[ruby-core:125027] [Ruby Feature#21869] Add receive_all Method to Ractor API for Message Batching

16 Mar 2026

      Issue #21869 has been updated by ko1 (Koichi Sasada).

synacker (Mikhail Milovidov) wrote in #note-4:
...
Yes, it blocks if the queue empty. The method ```receive_all``` accepts a limit parameter:
1. ```limit > 0```: collects up to ```limit``` messages (may return fewer if fewer are queued). Blocks if the queue is empty.
2. ```limit == 0```: returns an empty array immediately (no blocking)
3. ```limit < 0``` or ```nil``` (default): returns all messages from the queue or blocks if the queue is empty
The parameter `limit` is not in the description. Let me clarify `limit == 0`. In above quote, it returns empty array.
If it returns `[]` always, I think we don't need to introduce it.
If it returns existing messages, we can consider about it.

For this purpose, it is possible to introduce another parameter such as `timeout: 0`.

- `receive_all(3, timeout: 0)` returns up to 3 messages already arrived. If there is no messages arrived, returns `nil` (timeout).
- `receive_all(timeout: 1)` returns all messages in a queue, or wait for 1 second. If a message arrived, return the `[received_one_message]`. If no message arrived in 1 second, return `nil`.
- `receive_all(0 or negative parameter)` raises an exception.

We can extend `timeout:` on `receive` method with same manner.

----------------------------------------
Feature #21869: Add receive_all Method to Ractor API for Message Batching
https://bugs.ruby-lang.org/issues/21869#change-116724

* Author: synacker (Mikhail Milovidov)
* Status: Open
* Assignee: ractor
----------------------------------------
**Summary**
The Ractor API provides an excellent mechanism for inter‑thread communication, but it currently lacks a built‑in message batching technique. I propose adding a receive_all method to enable batch processing of messages, which can significantly improve performance in high‑load scenarios.

**Motivation**
In distributed queued systems, processing messages one‑by‑one (as with the current receive method) can introduce unnecessary overhead. Batch processing allows:

Reduced context‑switching overhead.

More efficient I/O operations (e.g., fewer file writes).

Better throughput in high‑concurrency environments.

**Proposed Solution** 
Add a receive_all method to the Ractor API that:

Returns all available messages in the Ractor’s mailbox at once (as an array).

**Demonstration Code** 
Below is a benchmark comparing individual receive vs. batch receive_all:

``` ruby
require 'benchmark'
class RactorsTest

  def initialize(count)
    @count = count
    @ractor1 = Ractor.new(count, 'output1.txt') do |count, filename|
      File.open(filename, 'w') do |file|
        while count.positive?
          message = receive
          file.write("Ractor 1 received message: #{message}\n")
          file.flush
          count -= 1
        end
      end
    end

    @ractor2 = Ractor.new(count, 'output2.txt') do |count, filename|
      File.open(filename, 'w') do |file|
        while count.positive?
          messages = receive_all
          messages.each do |message|
            file.write("Ractor 2 received message: #{message}\n")
          end
          count -= messages.length
          file.flush
        end
      end
    end
  end

  def run1
    @count.times do |i|
      @ractor1.send("Message #{i + 1}")
    end
    @ractor1.join
  end

  def run2
    @count.times do |i|
      @ractor2.send("Message #{i + 1}")
    end
    @ractor2.join
  end
end

records = 1_000_000

test = RactorsTest.new(records)

p [:once, Benchmark.realtime { test.run1 }.round(2)]
p [:all, Benchmark.realtime { test.run2 }.round(2)]
```

**Benchmark Results** 
On my system, receive_all shows ~4x improvement over individual receive:

**Key Observations:**
Ractor1 (using receive): Processes each message individually, resulting in frequent I/O calls.

Ractor2 (using receive_all): Processes all queued messages at once, minimizing I/O overhead

-- 
https://bugs.ruby-lang.org/