Ensure JRuby ivar volatility

Author: pitr-ch

ext/com/concurrent_ruby/ext/SynchronizationLibrary.java

@@ -17,6 +17,7 @@
 import org.jruby.RubyBoolean;
 import org.jruby.RubyNil;
 import org.jruby.runtime.ThreadContext;
+import org.jruby.util.unsafe.UnsafeHolder;
 
 public class SynchronizationLibrary implements Library {
 
@@ -44,6 +45,8 @@ public IRubyObject allocate(Ruby runtime, RubyClass klazz) {
     @JRubyClass(name = "JavaObject", parent = "AbstractObject")
     public static class JavaObject extends RubyObject {
 
+        private volatile int anVolatileField = 0; // TODO unused on JAVA8
+
         public JavaObject(Ruby runtime, RubyClass metaClass) {
             super(runtime, metaClass);
         }
@@ -108,7 +111,31 @@ public IRubyObject nsBroadcast(ThreadContext context) {
 
         @JRubyMethod(name = "ensure_ivar_visibility!", visibility = Visibility.PROTECTED)
         public IRubyObject ensureIvarVisibilityBang(ThreadContext context) {
+            if (UnsafeHolder.SUPPORTS_FENCES)
+                UnsafeHolder.storeFence();
+            else
+                anVolatileField = 1;
             return context.nil;
         }
+
+        @JRubyMethod(name = "instance_variable_get_volatile", visibility = Visibility.PROTECTED)
+        public IRubyObject instanceVariableGetVolatile(ThreadContext context, IRubyObject name) {
+            int tmp;
+            if (UnsafeHolder.SUPPORTS_FENCES)
+                UnsafeHolder.loadFence();
+            else
+                tmp = anVolatileField;
+            return instance_variable_get(context, name);
+        }
+
+        @JRubyMethod(name = "instance_variable_set_volatile", visibility = Visibility.PROTECTED)
+        public IRubyObject InstanceVariableSetVolatile(ThreadContext context, IRubyObject name, IRubyObject value) {
+            IRubyObject result = instance_variable_set(name, value);
+            if (UnsafeHolder.SUPPORTS_FENCES)
+                UnsafeHolder.storeFence();
+            else
+                anVolatileField = 1;
+            return result;
+        }
     }
 }

lib/concurrent/synchronization.rb

@@ -1,6 +1,6 @@
 require 'concurrent/utility/engine'
 require 'concurrent/synchronization/abstract_object'
-require 'concurrent/native_extensions' # JavaObject
+require 'concurrent/synchronization/java_object'
 require 'concurrent/synchronization/mutex_object'
 require 'concurrent/synchronization/monitor_object'
 require 'concurrent/synchronization/rbx_object'

lib/concurrent/synchronization/java_object.rb

@@ -0,0 +1,37 @@
+require 'concurrent/native_extensions' # load native part first
+
+module Concurrent
+  module Synchronization
+
+    if Concurrent.on_jruby?
+      require 'jruby'
+
+      unless org.jruby.util.unsafe.UnsafeHolder::SUPPORTS_FENCES
+        raise 'java7 is not supported at the moment, please use java8'
+      end
+
+      class JavaObject < AbstractObject
+
+        def self.attr_volatile(*names)
+          names.each do |name|
+
+            ivar = :"@volatile_#{name}"
+
+            class_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def #{name}
+                instance_variable_get_volatile(:#{ivar})
+              end
+
+              def #{name}=(value)
+                instance_variable_set_volatile(:#{ivar}, value)
+              end
+            RUBY
+
+          end
+          names.map { |n| [n, :"#{n}="] }.flatten
+        end
+
+      end
+    end
+  end
+end