Experimental support for async-safe.

Author: samuel-williams-shopify

config/sus.rb

@@ -5,3 +5,6 @@
 
 require "covered/sus"
 include Covered::Sus
+
+require "async/safe"
+Async::Safe.enable!

examples/async-safe/test.rb

@@ -0,0 +1,24 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require_relative "../../lib/io/stream"
+
+require "async"
+require "async/safe"
+
+# Enable concurrent access detection:
+Async::Safe.enable!
+
+# Create a simple stream with some data:
+input, output = IO.pipe
+stream = IO::Stream::Buffered.new(input)
+output.write("Hello")
+
+Async do |task|
+	task.async(transient: true) do
+		data = stream.read(10)
+	end
+	
+	# This should raise ViolationError:
+	stream.read(10)
+end

gems.rb

@@ -31,4 +31,6 @@
 
 	gem "sus-fixtures-async"
 	gem "sus-fixtures-openssl"
+	
+	gem "async-safe"
 end

lib/io/stream/generic.rb

@@ -18,6 +18,14 @@ class Generic
 		include Readable
 		include Writable
 
+		# Check if a method is async-safe.
+		#
+		# @parameter method [Symbol] The method name to check.
+		# @returns [Symbol | Boolean] The concurrency guard for the given method.
+		def self.async_safe?(method)
+			Readable.async_safe?(method) || Writable.async_safe?(method)
+		end
+		
 		# Initialize a new generic stream.
 		# @parameter options [Hash] Options passed to included modules.
 		def initialize(**options)

lib/io/stream/readable.rb

@@ -25,6 +25,31 @@ module IO::Stream
 	#
 	# You must implement the `sysread` method to read data from the underlying IO.
 	module Readable
+		ASYNC_SAFE = {
+			read: :readable,
+			read_partial: :readable,
+			read_exactly: :readable,
+			read_until: :readable,
+			peek: :readable,
+			gets: :readable,
+			getc: :readable,
+			getbyte: :readable,
+			readline: :readable,
+			readlines: :readable,
+			readable?: :readable,
+			fill_read_buffer: :readable,
+			eof?: :readable,
+			finished?: :readable,
+		}.freeze
+		
+		# Check if a method is async-safe.
+		#
+		# @parameter method [Symbol] The method name to check.
+		# @returns [Symbol | Boolean] The concurrency guard for the given method.
+		def self.async_safe?(method)
+			ASYNC_SAFE.fetch(method, false)
+		end
+		
 		# Initialize readable stream functionality.
 		# @parameter minimum_read_size [Integer] The minimum size for read operations.
 		# @parameter maximum_read_size [Integer] The maximum size for read operations.

lib/io/stream/writable.rb

@@ -13,6 +13,20 @@ module IO::Stream
 	#
 	# You must implement the `syswrite` method to write data to the underlying IO.
 	module Writable
+		ASYNC_SAFE = {
+			write: true,
+			puts: true,
+			flush: true,
+		}.freeze
+		
+		# Check if a method is async-safe.
+		#
+		# @parameter method [Symbol] The method name to check.
+		# @returns [Symbol | Boolean] The concurrency guard for the given method.
+		def self.async_safe?(method)
+			ASYNC_SAFE.fetch(method, false)
+		end
+		
 		# Initialize writable stream functionality.
 		# @parameter minimum_write_size [Integer] The minimum buffer size before flushing.
 		def initialize(minimum_write_size: MINIMUM_WRITE_SIZE, **, &block)