Introduce `Fiber::Scheduler#io_select` hook for non-blocking `IO.select`. (#6559)

2 files changed, 29 insertions, 0 deletions

diff --git a/test/fiber/scheduler.rb b/test/fiber/scheduler.rb
index 322564fe6d..3fd41ef6f1 100644
--- a/test/fiber/scheduler.rb
+++ b/test/fiber/scheduler.rb
@@ -197,6 +197,13 @@ class Scheduler
     @writable.delete(io)
   end
 
+  def io_select(...)
+    # Emulate the operation using a non-blocking thread:
+    Thread.new do
+      IO.select(...)
+    end.value
+  end
+
   # Used for Kernel#sleep and Thread::Mutex#sleep
   def kernel_sleep(duration = nil)
     # $stderr.puts [__method__, duration, Fiber.current].inspect
diff --git a/test/fiber/test_io.rb b/test/fiber/test_io.rb
index 4252641cde..821a169e44 100644
--- a/test/fiber/test_io.rb
+++ b/test/fiber/test_io.rb
@@ -172,4 +172,26 @@ class TestFiberIO < Test::Unit::TestCase
     assert_predicate(i, :closed?)
     assert_predicate(o, :closed?)
   end
+
+  def test_io_select
+    omit "UNIXSocket is not defined!" unless defined?(UNIXSocket)
+
+    UNIXSocket.pair do |r, w|
+      result = nil
+
+      thread = Thread.new do
+        scheduler = Scheduler.new
+        Fiber.set_scheduler scheduler
+
+        Fiber.schedule do
+          w.write("Hello World")
+          result = IO.select([r], [w])
+        end
+      end
+
+      thread.join
+
+      assert_equal [[r], [w], []], result
+    end
+  end
 end