e) } on_success do |result1| begin inner = block.call(result1) inner.execute inner.on_success { |result2| child.on_fulfill(result2) } inner.on_error { |e| child.on_reject(e) } rescue => e child.on_reject(e) end end child end |
#on_success { ... } ⇒ Promise
Chain onto this promise an action to be undertaken on success (fulfillment).
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 349 def on_success(&block) raise ArgumentError.new('no block given') unless block_given? self.then(&block) end |
#rescue { ... } ⇒ Promise Also known as: catch, on_error
Chain onto this promise an action to be undertaken on failure (rejection).
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 360 def rescue(&block) self.then(block) end |
#set(value = NULL) { ... } ⇒ IVar
Set the ‘IVar` to a value and wake or notify all threads waiting on it.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 262 def set(value = NULL, &block) raise PromiseExecutionError.new('supported only on root promise') unless root? check_for_block_or_value!(block_given?, value) synchronize do if @state != :unscheduled raise MultipleAssignmentError else @promise_body = block || Proc.new { |result| value } end end execute end |
#then(rescuer, executor, &block) ⇒ Promise #then(rescuer, executor: executor, &block) ⇒ Promise
Chain a new promise off the current promise.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 314 def then(*args, &block) if args.last.is_a?(::Hash) executor = args.pop[:executor] rescuer = args.first else rescuer, executor = args end executor ||= @executor raise ArgumentError.new('rescuers and block are both missing') if rescuer.nil? && !block_given? block = Proc.new { |result| result } unless block_given? child = Promise.new( parent: self, executor: executor, on_fulfill: block, on_reject: rescuer ) synchronize do child.state = :pending if @state == :pending child.on_fulfill((@value)) if @state == :fulfilled child.on_reject(@reason) if @state == :rejected @children << child end child end |
#zip(*promises) ⇒ Promise<Array> #zip(*promises, opts) ⇒ Promise<Array>
Builds a promise that produces the result of self and others in an Array and fails if any of them fails.
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# File 'lib/rubypitaya/app-template/vendor/bundle/ruby/3.1.0/gems/concurrent-ruby-1.1.10/lib/concurrent-ruby/concurrent/promise.rb', line 440 def zip(*others) self.class.zip(self, *others) end |