From 73d363c11a63e4b87a0510a378641a9edd99b05f Mon Sep 17 00:00:00 2001
From: Charles Lowell <cowboyd@thefrontside.net>
Date: Thu, 3 May 2012 02:00:04 -0700
Subject: [PATCH] use a lock-free queue to finalize v8 handles.

---
 ext/v8/gc.cc | 43 ++++++++++++++++++++++++++++++-------------
 ext/v8/rr.h  | 30 ++++++++++++++++++++++--------
 2 files changed, 52 insertions(+), 21 deletions(-)

diff --git a/ext/v8/gc.cc b/ext/v8/gc.cc
index 0a97820..1616544 100644
--- a/ext/v8/gc.cc
+++ b/ext/v8/gc.cc
@@ -1,25 +1,42 @@
 #include "rr.h"
 
 namespace rr {
-  VALUE queue;
+  GC::Queue* queue;
 
-  namespace gc {
-    VALUE dequeue(VALUE q) {
-      return rb_funcall(q, rb_intern("pop"), 1, Qtrue);
+  GC::Queue::Queue() : first(0), divider(0), last(0){
+    first = new GC::Queue::Node(NULL);
+    divider = first;
+    last = first;
+  }
+
+  void GC::Queue::Enqueue(void* reference) {
+    last->next = new Node(reference);
+    last = last->next;
+    while (first != divider) {
+      Node* tmp = first;
+      first = first->next;
+      delete tmp;
     }
   }
-  void GC::Push(VALUE phantom) {
-    rb_funcall(queue, rb_intern("<<"), 1, phantom);
+
+  void* GC::Queue::Dequeue() {
+    void* result = NULL;
+    if (divider != last) {
+      result = divider->next->value;
+      divider = divider->next;
+    }
+    return result;
   }
-  void GC::Pop(v8::GCType type, v8::GCCallbackFlags flags) {
-    VALUE next = rb_protect(&gc::dequeue, queue, NULL);
-    rb_set_errinfo(Qnil);
-    if (!NIL_P(next)) {
-      Phantom(next).destroy();
+
+  void GC::Finalize(void* phantom) {
+    queue->Enqueue(phantom);
+  }
+  void GC::Drain(v8::GCType type, v8::GCCallbackFlags flags) {
+    for(Phantom phantom = queue->Dequeue(); phantom.NotNull(); phantom = queue->Dequeue()) {
+      phantom.destroy();
     }
   }
   void GC::Init() {
-    rb_gc_register_address(&queue);
-    queue = rb_eval_string("require 'thread'; Queue.new");
+    queue = new GC::Queue();
   }
 }
\ No newline at end of file
diff --git a/ext/v8/rr.h b/ext/v8/rr.h
index 1b15181..7656f6b 100644
--- a/ext/v8/rr.h
+++ b/ext/v8/rr.h
@@ -20,8 +20,23 @@ protected:
 
 class GC {
 public:
-  static void Push(VALUE phantom);
-  static void Pop(v8::GCType type, v8::GCCallbackFlags flags);
+  class Queue {
+  public:
+    Queue();
+    void Enqueue(void* phantom);
+    void* Dequeue();
+    private:
+      struct Node {
+        Node(void* val ) : value(val), next(NULL) { }
+        void* value;
+        Node* next;
+      };
+      Node* first;      // for producer only
+      Node* divider;
+      Node* last;
+  };
+  static void Finalize(void* phantom);
+  static void Drain(v8::GCType type, v8::GCCallbackFlags flags);
   static void Init();
 };
 
@@ -52,21 +67,17 @@ public:
     Holder(v8::Handle<T> handle, VALUE klass) {
       this->handle = v8::Persistent<T>::New(handle);
       this->value = Data_Wrap_Struct(klass, 0, &Holder::enqueue, this);
-      this->phantom = Data_Wrap_Struct(rb_cObject, 0, 0, this);
-      rb_gc_register_address(&phantom);
     }
     virtual ~Holder() {
       handle.Dispose();
-      rb_gc_unregister_address(&phantom);
     }
   protected:
     VALUE value;
-    VALUE phantom;
     v8::Persistent<T> handle;
 
     static void enqueue(Holder* holder) {
       holder->value = Qnil;
-      GC::Push(holder->phantom);
+      GC::Finalize(holder);
     }
   };
   Ref(Holder* holder) {
@@ -77,7 +88,10 @@ public:
 
 class Phantom : public Ref<void> {
 public:
-  inline Phantom(VALUE value) : Ref<void>(value) {}
+  inline Phantom(void* reference) : Ref<void>((Ref<void>::Holder*)reference) {}
+  inline bool NotNull() {
+    return this->holder != NULL;
+  }
   inline void destroy() {
     delete holder;
   }