class Ractor

Ractor is a Actor-model abstraction for Ruby that provides thread-safe parallel execution.

Ractor.new can make new Ractor and it will run in parallel.

# The simplest ractor r = Ractor.new {puts "I am in Ractor!"} r.take # wait it to finish # here "I am in Ractor!" would be printed

Ractors do not share usual objects, so the some kind of thread-safety concerns such as data-race, race-conditions are not available on multi-ractor programming.

To achieve this, ractors severely limit object sharing between different ractors. For example, unlike threads, ractors can't access each other's objects, nor any objects through variables of the outer scope.

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).)

On CRuby (the default implementation), Global Virtual Machine Lock (GVL) is held per ractor, so ractors are performed in parallel without locking each other.

Instead of accessing the shared state, the objects should be passed to and from ractors via sending and receiving objects as messages.

a = 1 r = Ractor.new do   a_in_ractor = receive # receive blocks till somebody will pass 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" would be printed

There are two pairs of methods for sending/receiving messages:

In addition to that, an argument to Ractor.new would be passed to block and available there as if received by Ractor.receive, and the last block value would be sent outside of the ractor as if sent by Ractor.yield.

A little demonstration on a classic ping-pong:

server = Ractor.new 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 inside client, and available as srv   puts "Client starts: #{self.inspect}"   received = srv.take                       # The Client takes a message specifically 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 specifically to the server end  [client, server].each(&:take)               # Wait till they both finish

This will output:

Server starts: #<Ractor:#2 test.rb:1 running> Server sends: ping Client starts: #<Ractor:#3 test.rb:8 running> Client received from #<Ractor:#2 rac.rb:1 blocking>: ping Client sends to #<Ractor:#2 rac.rb:1 blocking>: pong Server received: pong

It is said that Ractor receives messages via the incoming port, and sends them to the outgoing port. Either one can be disabled with Ractor#close_incoming and Ractor#close_outgoing respectively. If a ractor terminated, its ports will be closed automatically.

Shareable and unshareable objects ↑

When the object is sent to and from the ractor, it is important to understand whether the object is shareable or unshareable. Most of objects are unshareable objects.

Shareable objects are basically those which can be used by several threads without compromising thread-safety; e.g. immutable ones. Ractor.shareable? allows to check this, and Ractor.make_shareable tries to make object shareable if it is not.

Ractor.shareable?(1)            #=> true -- numbers and other immutable basic values are Ractor.shareable?('foo')        #=> false, unless the string is frozen due to # freeze_string_literals: true Ractor.shareable?('foo'.freeze) #=> true  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 happens, and 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 makes the object's full copy by deep cloning of 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:

In ractor: 340, 360, 320 Outside  : 380, 400, 320

(Note that object id of both array and non-frozen string inside array have changed inside the ractor, showing it is different objects. But the second array's element, which is a shareable frozen string, has the same object_id.)

Deep cloning of the objects may be slow, and sometimes impossible. Alternatively, move: true may be used on sending. This will move the object to the receiving ractor, making it inaccessible for a 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.

Besides frozen objects, there are shareable objects. Class and Module objects are shareable so the Class/Module definitons are shared between ractors. Ractor objects are also shareable objects. All operations for the shareable mutable 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 instance variables of mutable shareable objects (especially Modules and classes) from ractors other than main:

class C   class << self     attr_accessor :tricky   end end  C.tricky = 'test'  r = Ractor.new(C) do |cls|   puts "I see #{cls}"   puts "I can't see #{cls.tricky}" 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'  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 creates its own thread. New threads can be created from inside ractor (and, on CRuby, sharing 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 examples below, sometimes we use the following method to wait till ractors that are not currently blocked will finish (or process till next blocking) method.

def wait   sleep(0.1) end

It is **only for demonstration purposes** and shouldn't be used in a real code. Most of the times, just take is used to wait till ractor will finish.

Reference ↑

See Ractor desgin doc for more details.

Public Class Methods

count() click to toggle source

Returns total count of Ractors currently running.

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 till r will finish Ractor.count                   #=> 1 
# File ractor.rb, line 287 def self.count   __builtin_cexpr! %q{     ULONG2NUM(GET_VM()->ractor.cnt);   } end
current() click to toggle source

Returns the currently executing Ractor.

Ractor.current #=> #<Ractor:#1 running> 
# File ractor.rb, line 273 def self.current   __builtin_cexpr! %q{     rb_ractor_self(rb_ec_ractor_ptr(ec));   } end
main() click to toggle source

returns main ractor

# File ractor.rb, line 833 def self.main   __builtin_cexpr! %q{     rb_ractor_self(GET_VM()->ractor.main_ractor);   } end
make_shareable(obj, copy: false) → shareable_obj click to toggle source

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, the method will copy objects before freezing them This is safer option but it can take be slower.

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.

# File ractor.rb, line 810 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
new(*args, name: nil) {|*args| block } → ractor click to toggle source

Create a new Ractor with args and a block.

A block (Proc) will be isolated (can't access to 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>"

args passed to the method would be propagated to block args by the same rules as objects passed through send/Ractor.receive: if args are not shareable, they 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') {} p r #=> #<Ractor:#3 my ractor test.rb:1 terminated> 
# File ractor.rb, line 262 def self.new(*args, name: nil, &block)   b = block # TODO: builtin bug   raise ArgumentError, "must be called with a block" unless block   loc = caller_locations(1, 1).first   loc = "#{loc.path}:#{loc.lineno}"   __builtin_ractor_create(loc, name, args, b) end
receive → msg click to toggle source

Receive an incoming message from the current Ractor's incoming port's queue, which was sent there by send.

r = Ractor.new do   v1 = Ractor.receive   puts "Received: #{v1}" end r.send('message1') r.take # Here will be printed: "Received: message1"

Alternatively, private instance method receive may be used:

r = Ractor.new do   v1 = receive   puts "Received: #{v1}" end r.send('message1') r.take # Here will be printed: "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 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 ractor.rb, line 415 def self.receive   __builtin_cexpr! %q{     ractor_receive(ec, rb_ec_ractor_ptr(ec))   } end
Also aliased as: recv
receive_if {|msg| block } → msg click to toggle source

Receive only a specific message.

Instead of Ractor.receive, Ractor.receive_if can provide a pattern by a block and you can choose the receiving message.

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 will be removed from the incoming queue and returned. Otherwise, the messsage remains in the incoming queue and the following received 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. It means that you should not do any tasks in the block.

Ractor.current << true Ractor.receive_if{|msg| Ractor.receive} #=> `receive': can not call receive/receive_if recursively (Ractor::Error) 
# File ractor.rb, line 493 def self.receive_if &b   Primitive.ractor_receive_if b end
Alias for: receive
select(*ractors, [yield_value:, move: false]) → [ractor or symbol, obj] click to toggle source

Waits for the first ractor to have something in its outgoing port, reads from this ractor, and returns 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>

If one of the given ractors is the current ractor, and it would be selected, r will contain :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}" # Prints: 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] would be 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 should be copied (default) or moved.

# File ractor.rb, line 342 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?    __builtin_cstmt! %q{     const VALUE *rs = RARRAY_CONST_PTR_TRANSIENT(ractors);     VALUE rv;     VALUE v = ractor_select(ec, rs, RARRAY_LENINT(ractors),                             yield_unspecified == Qtrue ? Qundef : yield_value,                             (bool)RTEST(move) ? true : false, &rv);     return rb_ary_new_from_args(2, rv, v);   } end
shareable?(obj) → true | false click to toggle source

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 # freeze_string_literals: true Ractor.shareable?('foo'.freeze) #=> true

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

# File ractor.rb, line 769 def self.shareable? obj   __builtin_cexpr! %q{     rb_ractor_shareable_p(obj) ? Qtrue : Qfalse;   } end
yield(msg, move: false) → nil click to toggle source

Send a message to the current ractor's outgoing port to be consumed by take.

r = Ractor.new {Ractor.yield 'Hello from ractor'} puts r.take # Prints: "Hello from ractor"

The 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 move argument is the same as for send.

# File ractor.rb, line 626 def self.yield(obj, move: false)   __builtin_cexpr! %q{     ractor_yield(ec, rb_ec_ractor_ptr(ec), obj, move)   } end

Public Instance Methods

Alias for: send
[](sym) click to toggle source

get a value from ractor-local storage

# File ractor.rb, line 823 def [](sym)   Primitive.ractor_local_value(sym) end
[]=(sym, val) click to toggle source

set a value in ractor-local storage

# File ractor.rb, line 828 def []=(sym, val)   Primitive.ractor_local_value_set(sym, val) end
close_incoming → true | false click to toggle source

Closes the incoming port and returns its previous state. 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 ractor.rb, line 733 def close_incoming   __builtin_cexpr! %q{     ractor_close_incoming(ec, RACTOR_PTR(self));   } end
close_outgoing → true | false click to toggle source

Closes the outgoing port and returns its previous state. 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 ractor.rb, line 752 def close_outgoing   __builtin_cexpr! %q{     ractor_close_outgoing(ec, RACTOR_PTR(self));   } end
inspect() click to toggle source 
# File ractor.rb, line 699 def inspect   loc  = __builtin_cexpr! %q{ RACTOR_PTR(self)->loc }   name = __builtin_cexpr! %q{ RACTOR_PTR(self)->name }   id   = __builtin_cexpr! %q{ INT2FIX(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
name() click to toggle source

The name set in Ractor.new, or nil.

# File ractor.rb, line 712 def name   __builtin_cexpr! %q{RACTOR_PTR(self)->name} end
recv()
Alias for: receive
send(msg, move: false) → self click to toggle source

Send a message to a Ractor's incoming queue to be consumed 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

Attempt to send to 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 would be raised immediately, not when ractor will try to receive

If the obj is unshareable, by default it would be copied into ractor by deep cloning. If the move: true is passed, object is moved into ractor and becomes inaccessible to 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 in 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 was 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 ractor.rb, line 582 def send(obj, move: false)   __builtin_cexpr! %q{     ractor_send(ec, RACTOR_PTR(self), obj, move)   } end
Also aliased as: <<
take → msg click to toggle source

Take a message from ractor's outgoing port, which was put there by Ractor.yield or at ractor's finalization.

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 put to outgoing port means that take can be used as some analog of Thread#join (“just wait till ractor finishes”), but don't forget it will raise if somebody had already consumed everything ractor have produced.

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 on 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 closing of the ractor will break the loops 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 ractor.rb, line 693 def take   __builtin_cexpr! %q{     ractor_take(ec, RACTOR_PTR(self))   } end
to_s()
Alias for: inspect

Private Instance Methods

receive() click to toggle source

same as Ractor.receive

# File ractor.rb, line 426         def receive   __builtin_cexpr! %q{     ractor_receive(ec, rb_ec_ractor_ptr(ec))   } end
Also aliased as: recv
receive_if(&b) click to toggle source 
# File ractor.rb, line 497         def receive_if &b   Primitive.ractor_receive_if b end