class Ractor::Wrapper
An experimental class that wraps a non-shareable object, allowing multiple Ractors to access it concurrently.
WARNING: This is a highly experimental library, and currently not recommended for production use. (As of Ruby 3.0.0, the same can be said of Ractors in general.)
## What is Ractor::Wrapper
?
Ractors for the most part cannot access objects concurrently with other Ractors unless the object is shareable (that is, deeply immutable along with a few other restrictions.) If multiple Ractors need to interact with a shared resource that is stateful or otherwise not Ractor-shareable, that resource must itself be implemented and accessed as a Ractor
.
`Ractor::Wrapper` makes it possible for such a shared resource to be implemented as an object and accessed using ordinary method calls. It does this by “wrapping” the object in a Ractor
, and mapping method calls to message passing. This may make it easier to implement such a resource with a simple class rather than a full-blown Ractor
with message passing, and it may also useful for adapting existing legacy object-based implementations.
Given a shared resource object, `Ractor::Wrapper` starts a new Ractor
and “runs” the object within that Ractor
. It provides you with a stub object on which you can invoke methods. The wrapper responds to these method calls by sending messages to the internal Ractor
, which invokes the shared object and then sends back the result. If the underlying object is thread-safe, you can configure the wrapper to run multiple threads that can run methods concurrently. Or, if not, the wrapper can serialize requests to the object.
## Example usage
The following example shows how to share a single `Faraday::Conection` object among multiple Ractors. Because `Faraday::Connection` is not itself thread-safe, this example serializes all calls to it.
require "faraday" # Create a Faraday connection and a wrapper for it. connection = Faraday.new "http://example.com" wrapper = Ractor::Wrapper.new(connection) # At this point, the connection object cannot be accessed directly # because it has been "moved" to the wrapper's internal Ractor. # connection.get("/whoops") # <= raises an error # However, any number of Ractors can now access it through the wrapper. # By default, access to the object is serialized; methods will not be # invoked concurrently. r1 = Ractor.new(wrapper) do |w| 10.times do w.stub.get("/hello") end :ok end r2 = Ractor.new(wrapper) do |w| 10.times do w.stub.get("/ruby") end :ok end # Wait for the two above Ractors to finish. r1.take r2.take # After you stop the wrapper, you can retrieve the underlying # connection object and access it directly again. wrapper.async_stop connection = wrapper.recover_object connection.get("/finally")
## Features
-
Provides a method interface to an object running in a different
Ractor
. -
Supports arbitrary method arguments and return values.
-
Supports exceptions thrown by the method.
-
Can be configured to copy or move arguments, return values, and exceptions, per method.
-
Can serialize method calls for non-concurrency-safe objects, or run methods concurrently in multiple worker threads for thread-safe objects.
-
Can gracefully shut down the wrapper and retrieve the original object.
## Caveats
Ractor::Wrapper
is subject to some limitations (and bugs) of Ractors, as of Ruby 3.0.0.
-
You cannot pass blocks to wrapped methods.
-
Certain types cannot be used as method arguments or return values because
Ractor
does not allow them to be moved between Ractors. These include threads, procs, backtraces, and a few others. -
You can call wrapper methods from multiple Ractors concurrently, but you cannot call them from multiple Threads within a single
Ractor
. (This is due to bugs.ruby-lang.org/issues/17624) -
If you close the incoming port on a
Ractor
, it will no longer be able to call out via a wrapper. If you close its incoming port while a call is currently pending, that call may hang. (This is due to bugs.ruby-lang.org/issues/17617)
Constants
- VERSION
The version of the ractor-wrapper gem
@return [String]
Attributes
Return whether logging is enabled for this wrapper.
@return [Boolean]
Return the name of this wrapper.
@return [String, nil]
Return the wrapper stub. This is an object that responds to the same methods as the wrapped object, providing an easy way to call a wrapper.
@return [Ractor::Wrapper::Stub]
Return the number of threads used by the wrapper.
@return [Integer]
Public Class Methods
Create a wrapper around the given object.
If you pass an optional block, the wrapper itself will be yielded to it at which time you can set additional configuration options. (The configuration is frozen once the object is constructed.)
@param object [Object] The non-shareable object to wrap. @param threads [Integer] The number of worker threads to run.
Defaults to 1, which causes the worker to serialize calls.
# File lib/ractor/wrapper.rb, line 118 def initialize(object, threads: 1, move: false, move_arguments: nil, move_return: nil, logging: false, name: nil) @method_settings = {} self.threads = threads self.logging = logging self.name = name configure_method(move: move, move_arguments: move_arguments, move_return: move_return) yield self if block_given? @method_settings.freeze maybe_log("Starting server") @ractor = ::Ractor.new(name: name) { Server.new.run } opts = { object: object, threads: @threads, method_settings: @method_settings, name: @name, logging: @logging, } @ractor.send(opts, move: true) maybe_log("Server ready") @stub = Stub.new(self) freeze end
Public Instance Methods
Request that the wrapper stop. All currently running calls will complete before the wrapper actually terminates. However, any new calls will fail.
This metnod is idempotent and can be called multiple times (even from different ractors).
@return [self]
# File lib/ractor/wrapper.rb, line 294 def async_stop maybe_log("Stopping #{name}") @ractor.send(Message.new(:stop)) self rescue ::Ractor::ClosedError # Ignore to allow stops to be idempotent. self end
A lower-level interface for calling methods through the wrapper.
@param method_name [Symbol] The name of the method to call @param args [arguments] The positional arguments @param kwargs [keywords] The keyword arguments @return [Object] The return value
# File lib/ractor/wrapper.rb, line 268 def call(method_name, *args, **kwargs) request = Message.new(:call, data: [method_name, args, kwargs]) transaction = request.transaction move = method_settings(method_name).move_arguments? maybe_log("Sending method #{method_name} (move=#{move}, transaction=#{transaction})") @ractor.send(request, move: move) reply = ::Ractor.receive_if { |msg| msg.is_a?(Message) && msg.transaction == transaction } case reply.type when :result maybe_log("Received result for method #{method_name} (transaction=#{transaction})") reply.data when :error maybe_log("Received exception for method #{method_name} (transaction=#{transaction})") raise reply.data end end
Configure the move semantics for the given method (or the default settings if no method name is given.) That is, determine whether arguments, return values, and/or exceptions are copied or moved when communicated with the wrapper. By default, all objects are copied.
This method can be called only during an initialization block. All settings are frozen once the wrapper is active.
@param method_name [Symbol, nil] The name of the method being configured,
or `nil` to set defaults for all methods not configured explicitly.
@param move [Boolean] Whether to move all communication. This value, if
given, is used if `move_arguments`, `move_return`, or `move_exceptions` are not set.
@param move_arguments [Boolean] Whether to move arguments. @param move_return [Boolean] Whether to move return values.
# File lib/ractor/wrapper.rb, line 208 def configure_method(method_name = nil, move: false, move_arguments: nil, move_return: nil) method_name = method_name.to_sym unless method_name.nil? @method_settings[method_name] = MethodSettings.new(move: move, move_arguments: move_arguments, move_return: move_return) end
Enable or disable internal debug logging.
This method can be called only during an initialization block. All settings are frozen once the wrapper is active.
@param value [Boolean]
# File lib/ractor/wrapper.rb, line 174 def logging=(value) @logging = value ? true : false end
Return the method settings for the given method name. This returns the default method settings if the given method is not configured explicitly by name.
@param method_name [Symbol,nil] The method name, or `nil` to return the
defaults.
@return [MethodSettings]
# File lib/ractor/wrapper.rb, line 255 def method_settings(method_name) method_name = method_name.to_sym @method_settings[method_name] || @method_settings[nil] end
Set the name of this wrapper. This is shown in logging, and is also used as the name of the wrapping Ractor
.
This method can be called only during an initialization block. All settings are frozen once the wrapper is active.
@param value [String, nil]
# File lib/ractor/wrapper.rb, line 187 def name=(value) @name = value ? value.to_s.freeze : nil end
Retrieves the original object that was wrapped. This should be called only after a stop request has been issued using {#async_stop}, and may block until the wrapper has fully stopped.
Only one ractor may call this method; any additional calls will fail.
@return [Object] The original wrapped object
# File lib/ractor/wrapper.rb, line 312 def recovered_object @ractor.take end
Set the number of threads to run in the wrapper. If the underlying object is thread-safe, this allows concurrent calls to it. If the underlying object is not thread-safe, you should leave this set to its default of 1, which effectively causes calls to be serialized.
This method can be called only during an initialization block. All settings are frozen once the wrapper is active.
@param value [Integer]
# File lib/ractor/wrapper.rb, line 160 def threads=(value) value = value.to_i value = 1 if value < 1 @threads = value end
Private Instance Methods
# File lib/ractor/wrapper.rb, line 318 def maybe_log(str) return unless logging time = ::Time.now.utc.strftime("%Y-%m-%dT%H:%M:%S.%L") $stderr.puts("[#{time} Ractor::Wrapper/#{name}]: #{str}") $stderr.flush end