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.join # 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.join
# Here, "I am in Ractor! a=1" is printed

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 can be received with Ractor#value.

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

[] (sym)

Source

# File ractor.rb, line 453
def self.[](sym)
  Primitive.ractor_local_value(sym)
end

get a value from ractor-local storage of current Ractor

[]= (sym, val)

Source

# File ractor.rb, line 458
def self.[]=(sym, val)
  Primitive.ractor_local_value_set(sym, val)
end

set a value in ractor-local storage of current Ractor

count ()

Source

# File ractor.rb, line 260
def self.count
  __builtin_cexpr! %q{
    ULONG2NUM(GET_VM()->ractor.cnt);
  }
end

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

current ()

Source

# File ractor.rb, line 246
def self.current
  __builtin_cexpr! %q{
    rb_ractor_self(rb_ec_ractor_ptr(ec));
  }
end

Returns the currently executing Ractor.

Ractor.current #=> #<Ractor:#1 running>

main ()

Source

# File ractor.rb, line 481
def self.main
  __builtin_cexpr! %q{
    rb_ractor_self(GET_VM()->ractor.main_ractor);
  }
end

returns main ractor

main? ()

Source

# File ractor.rb, line 488
def self.main?
  __builtin_cexpr! %q{
    RBOOL(GET_VM()->ractor.main_ractor == rb_ec_ractor_ptr(ec))
  }
end

return true if the current ractor is main ractor

make_shareable(obj, copy: false) → shareable_obj

Source

# File ractor.rb, line 422
def self.make_shareable obj, copy: false
  if copy
    __builtin_cexpr! %q{
      rb_ractor_make_shareable_copy(obj);
    }
  else
    __builtin_cexpr! %q{
      rb_ractor_make_shareable(obj);
    }
  end
end

Make obj shareable between ractors.

obj and all the objects it refers to will be frozen, unless they are already shareable.

If copy keyword is true, it will copy objects before freezing them, and will not modify obj or its internal objects.

Note that the specification and implementation of this method are not mature and may be changed in the future.

obj = ['test']
Ractor.shareable?(obj)     #=> false
Ractor.make_shareable(obj) #=> ["test"]
Ractor.shareable?(obj)     #=> true
obj.frozen?                #=> true
obj[0].frozen?             #=> true

# Copy vs non-copy versions:
obj1 = ['test']
obj1s = Ractor.make_shareable(obj1)
obj1.frozen?                        #=> true
obj1s.object_id == obj1.object_id   #=> true
obj2 = ['test']
obj2s = Ractor.make_shareable(obj2, copy: true)
obj2.frozen?                        #=> false
obj2s.frozen?                       #=> true
obj2s.object_id == obj2.object_id   #=> false
obj2s[0].object_id == obj2[0].object_id #=> false

See also the “Shareable and unshareable objects” section in the Ractor class docs.

new(*args, name: nil) {|*args| block } → ractor

Source

# File ractor.rb, line 231
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)")
    Kernel.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

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>

receive → obj

Source

# File ractor.rb, line 312
def self.receive
  Ractor.current.default_port.receive
end

Receive a message from the default port.

Also aliased as: recv

recv

Alias for: receive

select(*ports) → [...]

Source

# File ractor.rb, line 271
def self.select(*ports)
  raise ArgumentError, 'specify at least one ractor or `yield_value`' if ports.empty?

  monitors = {} # Ractor::Port => Ractor

  ports = ports.map do |arg|
    case arg
    when Ractor
      port = Ractor::Port.new
      monitors[port] = arg
      arg.monitor port
      port
    when Ractor::Port
      arg
    else
      raise ArgumentError, "should be Ractor::Port or Ractor"
    end
  end

  begin
    result_port, obj = __builtin_ractor_select_internal(ports)

    if r = monitors[result_port]
      [r, r.value]
    else
      [result_port, obj]
    end
  ensure
    # close all ports for join
    monitors.each do |port, r|
      r.unmonitor port
      port.close
    end
  end
end

TBD

shareable?(obj) → true | false

Source

# File ractor.rb, line 381
def self.shareable? obj
  __builtin_cexpr! %q{
    RBOOL(rb_ractor_shareable_p(obj));
  }
end

Checks if the object is shareable by ractors.

Ractor.shareable?(1)            #=> true -- numbers and other immutable basic values are frozen
Ractor.shareable?('foo')        #=> false, unless the string is frozen due to # frozen_string_literal: true
Ractor.shareable?('foo'.freeze) #=> true

See also the “Shareable and unshareable objects” section in the Ractor class docs.

store_if_absent(key){ init_block }

Source

# File ractor.rb, line 476
def self.store_if_absent(sym)
  Primitive.ractor_local_value_store_if_absent(sym)
end

If the corresponding value is not set, yield a value with init_block and store the value in thread-safe manner. This method returns corresponding stored value.

(1..10).map{
  Thread.new(it){|i|
    Ractor.store_if_absent(:s){ f(); i }
    #=> return stored value of key :s
  }
}.map(&:value).uniq.size #=> 1 and f() is called only once

Public Instance Methods

Alias for: send

[] (sym)

Source

# File ractor.rb, line 436
def [](sym)
  if (self != Ractor.current)
    raise RuntimeError, "Cannot get ractor local storage for non-current ractor"
  end
  Primitive.ractor_local_value(sym)
end

get a value from ractor-local storage for current Ractor Obsolete and use Ractor.[] instead.

[]= (sym, val)

Source

# File ractor.rb, line 445
def []=(sym, val)
  if (self != Ractor.current)
    raise RuntimeError, "Cannot set ractor local storage for non-current ractor"
  end
  Primitive.ractor_local_value_set(sym, val)
end

set a value in ractor-local storage for current Ractor Obsolete and use Ractor.[]= instead.

current.close → true | false

Source

# File ractor.rb, line 366
def close
  default_port.close
end

Closes default_port. Closing port is allowed only by the ractor which creates this port. So this close method also allowed by the current Ractor.

default_port → port object

Source

# File ractor.rb, line 528
def default_port
  __builtin_cexpr! %q{
    ractor_default_port_value(RACTOR_PTR(self))
  }
end

return default port of the Ractor.

inspect ()

Source

# File ractor.rb, line 337
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

Also aliased as: to_s

join → self

Source

# File ractor.rb, line 547
def join
  port = Port.new

  self.monitor port
  if port.receive == :aborted
    __builtin_ractor_value
  end

  self
ensure
  port.close
end

Wait for the termination of the Ractor. If the Ractor was aborted (terminated with an exception), Ractor#value is called to raise an exception.

Ractor.new{}.join #=> ractor

Ractor.new{ raise "foo" }.join
#=> raise an exception "foo (RuntimeError)"

monitor(port) → self

Source

# File ractor.rb, line 601
def monitor port
  __builtin_ractor_monitor(port)
end

Register port as a monitoring port. If the ractor terminated, the port received a Symbol object. :exited will be sent if the ractor terminated without an exception. :aborted will be sent if the ractor terminated with a exception.

r = Ractor.new{ some_task() }
r.monitor(port = Ractor::Port.new)
port.receive #=> :exited and r is terminated

r = Ractor.new{ raise "foo" }
r.monitor(port = Ractor::Port.new)
port.receive #=> :terminated and r is terminated with an exception "foo"

name ()

Source

# File ractor.rb, line 350
def name
  __builtin_cexpr! %q{RACTOR_PTR(self)->name}
end

The name set in Ractor.new, or nil.

recv ()

Alias for: receive

send(msg) → self

Source

# File ractor.rb, line 331
def send(...)
  default_port.send(...)
  self
end

It is equivalent to default_port.send(msg)

Also aliased as: <<

take ()

Source

# File ractor.rb, line 579
def take
  Kernel.warn("Ractor#take was deprecated and use Ractor#value instead. This method will be removed after the end of Aug 2025", uplevel: 0)
  self.value
end

keep it for compatibility

to_s ()

Alias for: inspect

unmonitor(port) → self

Source

# File ractor.rb, line 611
def unmonitor port
  __builtin_ractor_unmonitor(port)
end

Unregister port from the monitoring ports.

value → obj

Source

# File ractor.rb, line 573
def value
  self.join
  __builtin_ractor_value
end

Waits for ractor to complete, using join, and return its value or raise the exception which terminated the Ractor. The value will not be copied even if it is unshareable object. Therefore at most 1 Ractor can get a value.

r = Ractor.new{ [1, 2] }
r.value #=> [1, 2] (unshareable object)

Ractor.new(r){|r| r.value} #=> Ractor::Error

Private Instance Methods

receive ()

Source

# File ractor.rb, line 321
        def receive
  default_port.receive
end

same as Ractor.receive

Also aliased as: recv