Add Linux IO::Event::Futex support

.github/workflows/test-futex.yaml

@@ -0,0 +1,33 @@
+name: Test Futex
+
+on: [push, pull_request]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-26.04
+
+    steps:
+    - uses: actions/checkout@v7
+
+    - name: Install liburing with futex support
+      run: sudo apt-get update && sudo apt-get install -y liburing-dev
+
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ruby
+        bundler-cache: true
+
+    - name: Run futex tests
+      timeout-minutes: 5
+      env:
+        RUBYLIB: lib:ext
+      run: |
+        cd ext
+        bundle exec ruby extconf.rb
+        make
+        cd ..
+        bundle exec ruby -e 'require "io/event"; abort "IO::Event::Futex.wait_any is unavailable!" unless defined?(IO::Event::Futex) && IO::Event::Futex.respond_to?(:wait_any); selector = IO::Event::Selector::URing.new(Fiber.current); abort "futex_waitv is unavailable!" unless selector.respond_to?(:futex_waitv)'
+        bundle exec sus test/io/event/futex.rb

ext/extconf.rb

@@ -31,9 +31,16 @@
 
 have_func("rb_ext_ractor_safe")
 have_func("&rb_fiber_transfer")
+have_io_buffer = have_header("ruby/io/buffer.h")
+
+if RUBY_PLATFORM.include?("linux") && have_io_buffer && have_header("linux/futex.h") && have_header("sys/syscall.h")
+	$srcs << "io/event/futex.c"
+end
 
 if have_library("uring") and have_header("liburing.h")
 	have_func("io_uring_prep_waitid", "liburing.h")
+	have_func("io_uring_prep_futex_wait", "liburing.h")
+	have_func("io_uring_prep_futex_waitv", "liburing.h")
 	$srcs << "io/event/selector/uring.c"
 end
 
@@ -57,8 +64,6 @@
 have_func("&rb_fiber_raise")
 have_func("epoll_pwait2(0, 0, 0, 0, 0)", "sys/epoll.h") if enable_config("epoll_pwait2", true)
 
-have_header("ruby/io/buffer.h")
-
 # Feature detection for blocking operation support
 if have_func("rb_fiber_scheduler_blocking_operation_extract")
 	# Feature detection for pthread support (needed for WorkerPool)

ext/io/event/event.c

@@ -3,6 +3,7 @@
 
 #include "event.h"
 #include "fiber.h"
+#include "futex.h"
 #include "selector/selector.h"
 
 void Init_IO_Event(void)
@@ -15,6 +16,10 @@ void Init_IO_Event(void)
 
 	Init_IO_Event_Fiber(IO_Event);
 
+	#ifdef IO_EVENT_FUTEX
+	Init_IO_Event_Futex(IO_Event);
+	#endif
+
 	#ifdef HAVE_IO_EVENT_WORKER_POOL
 	Init_IO_Event_WorkerPool(IO_Event);
 	#endif