class Ractor
Ractor is an Actor-model abstraction for Ruby that provides thread-safe parallel execution.
Ractor.new
makes a new Ractor, which can run in parallel.
# The simplest ractor r = Ractor.new {puts "I am in Ractor!"} r.take # wait for it to finish # Here, "I am in Ractor!" is printed
Ractors do not share all objects with each other. There are two main benefits to this: across ractors, thread-safety concerns such as data-races and race-conditions are not possible. The other benefit is parallelism.
To achieve this, object sharing is limited across ractors. For example, unlike in threads, ractors can’t access all the objects available in other ractors. Even objects normally available through variables in the outer scope are prohibited from being used across ractors.
a = 1 r = Ractor.new {puts "I am in Ractor! a=#{a}"} # fails immediately with # ArgumentError (can not isolate a Proc because it accesses outer variables (a).)
The object must be explicitly shared:
a = 1 r = Ractor.new(a) { |a1| puts "I am in Ractor! a=#{a1}"}
On CRuby (the default implementation), Global Virtual Machine Lock (GVL) is held per ractor, so ractors can perform in parallel without locking each other. This is unlike the situation with threads on CRuby.
Instead of accessing shared state, objects should be passed to and from ractors by sending and receiving them as messages.
a = 1 r = Ractor.new do a_in_ractor = receive # receive blocks until somebody passes a message puts "I am in Ractor! a=#{a_in_ractor}" end r.send(a) # pass it r.take # Here, "I am in Ractor! a=1" is printed
There are two pairs of methods for sending/receiving messages:
-
Ractor#send
andRactor.receive
for when the sender knows the receiver (push); -
Ractor.yield
andRactor#take
for when the receiver knows the sender (pull);
In addition to that, any arguments passed to Ractor.new
are passed to the block and available there as if received by Ractor.receive
, and the last block value is sent outside of the ractor as if sent by Ractor.yield
.
A little demonstration of a classic ping-pong:
server = Ractor.new(name: "server") do puts "Server starts: #{self.inspect}" puts "Server sends: ping" Ractor.yield 'ping' # The server doesn't know the receiver and sends to whoever interested received = Ractor.receive # The server doesn't know the sender and receives from whoever sent puts "Server received: #{received}" end client = Ractor.new(server) do |srv| # The server is sent to the client, and available as srv puts "Client starts: #{self.inspect}" received = srv.take # The client takes a message from the server puts "Client received from " \ "#{srv.inspect}: #{received}" puts "Client sends to " \ "#{srv.inspect}: pong" srv.send 'pong' # The client sends a message to the server end [client, server].each(&:take) # Wait until they both finish
This will output something like:
Server starts: #<Ractor:#2 server test.rb:1 running> Server sends: ping Client starts: #<Ractor:#3 test.rb:8 running> Client received from #<Ractor:#2 server test.rb:1 blocking>: ping Client sends to #<Ractor:#2 server test.rb:1 blocking>: pong Server received: pong
Ractors receive their messages via the incoming port, and send them to the outgoing port. Either one can be disabled with Ractor#close_incoming
and Ractor#close_outgoing
, respectively. When a ractor terminates, its ports are closed automatically.
Shareable and unshareable objects¶ ↑
When an object is sent to and from a ractor, it’s important to understand whether the object is shareable or unshareable. Most Ruby objects are unshareable objects. Even frozen objects can be unshareable if they contain (through their instance variables) unfrozen objects.
Shareable objects are those which can be used by several threads without compromising thread-safety, for example numbers, true
and false
. Ractor.shareable?
allows you to check this, and Ractor.make_shareable
tries to make the object shareable if it’s not already, and gives an error if it can’t do it.
Ractor.shareable?(1) #=> true -- numbers and other immutable basic values are shareable Ractor.shareable?('foo') #=> false, unless the string is frozen due to # frozen_string_literal: true Ractor.shareable?('foo'.freeze) #=> true Ractor.shareable?([Object.new].freeze) #=> false, inner object is unfrozen ary = ['hello', 'world'] ary.frozen? #=> false ary[0].frozen? #=> false Ractor.make_shareable(ary) ary.frozen? #=> true ary[0].frozen? #=> true ary[1].frozen? #=> true
When a shareable object is sent (via send
or Ractor.yield
), no additional processing occurs on it. It just becomes usable by both ractors. When an unshareable object is sent, it can be either copied or moved. The first is the default, and it copies the object fully by deep cloning (Object#clone
) the non-shareable parts of its structure.
data = ['foo', 'bar'.freeze] r = Ractor.new do data2 = Ractor.receive puts "In ractor: #{data2.object_id}, #{data2[0].object_id}, #{data2[1].object_id}" end r.send(data) r.take puts "Outside : #{data.object_id}, #{data[0].object_id}, #{data[1].object_id}"
This will output something like:
In ractor: 340, 360, 320 Outside : 380, 400, 320
Note that the object ids of the array and the non-frozen string inside the array have changed in the ractor because they are different objects. The second array’s element, which is a shareable frozen string, is the same object.
Deep cloning of objects may be slow, and sometimes impossible. Alternatively, move: true
may be used during sending. This will move the unshareable object to the receiving ractor, making it inaccessible to the sending ractor.
data = ['foo', 'bar'] r = Ractor.new do data_in_ractor = Ractor.receive puts "In ractor: #{data_in_ractor.object_id}, #{data_in_ractor[0].object_id}" end r.send(data, move: true) r.take puts "Outside: moved? #{Ractor::MovedObject === data}" puts "Outside: #{data.inspect}"
This will output:
In ractor: 100, 120 Outside: moved? true test.rb:9:in `method_missing': can not send any methods to a moved object (Ractor::MovedError)
Notice that even inspect
(and more basic methods like __id__
) is inaccessible on a moved object.
Class
and Module
objects are shareable so the class/module definitions are shared between ractors. Ractor objects are also shareable. All operations on shareable objects are thread-safe, so the thread-safety property will be kept. We can not define mutable shareable objects in Ruby, but C extensions can introduce them.
It is prohibited to access (get) instance variables of shareable objects in other ractors if the values of the variables aren’t shareable. This can occur because modules/classes are shareable, but they can have instance variables whose values are not. In non-main ractors, it’s also prohibited to set instance variables on classes/modules (even if the value is shareable).
class C class << self attr_accessor :tricky end end C.tricky = "unshareable".dup r = Ractor.new(C) do |cls| puts "I see #{cls}" puts "I can't see #{cls.tricky}" cls.tricky = true # doesn't get here, but this would also raise an error end r.take # I see C # can not access instance variables of classes/modules from non-main Ractors (RuntimeError)
Ractors can access constants if they are shareable. The main Ractor is the only one that can access non-shareable constants.
GOOD = 'good'.freeze BAD = 'bad'.dup r = Ractor.new do puts "GOOD=#{GOOD}" puts "BAD=#{BAD}" end r.take # GOOD=good # can not access non-shareable objects in constant Object::BAD by non-main Ractor. (NameError) # Consider the same C class from above r = Ractor.new do puts "I see #{C}" puts "I can't see #{C.tricky}" end r.take # I see C # can not access instance variables of classes/modules from non-main Ractors (RuntimeError)
See also the description of # shareable_constant_value
pragma in Comments syntax explanation.
Ractors vs threads¶ ↑
Each ractor has its own main Thread
. New threads can be created from inside ractors (and, on CRuby, they share the GVL with other threads of this ractor).
r = Ractor.new do a = 1 Thread.new {puts "Thread in ractor: a=#{a}"}.join end r.take # Here "Thread in ractor: a=1" will be printed
Note on code examples¶ ↑
In the examples below, sometimes we use the following method to wait for ractors that are not currently blocked to finish (or to make progress).
def wait sleep(0.1) end
It is **only for demonstration purposes** and shouldn’t be used in a real code. Most of the time, take
is used to wait for ractors to finish.
Reference¶ ↑
See Ractor design doc for more details.
Public Class Methods
Returns the number of Ractors currently running or blocking (waiting).
Ractor.count #=> 1 r = Ractor.new(name: 'example') { Ractor.yield(1) } Ractor.count #=> 2 (main + example ractor) r.take # wait for Ractor.yield(1) r.take # wait until r will finish Ractor.count #=> 1
# File ruby_3_3_3/ractor.rb, line 302 def self.count __builtin_cexpr! %q{ ULONG2NUM(GET_VM()->ractor.cnt); } end
Returns the currently executing Ractor
.
Ractor.current #=> #<Ractor:#1 running>
# File ruby_3_3_3/ractor.rb, line 288 def self.current __builtin_cexpr! %q{ rb_ractor_self(rb_ec_ractor_ptr(ec)); } end
returns main ractor
# File ruby_3_3_3/ractor.rb, line 848 def self.main __builtin_cexpr! %q{ rb_ractor_self(GET_VM()->ractor.main_ractor); } end
Create a new Ractor with args and a block.
The given block (Proc
) will be isolated (can’t access any outer variables). self
inside the block will refer to the current Ractor.
r = Ractor.new { puts "Hi, I am #{self.inspect}" } r.take # Prints "Hi, I am #<Ractor:#2 test.rb:1 running>"
Any args
passed are propagated to the block arguments by the same rules as objects sent via send
/Ractor.receive. If an argument in args
is not shareable, it will be copied (via deep cloning, which might be inefficient).
arg = [1, 2, 3] puts "Passing: #{arg} (##{arg.object_id})" r = Ractor.new(arg) {|received_arg| puts "Received: #{received_arg} (##{received_arg.object_id})" } r.take # Prints: # Passing: [1, 2, 3] (#280) # Received: [1, 2, 3] (#300)
Ractor’s name
can be set for debugging purposes:
r = Ractor.new(name: 'my ractor') {}; r.take p r #=> #<Ractor:#3 my ractor test.rb:1 terminated>
# File ruby_3_3_3/ractor.rb, line 273 def self.new(*args, name: nil, &block) b = block # TODO: builtin bug raise ArgumentError, "must be called with a block" unless block if __builtin_cexpr!("RBOOL(ruby_single_main_ractor)") warn("Ractor is experimental, and the behavior may change in future versions of Ruby! " \ "Also there are many implementation issues.", uplevel: 0, category: :experimental) end loc = caller_locations(1, 1).first loc = "#{loc.path}:#{loc.lineno}" __builtin_ractor_create(loc, name, args, b) end
Receive a message from the incoming port of the current ractor (which was sent there by send
from another ractor).
r = Ractor.new do v1 = Ractor.receive puts "Received: #{v1}" end r.send('message1') r.take # Here will be printed: "Received: message1"
Alternatively, the private instance method receive
may be used:
r = Ractor.new do v1 = receive puts "Received: #{v1}" end r.send('message1') r.take # This prints: "Received: message1"
The method blocks if the queue is empty.
r = Ractor.new do puts "Before first receive" v1 = Ractor.receive puts "Received: #{v1}" v2 = Ractor.receive puts "Received: #{v2}" end wait puts "Still not received" r.send('message1') wait puts "Still received only one" r.send('message2') r.take
Output:
Before first receive Still not received Received: message1 Still received only one Received: message2
If close_incoming
was called on the ractor, the method raises Ractor::ClosedError
if there are no more messages in the incoming queue:
Ractor.new do close_incoming receive end wait # in `receive': The incoming port is already closed => #<Ractor:#2 test.rb:1 running> (Ractor::ClosedError)
# File ruby_3_3_3/ractor.rb, line 430 def self.receive __builtin_cexpr! %q{ ractor_receive(ec, rb_ec_ractor_ptr(ec)) } end
Receive only a specific message.
Instead of Ractor.receive
, Ractor.receive_if
can be given a pattern (or any filter) in a block and you can choose the messages to accept that are available in your ractor’s incoming queue.
r = Ractor.new do p Ractor.receive_if{|msg| msg.match?(/foo/)} #=> "foo3" p Ractor.receive_if{|msg| msg.match?(/bar/)} #=> "bar1" p Ractor.receive_if{|msg| msg.match?(/baz/)} #=> "baz2" end r << "bar1" r << "baz2" r << "foo3" r.take
This will output:
foo3 bar1 baz2
If the block returns a truthy value, the message is removed from the incoming queue and returned. Otherwise, the message remains in the incoming queue and the next messages are checked by the given block.
If there are no messages left in the incoming queue, the method will block until new messages arrive.
If the block is escaped by break/return/exception/throw, the message is removed from the incoming queue as if a truthy value had been returned.
r = Ractor.new do val = Ractor.receive_if{|msg| msg.is_a?(Array)} puts "Received successfully: #{val}" end r.send(1) r.send('test') wait puts "2 non-matching sent, nothing received" r.send([1, 2, 3]) wait
Prints:
2 non-matching sent, nothing received Received successfully: [1, 2, 3]
Note that you can not call receive/receive_if in the given block recursively. You should not do any tasks in the block other than message filtration.
Ractor.current << true Ractor.receive_if{|msg| Ractor.receive} #=> `receive': can not call receive/receive_if recursively (Ractor::Error)
# File ruby_3_3_3/ractor.rb, line 509 def self.receive_if &b Primitive.ractor_receive_if b end
Wait for any ractor to have something in its outgoing port, read from this ractor, and then return that ractor and the object received.
r1 = Ractor.new {Ractor.yield 'from 1'} r2 = Ractor.new {Ractor.yield 'from 2'} r, obj = Ractor.select(r1, r2) puts "received #{obj.inspect} from #{r.inspect}" # Prints: received "from 1" from #<Ractor:#2 test.rb:1 running> # But could just as well print "from r2" here, either prints could be first.
If one of the given ractors is the current ractor, and it is selected, r
will contain the :receive
symbol instead of the ractor object.
r1 = Ractor.new(Ractor.current) do |main| main.send 'to main' Ractor.yield 'from 1' end r2 = Ractor.new do Ractor.yield 'from 2' end r, obj = Ractor.select(r1, r2, Ractor.current) puts "received #{obj.inspect} from #{r.inspect}" # Could print: received "to main" from :receive
If yield_value
is provided, that value may be yielded if another ractor is calling take
. In this case, the pair [:yield, nil]
is returned:
r1 = Ractor.new(Ractor.current) do |main| puts "Received from main: #{main.take}" end puts "Trying to select" r, obj = Ractor.select(r1, Ractor.current, yield_value: 123) wait puts "Received #{obj.inspect} from #{r.inspect}"
This will print:
Trying to select Received from main: 123 Received nil from :yield
move
boolean flag defines whether yielded value will be copied (default) or moved.
# File ruby_3_3_3/ractor.rb, line 358 def self.select(*ractors, yield_value: yield_unspecified = true, move: false) raise ArgumentError, 'specify at least one ractor or `yield_value`' if yield_unspecified && ractors.empty? if ractors.delete Ractor.current do_receive = true else do_receive = false end __builtin_ractor_select_internal ractors, do_receive, !yield_unspecified, yield_value, move end
Send a message to the current ractor’s outgoing port to be accepted by take
.
r = Ractor.new {Ractor.yield 'Hello from ractor'} puts r.take # Prints: "Hello from ractor"
This method is blocking, and will return only when somebody consumes the sent message.
r = Ractor.new do Ractor.yield 'Hello from ractor' puts "Ractor: after yield" end wait puts "Still not taken" puts r.take
This will print:
Still not taken Hello from ractor Ractor: after yield
If the outgoing port was closed with close_outgoing
, the method will raise:
r = Ractor.new do close_outgoing Ractor.yield 'Hello from ractor' end wait # `yield': The outgoing-port is already closed (Ractor::ClosedError)
The meaning of the move
argument is the same as for send
.
# File ruby_3_3_3/ractor.rb, line 643 def self.yield(obj, move: false) __builtin_cexpr! %q{ ractor_yield(ec, rb_ec_ractor_ptr(ec), obj, move) } end
Public Instance Methods
get a value from ractor-local storage
# File ruby_3_3_3/ractor.rb, line 838 def [](sym) Primitive.ractor_local_value(sym) end
set a value in ractor-local storage
# File ruby_3_3_3/ractor.rb, line 843 def []=(sym, val) Primitive.ractor_local_value_set(sym, val) end
Closes the incoming port and returns whether it was already closed. All further attempts to Ractor.receive
in the ractor, and send
to the ractor will fail with Ractor::ClosedError
.
r = Ractor.new {sleep(500)} r.close_incoming #=> false r.close_incoming #=> true r.send('test') # Ractor::ClosedError (The incoming-port is already closed)
# File ruby_3_3_3/ractor.rb, line 749 def close_incoming __builtin_cexpr! %q{ ractor_close_incoming(ec, RACTOR_PTR(self)); } end
Closes the outgoing port and returns whether it was already closed. All further attempts to Ractor.yield
in the ractor, and take
from the ractor will fail with Ractor::ClosedError
.
r = Ractor.new {sleep(500)} r.close_outgoing #=> false r.close_outgoing #=> true r.take # Ractor::ClosedError (The outgoing-port is already closed)
# File ruby_3_3_3/ractor.rb, line 767 def close_outgoing __builtin_cexpr! %q{ ractor_close_outgoing(ec, RACTOR_PTR(self)); } end
# File ruby_3_3_3/ractor.rb, line 716 def inspect loc = __builtin_cexpr! %q{ RACTOR_PTR(self)->loc } name = __builtin_cexpr! %q{ RACTOR_PTR(self)->name } id = __builtin_cexpr! %q{ UINT2NUM(rb_ractor_id(RACTOR_PTR(self))) } status = __builtin_cexpr! %q{ rb_str_new2(ractor_status_str(RACTOR_PTR(self)->status_)) } "#<Ractor:##{id}#{name ? ' '+name : ''}#{loc ? " " + loc : ''} #{status}>" end
The name set in Ractor.new
, or nil
.
# File ruby_3_3_3/ractor.rb, line 729 def name __builtin_cexpr! %q{RACTOR_PTR(self)->name} end
Send a message to a Ractor’s incoming queue to be accepted by Ractor.receive
.
r = Ractor.new do value = Ractor.receive puts "Received #{value}" end r.send 'message' # Prints: "Received: message"
The method is non-blocking (will return immediately even if the ractor is not ready to receive anything):
r = Ractor.new {sleep(5)} r.send('test') puts "Sent successfully" # Prints: "Sent successfully" immediately
An attempt to send to a ractor which already finished its execution will raise Ractor::ClosedError
.
r = Ractor.new {} r.take p r # "#<Ractor:#6 (irb):23 terminated>" r.send('test') # Ractor::ClosedError (The incoming-port is already closed)
If close_incoming
was called on the ractor, the method also raises Ractor::ClosedError
.
r = Ractor.new do sleep(500) receive end r.close_incoming r.send('test') # Ractor::ClosedError (The incoming-port is already closed) # The error is raised immediately, not when the ractor tries to receive
If the obj
is unshareable, by default it will be copied into the receiving ractor by deep cloning. If move: true
is passed, the object is moved into the receiving ractor and becomes inaccessible to the sender.
r = Ractor.new {puts "Received: #{receive}"} msg = 'message' r.send(msg, move: true) r.take p msg
This prints:
Received: message in `p': undefined method `inspect' for #<Ractor::MovedObject:0x000055c99b9b69b8>
All references to the object and its parts will become invalid to the sender.
r = Ractor.new {puts "Received: #{receive}"} s = 'message' ary = [s] copy = ary.dup r.send(ary, move: true) s.inspect # Ractor::MovedError (can not send any methods to a moved object) ary.class # Ractor::MovedError (can not send any methods to a moved object) copy.class # => Array, it is different object copy[0].inspect # Ractor::MovedError (can not send any methods to a moved object) # ...but its item was still a reference to `s`, which was moved
If the object is shareable, move: true
has no effect on it:
r = Ractor.new {puts "Received: #{receive}"} s = 'message'.freeze r.send(s, move: true) s.inspect #=> "message", still available
# File ruby_3_3_3/ractor.rb, line 599 def send(obj, move: false) __builtin_cexpr! %q{ ractor_send(ec, RACTOR_PTR(self), obj, move) } end
Get a message from the ractor’s outgoing port, which was put there by Ractor.yield
or at ractor’s termination.
r = Ractor.new do Ractor.yield 'explicit yield' 'last value' end puts r.take #=> 'explicit yield' puts r.take #=> 'last value' puts r.take # Ractor::ClosedError (The outgoing-port is already closed)
The fact that the last value is also sent to the outgoing port means that take
can be used as an analog of Thread#join
(“just wait until ractor finishes”). However, it will raise if somebody has already consumed that message.
If the outgoing port was closed with close_outgoing
, the method will raise Ractor::ClosedError
.
r = Ractor.new do sleep(500) Ractor.yield 'Hello from ractor' end r.close_outgoing r.take # Ractor::ClosedError (The outgoing-port is already closed) # The error would be raised immediately, not when ractor will try to receive
If an uncaught exception is raised in the Ractor
, it is propagated by take as a Ractor::RemoteError
.
r = Ractor.new {raise "Something weird happened"} begin r.take rescue => e p e # => #<Ractor::RemoteError: thrown by remote Ractor.> p e.ractor == r # => true p e.cause # => #<RuntimeError: Something weird happened> end
Ractor::ClosedError
is a descendant of StopIteration
, so the termination of the ractor will break out of any loops that receive this message without propagating the error:
r = Ractor.new do 3.times {|i| Ractor.yield "message #{i}"} "finishing" end loop {puts "Received: " + r.take} puts "Continue successfully"
This will print:
Received: message 0 Received: message 1 Received: message 2 Received: finishing Continue successfully
# File ruby_3_3_3/ractor.rb, line 710 def take __builtin_cexpr! %q{ ractor_take(ec, RACTOR_PTR(self)) } end
Private Instance Methods
same as Ractor.receive
# File ruby_3_3_3/ractor.rb, line 441 def receive __builtin_cexpr! %q{ ractor_receive(ec, rb_ec_ractor_ptr(ec)) } end
same as Ractor.receive_if
# File ruby_3_3_3/ractor.rb, line 514 def receive_if &b Primitive.ractor_receive_if b end