src: add multi-context support

This commit makes it possible to use multiple V8 execution contexts
within a single event loop.  Put another way, handle and request wrap
objects now "remember" the context they belong to and switch back to
that context when the time comes to call into JS land.

This could have been done in a quick and hacky way by calling
v8::Object::GetCreationContext() on the wrap object right before
making a callback but that leaves a fairly wide margin for bugs.

Instead, we make the context explicit through a new Environment class
that encapsulates everything (or almost everything) that belongs to
the context.  Variables that used to be a static or a global are now
members of the aforementioned class.  An additional benefit is that
this approach should make it relatively straightforward to add full
isolate support in due course.

There is no JavaScript API yet but that will be added in the near
future.

This work was graciously sponsored by GitHub, Inc.

1 files changed, 11 insertions, 3 deletions

diff --git a/src/handle_wrap.h b/src/handle_wrap.h
index b5918f5dfe..73a43c3a3f 100644
--- a/src/handle_wrap.h
+++ b/src/handle_wrap.h
@@ -22,6 +22,7 @@
 #ifndef SRC_HANDLE_WRAP_H_
 #define SRC_HANDLE_WRAP_H_
 
+#include "env.h"
 #include "node.h"
 #include "queue.h"
 #include "uv.h"
@@ -58,11 +59,17 @@ class HandleWrap {
   inline uv_handle_t* GetHandle() { return handle__; }
 
  protected:
-  explicit HandleWrap(v8::Handle<v8::Object> object, uv_handle_t* handle);
+  HandleWrap(Environment* env,
+             v8::Handle<v8::Object> object,
+             uv_handle_t* handle);
   virtual ~HandleWrap();
 
+  inline Environment* env() const {
+    return env_;
+  }
+
   inline v8::Local<v8::Object> object() {
-    return PersistentToLocal(node_isolate, persistent());
+    return PersistentToLocal(env()->isolate(), persistent());
   }
 
   inline v8::Persistent<v8::Object>& persistent() {
@@ -74,10 +81,11 @@ class HandleWrap {
   static void OnClose(uv_handle_t* handle);
   v8::Persistent<v8::Object> object_;
   QUEUE handle_wrap_queue_;
+  Environment* const env_;
+  unsigned int flags_;
   // Using double underscore due to handle_ member in tcp_wrap. Probably
   // tcp_wrap should rename it's member to 'handle'.
   uv_handle_t* handle__;
-  unsigned int flags_;
 
   static const unsigned int kUnref = 1;
   static const unsigned int kCloseCallback = 2;