Add Linux IO::Event::Futex support

.github/workflows/test.yaml

@@ -8,15 +8,15 @@ permissions:
 jobs:
   test:
     name: ${{matrix.ruby}} on ${{matrix.os}}
-    runs-on: ${{matrix.os}}-latest
+    runs-on: ${{matrix.os}}
     continue-on-error: ${{matrix.experimental}}
 
     strategy:
       matrix:
         os:
-          - ubuntu
-          - macos
-          - windows
+          - ubuntu-latest
+          - macos-latest
+          - windows-latest
 
         ruby:
           - "3.3"
@@ -26,13 +26,15 @@ jobs:
         experimental: [false]
 
         include:
-          - os: ubuntu
+          - os: ubuntu-latest
             ruby: truffleruby
             experimental: true
-          - os: ubuntu
+          - os: ubuntu-latest
             ruby: jruby
             experimental: true
-          - os: ubuntu
+          # Use newer packaged liburing for Futex coverage on Ruby head.
+          # Switch back to ubuntu-latest after its 26.04 rollout (2026-11-19).
+          - os: ubuntu-26.04
             ruby: head
             experimental: true
 
@@ -44,8 +46,8 @@ jobs:
         bundler-cache: true
 
     - name: Install packages (Ubuntu)
-      if: matrix.os == 'ubuntu'
-      run: sudo apt-get install -y liburing-dev
+      if: startsWith(matrix.os, 'ubuntu-')
+      run: sudo apt-get update && sudo apt-get install -y liburing-dev
 
     - name: Run tests
       timeout-minutes: 10

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