Add io_select hook.

lib/async/scheduler.rb

@@ -414,6 +414,16 @@ def process_wait(pid, flags)
 			return @selector.process_wait(Fiber.current, pid, flags)
 		end
 
+		# Wait for the specified IOs to become ready for the specified events.
+		#
+		# @public Since *Async v2.25*.
+		# @asynchronous May be non-blocking.
+		def io_select(...)
+			Thread.new do
+				::IO.select(...)
+			end.value
+		end
+
 		# Run one iteration of the event loop.
 		#
 		# When terminating the event loop, we already know we are finished. So we don't need to check the task tree. This is a logical requirement because `run_once` ignores transient tasks. For example, a single top level transient task is not enough to keep the reactor running, but during termination we must still process it in order to terminate child tasks.

releases.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Added support for `io_select` hook in the fiber scheduler, allowing non-blocking `IO.select` operations. This enables better integration with code that uses `IO.select` for multiplexing IO operations.
+
 ### Use `IO::Event::WorkerPool` for Blocking Operations
 
 The `Async::WorkerPool` implementation has been removed in favor of using `IO::Event::WorkerPool` directly. This change simplifies the codebase by delegating worker pool functionality to the `io-event` gem, which provides a more efficient and well-tested implementation.

test/io.rb

@@ -217,4 +217,43 @@
 			read_thread.value
 		end
 	end
+
+	describe ".select" do
+		it "can select readable IO" do
+			expect(Fiber.scheduler).to receive(:io_select)
+
+			input, output = IO.pipe
+
+			begin
+				# Write some data to make it readable
+				output.write("Hello World")
+
+				readables, writables, errorables = IO.select([input], nil, nil, 0.1)
+
+				expect(readables).to have_value(be == input)
+				expect(writables).to be(:empty?)
+				expect(errorables).to be(:empty?)
+			ensure
+				input.close
+				output.close
+			end
+		end
+
+		it "can select writable IO" do
+			expect(Fiber.scheduler).to receive(:io_select)
+
+			input, output = IO.pipe
+
+			begin
+				readables, writables, errorables = IO.select(nil, [output], nil, 0.1)
+
+				expect(readables).to be(:empty?)
+				expect(writables).to have_value(be == output)
+				expect(errorables).to be(:empty?)
+			ensure
+				input.close
+				output.close
+			end
+		end
+	end
 end