[ruby-core:101361] [Ruby master Feature#17378] Ractor#receive with filtering like other actor langauge

Issue #17378 has been updated by matz (Yukihiro Matsumoto).


The `receive` method with a block suggest the block takes an incoming message as a block parameter. So I agree with the proposal if the name is `receive_if`.

Matz.
 

----------------------------------------
Feature #17378: Ractor#receive with filtering like other actor langauge
https://bugs.ruby-lang.org/issues/17378#change-89068

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
----------------------------------------
With discussion with @marcandre, we found good extension for `Ractor.receive` with block.

```ruby
Ractor.receive do |msg|
  if msg is match to condition?
    true
  else
    false
  end
end
```

This block iterates incoming queue's values and the value is passed in `msg`.
If the passed value is matched you want to process, the block should return true and the value will be removed from the queue.
Otherwise (returning falsy value), the value remains in the queue, and other `Ractor.receive` accesses it again.
If there is not more values in queue, the interpreter sleeps until new values are received.

```ruby
r = Ractor.new do |;r|
  loop do
    r, msg = Ractor.receive
    r << msg
    r << 1
    r << 2
    r << 3
  end
end

r.send([Ractor.current, :ping])

# incoming queue: [:ping, 1, 2, 3] (3 is at the last)

Ractor.receive #=> :ping # without a block

# incoming queue: [1, 2, 3]

p Ractor.receive{|msg| msg == 2}
#=> 2 

# incoming queue: [1, 3]
begin
  # exception in the block doesn't touch the queue
  p Ractor.receive{|msg| raise "err"}
rescue => e
  p e.message #=> "err"
end

# incoming queue: [1, 3]
p Ractor.receive #=> 1

# incoming queue: [3]
p Ractor.receive #=> 3
```

With multiple server, we can make it:

```ruby
morning_server = Ractor.new do
  loop do
    task = Proc.new{|obj| "Good morning #{obj}"}
    r, req = Ractor.receive
    res = task.(req)
    r.send([Ractor.current, res])
  end
end

evening_server = Ractor.new do
  loop do
    task = Proc.new{|obj| "Good evening #{obj}"}
    r, req = Ractor.receive
    res = task.(req)
    r.send([Ractor.current, res])
  end
end

morning_server << [Ractor.current, 'ko1']
morning_server << [Ractor.current, 'ko2']
morning_server << [Ractor.current, 'ko3']

evening_server << [Ractor.current, 'ko1']
evening_server << [Ractor.current, 'ko2']
evening_server << [Ractor.current, 'ko3']

def receive r
  Ractor.receive{|(from, msg)|
    r == from
  }[1]
end

p receive(morning_server) #=> "Good morning ko1"
p receive(evening_server) #=> "Good evening ko1"
p receive(morning_server) #=> "Good morning ko2"
p receive(evening_server) #=> "Good evening ko2"
p receive(morning_server) #=> "Good morning ko3"
p receive(evening_server) #=> "Good evening ko3"
```




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